WO1992006636A1 - Three-dimensional tomographic system - Google Patents

Abstract

An industrial CT system is provided for three-dimensional imaging which includes a three-dimensional cone beam of hard radiation fixed with respect to a two-dimensional scintillation detector array (29). The object (25) is positioned on a turntable (24) interposed between the radiation source (12) and detector array (29). Data from two-dimensional views are stored as the object is rotated on the turntable (24) about a fixed axis. The data is sufficient upon completion of one revolution to construct a transparent three-dimensional image of the object. A positioning encoding arrangement (50) adjusts for variations in the object's mass density to optimize scan-compute times while enhancing image resolution.

Description

THREE-DIMENSIONAL TOMOGRAPHIC SYSTEM

This invention relates generally to computerized tomographic systems and more particularly to such systems designed specifically for industrial applications.

The invention is particularly applicable to three di- mensional transparent images produced by computed tomographic inspection systems for industrial applications and will be described with particular reference thereto. However, it will be appreciated by those skilled in the art that the invention can also be used to develop two dimen- εional images through any cross-sectional plane of the irra¬ diated object as well as three dimensional exterior dimen¬ sioning.

INCORPORATION BY REFERENCE The following material is incorporated herein by refer- ence: a) An article entitled "Practical Cone-Beam Algorithm" by L.A. Feldkamp et al, reprinted from Journal of the Opti¬ cal Society of America A, Vol. 1, page 612, June 1984 issue; b) An article entitled "High-Speed, Three Dimensional X-Ray Computed Tomography: The Dynamic Spatial

Reconstructor" by Robb et al, published in PROCEEDINGS OF THE IEEE, Vol. 71, No. 3, March, 1983; c) U.S. Patent 3,758,723 to Green et al dated Septem¬ ber 11, 1973; d) U.S. Patent 3,881,110 to Hounsfield et al dated April 29, 1975; e) U.S. Patent A,288,695 to Walters et al dated Sep¬ tember 8, 1981. f) U.S. Patent 4,298,800 to Goldman dated November 3, 1981; g) U.S. Patent 4,466,112 to Covic et al dated August 14, 1984; n) U.S. Patent 4,506,327 to Tom dated March 19, 1985. BACKGROUND OF THE INVENTION

A. THE MEDICAL FIELD

Generally speaking, computerized tomography is a modern technique initially developed for use in the medical field to provide a non-invasive means for revealing internal or¬ gans and tissues of the human body in cross-section to aid in medical diagnosis, surgery, etc. Essentially, an X-ray beam (also including, in certain instances gamma radiation) is passed through the body and the attenuation difference between the transmitted beam and the detected beam is sensed by a detector system, digitized and stored in a computer. The beam is then rotated in one plane to a different angular position and the attenuated beam's energy at that position similarly recorded. The process continues for 360°, at which time the computer images the data recorded to develop a two dimensional picture of a cross-sectional slice taken through the patient which corresponds to the plane in which the X-ray beam was rotated. The X-ray beam is then trans¬ versely moved and the process repeated to develop another picture of a cross-sectional slice of the patient. By tak¬ ing a plurality of such transversely spaced slices and stacking them one on top of the other, a three dimensional transparent view can be constructed by the computer.

The first commercial application of computerized axial tomography (CAT) is attributed to Hounεfield in 1972 and used a pencil beam with a single detector. The beam and detector were simultaneously rotated and then linearly translated to develop an appropriate scan of the organ. This is conventionally referred to as the first generation scanner. To reduce the time required for the scan, the pen¬ cil beam ray was replaced by a beam of X-rays orientated in a thin fan-shaped ^"pattern with the attenuated rays in the fan sensed by a plurality of detectors on the opposite side of the body. Various detector arrays and detector-beam movements were subsequently developed in second, third and fourth generation scanners, all of which were directed to increasing the speed of the scan. In all scanners of the first through fourth generation, a three dimensional view of the scanned object was obtained by first computing an image of a cross-sectional slice and then stacking such slices to construct a three dimensional transparent or translucent image.

There are inherent problems in medical scanners of the first through fourth generation which preclude their use in industrial applications. Conceptually, any system that ro¬ tates a beam to obtain several one dimension images which are subsequently combined to produce a cross-sectional "slice" and which then translates the beam to build a plu¬ rality of slices requires a scan-compute time which is sim- ply too slow for industrial inspection purposes. Also, any fan beam in reality has a finite width or a depth while the cross-sectional slice is assumed to be a planar line. Ac¬ cordingly, there are numerous prior art patents relating to detectors, collimators, scatter shields, etc., which have been designed to reduce the beam width and improve image resolution. Finally, in three dimensional imaging, the com¬ puter uses various formulae, assumptions and corrections to calculate what the irradiated object looks like in the space between the slices. Where high resolution and accuracy is required, numerous slices must be taken to build an accurate three dimensional image.

In addition to such problems, first through fourth gen¬ eration scanners cannot accurately image certain moving or¬ gans such as the heart. Accordingly, there have been recent developments in the medical field reported in the Robb et al article which utilize a cone beam instead of a fan beam and an area detector in place of the one dimensional detector arrays to provide such a system.

It is known that a cone beam of X-rays can be developed and that such beam can be projected onto a fluoroscopic screen or recorded on photographic film for two dimensional imaging. A number of papers have presented formulae for cone beam back projections which are used to construct the images in a computed tomographic system. Despite the number 5 of papers, the use of cone beams in three dimensional X-ray computed tomographic systems has only been reported as suc¬ cessfully practiced in the medical scanner(s) described in the Robb et al article. In the Mayo Clinic scanner de¬ scribed in Robb's paper, multiple X-ray tubes are placed 0 around a 160° arc of a circular gantry which mechanically rotates about the patient while carrying a diametrically opposed fluorescent screen. The screen records two dimen¬ sional shadow data for each of the X-ray cone beam sources which are described as being fourteen in number. The orien-

-- tation of the object to be scanned is such that the distance from the source of radiation to the object is significantly greater than the distance from the object to the detector so that the transmitted beams in the cone striking the screen can be viewed as parallel beams to permit reconstruction in

20 the manner of a fan beam slice system. Conceptually, the system developed at the Mayo Clinic is sound and represents a significant advance in the medical field permitting heart studies and the like. The geometries of the system are such that while adjacent cone beams can be formed to uniformly

25 irradiate an object, the attenuated beams in the adjacent or fringe areas will interfere with one another before striking the detector. For this reason, the fluorescent screen is positioned close to the patient. While the interference can be compensated for at the detectors, commercial objects hav-

30 ing high mass densities would produce weak fringe signals making it difficult to obtain accurate high resolution sig¬ nals or increasing the scan time, etc.

In the related nuclear medicine field, Technicare pat¬ ent 4,302,675 discloses an adjustable collimator in co bina-

-- tion with a scintillation camera where the pinhole axes in the collimator are movable to record various incident angles of gamma rays emitted from an object to construct a simulat¬ ed three dimensional image of the object. Also, U.S. Patent 4,322,684 to Hounsfield discloses a three dimensional i ag- ing technique utilizing nuclear magnetic resonance where resonance is induced in a plurality of planar slices through an object which is rotated about a first axis and then fur¬ ther rotated about a second axis. The slices are then inte¬ grated to obtain a three dimensional view. Neither nuclear medicine application uses X-rays emitted from a point source travelling in straight lines. B. INDUSTRIAL APPLICATIONS

While it can be appreciated that numerous principles of computer tomography are applicable to both medical and in- dustrial aprlications, there are several requirements for tomographic systems which are unique to industrial systems. Cost considerations require a scanning time which is signif¬ icantly shorter than what is acceptable in the medical field. In addition, there are many assembly line applica- tions which require three dimensional inspections of fast moving objects. Also, in many instances, industrial appli¬ cations must produce accurate images capable of detecting very small dimensional inconsistencies. In this sense, in¬ dustrial tomographic applications based on scan time-image resolution considerations are more severe than medical ap¬ plications. Finally, in many applications, the size of the specimen presents inherent beam penetration problems which cannot be necessarily solved by changing from soft to hard x-rays or increasing the energy ir*-ensity of the source, etc.

Industrial radiography (the recording of the differen¬ tial absorption of hard radiation such as X-rays, gamma rays, etc. on photographic film to disclose two dimensional images) has long been used to detect internal physical im- perfections such as voids, cracks, flaws, segregation, porosities, and inclusions in the finished article of manu¬ facture. Additionally, the use of a fluorescent screen to permit high speed visualization of the X-ray shadow images has also been long utilized. In U.S. Patent 3,758,723 to Green et al a fluorescent screen is utilized in combination with an optic lens, a light intensifier and a vidicon tube (electron beam camera) to record a picture which is snatched and projected onto a television monitor while the article being viewed is indexed to another position for its next two dimensional X-ray picture. In other industrial applications such as discussed in U.S. Patent 4,392,237 to Houston, Xenon detectors have conventionally been used with collimated pen¬ cil X-ray beams which act as flying spot scanners for bag¬ gage systems, bottling plants and the like. The Houston patent expands the pencil beam concept to a fan beam princi¬ pal in combination with a plurality of detectors (not en¬ tirely dissimilar to the second generation systems described above) to detect two dimensional views of objects passing through the fan beam. Despite many statements in the liter- ature to the contrary, industrial inspection techniques which have been successfully commercialized prior to our invention essentially use one dimensional beams projected onto one or two dimensional detectors to record two dimen¬ sional pictures of the inspected object. Within the literature, an article entitled "Practical Cone-Beam Algorithm" published in the Journal of the Optical Society of America, (one of the articles incorporated by reference herein) by L.A...Feldkamp et al, reported op a lab¬ oratory system consisting of a microfocus x-ray soutce, a single axis rotational stage and the x-ray image intensifier with associated electronics. The paper demonstrated a con¬ volutionback projection algorithm for use in CT image con¬ struction using a cone beam. The system discussed in the Feldkamp paper inherently possesses several advantages over conventional CT systems. Principally, the system is conceptually able to compute a three dimensional image upon a single 360° revolution of the irradiated object about one of its axis. Additionally, the problem associated with the "thickness" of the beam in fan cone systems is eliminated by this system. Thus, image resolution is enhanced while the scan-compute time is significantly lessened. The system disclosed in the Feldkamp article has been used in closely controlled laboratory conditions on small parts and is fun¬ damentally sound. However, a number of problems are encoun- tered when the system, in its fundamental concept, is ap¬ plied to various CT industrial applications where part geom¬ etry, size or environment require system modifications to either permit imaging or improve image resolution and/or speed. SUMMARY OF THE INVENTION

Accordingly, it is a principal object of the present invention to provide an improved, industrial computerized tomographic system which can produce sharp images of indus¬ trial objects and the like in a short time. This object along with other features of the invention is achieved in a computerized tomographic industrial radia¬ tion system capable of constructing a three dimensional transparent image of at least a portion of an industrial part or similar object which includes i) a point source gen- erator for generating a non-pulsed, three dimensional cone beam of hard radiation, ii) a collimator associated with the generator for controlling the cone angle and the peripheral configuration of the cone beam, iii) a positioning mechanism for locating the object in the path of the cone beam such that a predetermined volumetric portion of the object is exposed to the three dimensional cone beam of hard radia¬ tion, and iv) a two dimensional detector arrangement fixedly aligned with the point source generator and located on the side of the object opposite the object's side exposed to the hard radiation. The detector arrangement is of the type which receives attenuated radiation and converts the radia¬ tion through scintillation into a two dimensional shadow image and includes digitizing means for collecting the two dimensional shadow image into an ordered array of digitized numbers such that each digitized number in the array corre¬ sponds to the energy level of attenuated beams of radiation at a given location in the array. A computerized arrange¬ ment is provided for storing the digitized numbers and imag¬ ing two as well as three dimensional transparent image of a predetermined volumetric portion of the irradiated object. The positioning mechanism includes means for positioning the object in a three dimensional relationship relative to the source and means for intermittently rotating the object rel¬ ative to the point source and the detector arrangement about only one axis of the object through a predetermined angular movement. Importantly, the single axis of rotation is cen¬ tered about the predetermined volumetric portion of the ob¬ ject to be imaged and not necessarily about the object's geometric center to permit high image resolution of a de- fined portion of the object through no more than one revolu¬ tion of the object.

In accordance with a more specific feature of the in¬ vention, the time for completing the scan is reduced while the image resolution is enhanced by rotating the irradiated object off center from its geometric center such that the distance from the object's center of rotation to the detec¬ tor screen is a minimum when the mass volume of the object penetrated by the hard radiation is at a maximum. This nor¬ malizes the range of radiation sensed by the detector ar- range ent during rotation to permit image enhancement while also minimizing the time required to digitally sense the shadow image developed in the scintillation screen.

In accordance with still yet another more specific as¬ pect of the invention, the rotation of the irradiated object is along an elliptical or alternatively an eccentric, arcuate path as contrasted to a circular path such that the greatest volumetric mass portion or density of the object penetrated by the radiation is positioned closest to the detector arrangement to minimize adverse magnification ef- fects on the scintillation screen at the outermost bounda¬ ries of the radiation cone beam.

In accordance with another aspect of the invention when the object's size is such that the object has at least two cross-sectional areas in any two orthogonal planes which is greater than the area of the detector* arrangement, the posi¬ tioning mechanism positions the object so that the cone beam initially passes through a first portion of the peripheral surface of the object and the rotating means is effective to rotate the workpiece about a first axis which is offset from the center of the object through one revolution. Thereaf¬ ter, the positioning means translates the object such that the cone beam passes through a second portion of the periph¬ eral surface whereat the rotating means is effective to ro¬ tate the object through only one revolution about a second axis. The imaging means is effective to construct a three dimensional image of the entire object. Preferably, the first and second axis of rotation are coordinated relative to the mass volume density of the object to position the largest mass volume closest to the detector system to mini- mize scan time and enhance image resolution. Further, it is possible to obtain a three dimensional image of the object by not sampling the object through a predetermined angle of rotation and positioning the maximum mass density of the irradiated object to pass through the predetermined angle to reduce the scan-compute time.

In accordance with another aspect of the invention, the positioning means initially locates the object at a position between the generator source and the detector mechanism such that the initial shadow image produced by the detector mech- anism represents substantially the complete cross-section of the object in a two dimensional spatial relationship. The imaging means is effective to construct a two dimensional cross-sectional image, i.e. a digitized radiograph, corre¬ sponding to the shadow image and the operator is provided with a mechanism for manually selecting a portion of the cross-sectional image for volumetric viewing. The position¬ ing means is responsive to the actuation of the operator mechanism to move the object closer to the generator source and thus increase the magnification and enhance the image resolution of the detector arrangement. The imaging means constructs a volume image encompassing only the selected portion of the cross-sectional area when the object is ro¬ tated through one complete revolution to permit greater res¬ olution of small object details. In accordance with a more specific feature of the in¬ vention, the system optimizes the maximum object size for a given scintillation screen which can be three dimensionally imaged, per se, as well as in combination with the pan and zoom feature discussed above. Definitionally, the system is orientated along x, y and z axes perpendicular to one anoth¬ er with orthogonal planes passing through any two of the three axes. The scintillation device is situated in a plane passing through the y-z axis and the x axis intersects the y-z plane at a center point. The generator's point source is situated on the x axis and extends a distance to the cen¬ ter of rotation of the object equal to a distance SRAD and the center of the scintillation screen extends a distance in the opposite direction from the object's center of rotation equal to a distance DRAD. The object has a maximum y diε- tance extending along the y axis and a maximum z distance extending along the z axis. The positioning means is opera¬ ble in combination with the collimator associated with the point source to position the object along the x axis between the point source and the scintillation screen such that the object's maximum y distance when divided by SRAD does not exceed the scintillation screen's y dimension when divided by DRAD added to SRAD and the object's maximum z distance when divided by SRAD does not exceed the scintillation screen's z dimension when divided by DRAD added to SRAD so that the entire object can be three dimensionally imaged upon only one complete rotation of the object.

In accordance with still yet another specific feature of the invention, the resolution capability of the system disclosed is optimized when the zoom feature of the inven¬ tion is employed to establish an image which is clear enough to distinguish voxels of "R" size based upon the finite di¬ ameter of the point source, "FSS" (focal spot size) , and the actual finite size of individual detectors, "DS" (detector size) , assuming a satisfactory detector matrix size and a sufficient number of two dimensional slices. The main pro¬ cessor, utilizing the encoder information from the system drives, initially calculates, by means of similar triangle ratios, the distance SRAD assuming a point source at the detector screen and a focal spot of diameter FSS and then calculates the distance SRAD assuming a point source at the generator and a diametrical detector size of DS and chooses the longest SRAD distance. Should the voxel size then es¬ tablished be too large for the industrial application, the optimally spacing between the point source and detector screen along the x-x axis may be varied by iterative calcu¬ lations of the processor until the desired resolution is obtained or the system's dimensional limits are met.

In accordance with another specific feature of the in¬ vention, the scan-compute time and image resolution capabil- ity is increased by utilizing a priori information to dynam¬ ically vary the flux or intensity of the hard radiation emitted from the source and/or dynamically vary the integra¬ tion of the flux or attenuated radiation recorded by the detector array. The a priori information is established by an initial scan of the object which correlates the drive encoders to the various mass densities of the object taken at each angular increment while the object is rotated about its y-y axis. The intensity of the generator is then varied during the object's rotation to produce a more homogeneous light photon range between two dimensional slices throughout the scan to permit more sensitive detector readings over an overall shorter scan time. The digitized detector readings are subsequently modified to account for the variation in radiation intensity. Alternatively, the detectors are con- ventional current integrated devices, and in accordance with known noise signal considerations must integrate light pho¬ tons emitted from the scintillation screen correlated to large object mass densities over a longer period of time than that for small mass densities. The a priori informa- tion is utilized to vary the integration time in a fashion somewhat similar to that used in the dynamic flux variations of the generator beam.

In accordance with a still more specific object of the invention, the irradiated object need not be stopped in its rotational motion while two dimensional image data is being taken and the number of images taken can be varied in number to permit three dimensional inspection of at least selected volumetric portions of industrial objects moving at fast linear speeds indicative of an assembly line environment. It is thus an object of the invention to provide an industrial CT system which permits a three dimensional transparent image of a large object to be taken in a short time.

It is another object of the invention to provide an industrial CT system which permits sharp resolution of three dimensional images of irregularly shaped objects.

It is another object of the invention to provide an industrial CT system which permits sharp resolution of large, irregularly shaped objects in a short time. It is still yet another object of the invention to pro¬ vide an industrial CT system which not only can take three dimensional transparent views of the object but also two dimensional views through any plane of the object. It is still yet another object of the invention to pro¬ vide an industrial CT system which provides an operator con¬ trolled zoom feature permitting three dimensional viewing of a selected volumetric portion of an irradiated object.

In accordance with the immediately preceding object, it is still a further object of the invention to provide a CT system which can image small voxels of the irradiated ob¬ ject.

Yet another object of the invention is to provide an industrial CT system which is quicker in scan time than that of the prior art.

Still a further object of the invention is to provide an industrial CT system which produces higher image resolu¬ tions than that previously afforded in such systems.

Still another object of the invention resides in an improved industrial CT system resulting from the combination of some or all of the features enumerated above.

Still a further object of the invention is to provide a simple and economical CT system and/or a functionally im¬ proved CT system. These and other objects of the invention will become apparent to those skilled in the art upon reading and under¬ standing the detailed description of the preferred embodi¬ ments of the invention set forth below.

BRIEF DESCRIPTION OF THE DRAWINGS The invention may take physical form in certain parts and arrangement of parts, preferred embodiments of which will be described in detail and illustrated in the accompa¬ nying drawings which form a part hereof and wherein:

FIGURE 1 is a schematic plan view of a scan enclosure; FIGURE 2 is a schematic side elevation view of the scan enclosure of FIGURE 1;

FIGURES 3, 4 and 5 illustrate pictorially the steps in a three dimensional reconstruction process employed in the invention;

FIGURE 6 schematically illustrates the various control functions associated with the scan enclosure;

FIGURE 7 is a schematic pictorial representation of the hardware associated with the system. FIGURES 8a, 8b and 8c schematically illustrate plan views of the rotation of an object within the scan enclo¬ sure;

FIGURES 9a and 9b illustrate various paths of irradiat¬ ed object rotation within the scan enclosure; FIGURES 10a, 10b and 10c illustrate schematically the positioning of an object within the scan enclosure;

FIGURE 11 illustrates schematically the zoom feature of the system;

FIGURE 12 illustrates schematically a portion of the system collecting X-ray data and includes FIGURES 12a, 12b and 12c; and

FIGURE 13 schematically illustrates a specific indus¬ trial application of the system and includes FIGURES 13a and 13b. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings wherein the showings are for the purpose of illustrating preferred embodiments of the invention only and not for the purpose of limiting the same, there is shown in Figures 1 and 2 a scan enclosure 10 which is completely lined with lead to prevent radiation leakage therefrom. Within scan enclosure 10 is an x-ray generator source 12. X-ray generator 12 is conventional and generates from a point source a cone shaped beam of hard radiation. A suitable x-ray generator is model number MN 451 produced by Philips GmbH which has a rated power source of 450 kv although, depending on the application and size, generators with a power source as low as 125 kv can be used. While generator 12 is conventionally defined as a point source generator, in practice the x-ray source has a finite focal spot which, for the application discussed in this specifica¬ tion, typically range between 1.5 mm and 4 mm. Other X-ray sources have different ranges. Attached to x-ray generator 12 is a collimator 13 which shapes the peripheral pattern of the cone beam boundary and controls the cone angle of the cone beam. Collimator 13 is conventional and will not be described in further detail and is to be distinguished from cone shaping mechanisms which selectively control the inten¬ sities of x-ray beams emitted from generator 12. X-ray gen¬ erator 12 is generally adjacent one side of scan enclosure 10 while an x-ray detector means 15 is situated generally adjacent the opposite side of scan enclosure 10. Detector means 15 can comprise any one of several arrangements con¬ ventional in the art. In the embodiment disclosed in Fig¬ ures 1 and 2, detector means 15 includes an image intensifi- er tube 16 and a video camera 17. Reference may be had to the vidicon-lens intensifier arrangement designated by nu¬ merals 20-31 in U.S. Patent 3,758,723 to Green et al (incor¬ porated by reference herein) for a description of a suitable intensifier tube 16-video camera 17 arrangement which can be used in the present invention. As is conventionally known, intensifier tube 16 converts the attenuated beam's x-ray energy to light through scintillation and a two dimensional fluorescent screen or crystal is used to develop a "shadow image" of the irradiated part. Video camera 17 is coupled to image intensifier tube 16 by optics, either lens or fi¬ ber, and scans the shadow image raster and converts the light energy to analog data. Optionally, a scatter rejec¬ tion grid 18 can be inserted ahead of the scintillation screen in intensifier tube 16. Scatter rejection grid 18 is a two dimensional array of slits and/or pinholes, each of which is focused on the focal spot of x-ray generator 12 to permit only x-rays that are transmitted along a straight line from x-ray generator 12 to be transmitted to detector means 15. X-ray generator 12 and detector means 15 are fixed to one another by means of a yoke or gantry 20. Gantry 20 is provided with an appropriate, conventional drive mechanism to permit simultaneous movement of x-ray generator 12 and detector means 15 in the y and z directions. For reference purposes, the x-x, y-y and z-z axis will have that orienta¬ tion shown in Figures 1 and 2 and planar surfaces passing through any two different axes are, by definition, orthogo¬ nal to one another. With the axes definition thus estab¬ lished, it is to be noted that the focal spot of x-ray gen- erator 12 lies on the x-x axis which intersects the center of intensifier tube 16. Optionally, the distance along the x-x axis between x-ray generator 12 and detector means 15 can be varied by an x-drive mechanism not shown, and if used in the system this is the only relative movement permitted between x-ray generator 12 and detector means 15. (This could be accomplished by constructing gantry 20 as two L shaped members slotted in the x-x direction.) A door 22 is provided to gain access to the interior of scan enclosure 10 for loading and unloading objects to be inspected. A turn- table 24 is positioned between x-ray generator 12 and detec¬ tor means 15. A drive, not shown, is provided for rotating turntable 24. Also, a drive, not shown, is provided for moving turntable 24 in the x-x direction. It should be ap¬ preciated that because the system is concerned with relative positioning, drives could be provided for turntable 24 to move in the y-y and z-z direction and, if so provided, gantry 20 would not be required to effect movement of gener¬ ator 12 and detector means 15 in the y-y and z-z direction. An encoder, not shown, is provided for each of the drive mechanisms. Referring now to Figure 7, an object 25 to be irradiat¬ ed is placed on turntable 24 and collimator 13 is adjusted so that the radiation's cone beam angle "A" is just suffi¬ cient to project over the outer peripheral surfaces of ob- ject 25 in the y-y and z-z direction. After the transmit¬ ting beams of radiation impact object 25, the attenuated beams of radiation strike what is defined herein as the two dimensional scintillation screen 27. "Scintillation screen" 27 as used herein including the claims hereof means either a fluoroscopic screen or a two dimensional flat scintillation crystal. A suitable scintillation crystal would be cesium iodide doped with thallium and a suitable fluoroscopic screen may, for example, consist of gadolinium oxysulfide or zinc cadmiumsulfide. As well known in the art, scintil- lation screen 27 simply converts the energy of the attenuat¬ ed x-ray beams striking screen 27 into light photons having a correlatable energy, (i.e. wavelength, color) and when all the transmitted beams of radiation striking scintillation screen 27 are viewed, a two dimensional shadow image 28 is observed.

Light photons from scintillation screen 27 are detected by a detector arrangement 29. As discussed with reference to the embodiment shown in Figures 1 and 2, detector ar¬ rangement 29 could comprise a vidicon camera or a like cam- era such as shown in U.S. Patent 3,758,723 to Green et al with or without a fiber optic light intensifier and with or without a lens focusing and/or magnification system inter¬ posed between scintillation screen 27 and detector arrange¬ ment 29. As the shadow image raster is scanned by the vidicon camera an analog output is serially recorded and subsequently digitized. In this manner, a digital radio¬ graph (a cross-sectional view of object 25 as orientated in Figure 7 corresponding to the shadow image) can be recon¬ structed. Detector arrangement 29 could alternatively com- prise an array of multi-channel individual detectors. Various photosensitive devices suitable for use in such an array are noted in U.S. Patent 3,881,110 to Hounsfield et al, incorporated by reference herein. Alternatively, an area CCD device (charge coupled device) such as those identified by Motorola catalog number listed in U.S. Patent 4,298,800 to Goldman (incorporated by reference) can be uti¬ lized. Conceptually, each individual detector is located at a precise position in an ordered array or matrix shown ex¬ tending in a y-z plane and each detector generates an analog signal (usually current) indicative of the energy of the light photons striking the detector which in turn is corre¬ lated to the energy of the attenuated x-ray beam's energy at that particular point. The analog signals are serially col¬ lected and digitized at which time each signal represents a pixel. Typically the arrays have 512 by 512 individual channel detectors and in some instances 1024 by 1280 detec¬ tors for sharp image viewing.

Referring now to Figures 3, 4, 5 and 7, preferably ob¬ ject 25 is rotated about a central axis 26 for a predeter- mined angle, stopped and detector means 15 actuated to record detector 29 readings. During this scan, the detec¬ tors record sufficient data so that a two dimensional, digi¬ tized radiograph of the cross-section of the object or field-of-view can be constructed. Object 25 is then rotated through another predetermined angle and a second field-of- view recorded and the process is usually continued until the object has rotated through a complete revolution of 360°. Typically 720 field-of-views are recorded in one revolution in about 120 seconds. This is a very rapid rate and, in contrast to medical applications, generator 12 is not pulsed during the scan even though cone shaping mechanisms may be employed to vary the intensity of beams or beam portions within the cone. Thus, each detector in effect records a "pencil" beam of attenuated radiation and this has occurred 720 times by the time the rotation is completed. Each detector thus records x, y, z data correlated to each angu¬ lar position of object 25 and all of the data is stored. Thus, each detector has recorded in one rotation information equal to that recorded in one complete rotation of a first generation medical scanner and that data for that detector can be used to generate one crosε-sectional slice of object 25. Similarly, one row of detectors (y or z axis) is equiv¬ alent to the fan beam detector arrangement of the second through fourth generation medical scanners. Thus, the sys- tern gathers information in one revolution equivalent to that obtained by y (or z) revolutions of second through fourth generation medical scanners. The data for each detector can then be utilized to construct computerized two dimensional slices (typically 512 or 256 slices) of object 25 shown as cross-sectional planes cutting through the object as shown in Figure 4 or voxels as shown in Figure 5 similar to that which is now directly recorded with fan beam CT scanners and this data can then be utilized to construct three dimension¬ al, transparent images using conventional, computer solved, algorithms. In addition, two dimensional images can be con¬ structed through any inclined or oblique plane passing through object 25. There are, however, some fundamental differences in the data obtained by the detectors in the present system when compared to that of the fan beam sys- terns. For example, only the radiation beams falling on the x-x axis correspond to the prior art fan beam arrangements. The other rays are inclined and reference may be had to L.A. Feldkamp' ε article (incorporated by reference herein) for an appropriate convoluted back projection algorithm which ac- counts for such inclination and which can be used in the system of the present invention. Another difference is that imaging of off-center voxels result in a magnification of the voxel detected by scintillation screen 27. While it is easy to mathematically account for the magnification, there are difficulties associated therewith in an industrial set¬ ting which the system of the present invention overcomes.

Referring now to Figure 6, the imaging system of the present invention includes three separate systems indicated by dash lines in the drawing. The systems include a data acquisition system 40, an imaging processor system 41 and an operator console 42. Each system 40, 41, 42 is intercon¬ nected with one another.

Data acquisition system 40 includes, as described with reference to scan enclosure 10 of Figures 1 and 2, x-ray tube 12, x-ray detector syεtem 15 and in the εenεe that scan encloεure 10 iε relevant to the drive positioning object 25 between x-ray tube 12 and x-ray detector system 15 a scan table designated as numeral 16 in Figure 6. In this sense, scan table 16 includeε an R drive 45 for accurately rotating object 25 through timed angular incrementε, a Y drive 46 and a Z drive 47 accurately poεitioning x-ray tube 12 and x-ray detector εystem 15 in the y-y and z-z direction, and an X drive 48 for accurately poεitioning object 25 in the x-x direction between x-ray tube 12 and x-ray detector means 15. Optionally, X drive 48 could also include a drive for vary¬ ing the spacing between detector means 15 and x-ray source 12. Each of the drive mechanisms 45-48 includes convention¬ al drive motors, drive mechanics, drive electronics and an encoder associated with its respective drive position to indicate the exact position of the εystem component con¬ trolled by the drive. Also, each drive has an interface to a scan table digital controller 50. Scan table digital con¬ troller not only controls drives 45-48 but also synchronizes x-ray controls during the scan proceεε. Commands are sent to and from the scan table controller 50 from image proces¬ sor 41 and operator console 42 to initiate the scan process as well as to indicate the particular scan protocol. As noted, scan enclosure digital controller 50 controls the intensity of the beams emitted from x-ray tube 12 through x-ray power supply 52 and also included in the power supply control 52 is the arrangement for varying the intensity of the x-ray beams within the cone beam should the optional dynamic flux variation concept be utilized. Scan table dig- ital controller 50 also controls the x-ray data acquisition and control electronics ("XDAC") 54. XDAC 54 samples the data from detector system 15 as well as controlling when to sample the data as synchronized by the scan enclosure con¬ troller 50. Sample data from XDAC 54 is then sent to image processor 41 for reconstruction. XDAC 54 includes a data digitizer which converts analog data from x-ray detector εyεtem into digital data and stores the data into a high speed digital memory, i.e. a buffer. The data digitizer iε interfaced to image processor 41. XDAC 54 also includes a data digitizer controller which takes inputs from scan table digital controller 50 and instructs the data digitizer, usu¬ ally as a function of position of object 25, when to take its sample.

Image proceεεor 41 receives the data from data acquiεi- tion syεtem 40 and processes the data into the desired three dimensional density volume as well as processing other imag¬ es and performing data analysiε functions. The major hard¬ ware sectionε of image processor 41 include a main computer or main processor 60 which preferably is a Micro Vax II con- figured with the proper peripherals to control all functions of the CT system. Main processor 60 is coupled to several major subsystems within image procesεor 41 aε well as to the data acquisition syεtem and the operator console 42. The subsystems in image procesεor 41 include a disk controller and disk drives 61 which are used for program software and data storage. A mag tape controller and mag tape drive 62 is used to transfer softwar and data to and from the CT system. An imager 63 is use to dis], _~y processed images on a monitor in the operator's console <*>2. Imager 63 has its own dedicated memory, look up tables and digital video processor to perform imaging processing functions and image manipulation functions. Functions which the imager can per¬ form are window and center functions, pan and zoom func¬ tions, image manipulation functions, image metric functions, image processing functions, alpha numeric generation, cursor generation, high speed load functions, graphic functions and color presentations. Systems which are used to refine col¬ lected data sent to imager 63 include a mass memory 65 which storeε data collected from data acquiεition εystem 40 te po- rarily while scanning of the object 25 iε in progreεε. Al¬ so, mass memory 65 is used to allow rapid access to raw data and image data for reconstruction of the images and array proceεεors 66 are provided to proceεε the large amount of data from data acquisition system 40 into images. Rapid floating point operations can be performed by array proces¬ sors 66 which are interfaced to mass memory 65 as well as main processor 60. Back projection hardware 67 is used to perform the back projection for x-ray reconstruction and iε connected to both array processorε 66 and mass memory 65 to allow rapid reconstruction of the image. A suitable algo¬ rithm utilized in the back projector 67 to construct three dimensional images is set forth in the Feldkamp article cit¬ ed above. Finally, a data acquisition εystem interface 68 allows rapid transfer of data collected from data acquisi- tion system 40 to image procesεor 41. Also, data acquiεi¬ tion system interface 68 transferε bi-directionally the con¬ trol of status commands between data acquiεition εystem 40 and image procesεor 41.

Hardware for operator console 42 includes an operator terminal and keyboard 70 connected to image processor 41, image viewing monitor 71 connected to imager 63 and an oper¬ ator scan control and display control panel 72 connected to terminal 70 and monitor 71 and also to scan table controller 50 and x-ray power supply 52. Operator terminal and key- board 70 preferably includes a Micro Vax II GPX 19 inch work station monitor, keyboard and mouse integrated into the con¬ sole structure and preferably is menu driven by the mouse. The menus contain the particular scan protocol and each pro¬ tocol contains all the necessary a priori information needed to operate the system automatically. During operation, ter¬ minal 70 will display critical scan data information on mon¬ itor 71 which will have window, centering and cursor display functions for use with the reconstructed object picture. Control panel 72 provides for direct operator control for certain specific functions such as start scan control, abort scan control, emergency stop, x-ray enable, x-ray diεable, hold scan, resume scan, window and center knobs, track ball for cursor and plain selectors, knobs for size, shape, image intensity, etc. The general εyεt :m has been explained with reference to variouε components and the components, per se, are conven¬ tional. The manner in which the components are combined and operated, however, render the syεtem particularly suitable for industrial CT applications. Reference may be had to Figures 10 and 11 for discussion of what may be described as a pan and zoom feature of the invention. Generally speak¬ ing, for a fixed "x" dimension between the focal spot of x-ray generator 12 and scintillation screen 27 of detector means 15, collimator 13 is constructed to form a right angle cone of x-ray beams having a cone angle A such that the cone beam will strike the entire area of scintillation εcreen 27. If scintillation screen 27 is rectangular in area, then collimator 13 wilx form the cone beam as a rectangular beam which will expand to encompass the y-z area of scintillation εcreen 27. Object 25 iε then placed on turntable 24 and the turntable's X drive actuated to poεition object 25 within the cone beam at a distance from the focal source generator 12 such that a two dimensional digitized radiograph of the entire object 25 can be viewed in monitor 71. The operator can now, by means of a control such as a track ball 75 on control panel 72, select a εpecific volume of object 25 which can be viewed in three dimenεional detail. The opera¬ tor positions the area to be volume scanned between two cur¬ sor lines 77, 78 and pulls down and actuates the appropriate menu on terminal 70. When this is done, the Y and Z drives are actuated to focus the selected volumetric portion of ob¬ ject 25 to be imaged which will be centered with respect to generator 12 and scintillation screen 27 while the X drive on turntable 24 is actuated to move object 25 closer to gen- erator 12 such that the portion desired to be scanned sub¬ stantially encompasses the y-z area of scintillation εcreen 27. In this manner, the three dimensional image can be en¬ hanced to detect very fine discontinuitieε, porosities, de¬ fects, incluεionε, etc. in the critical maεε portionε of the object to be scanned.

The actual image resolution of the CT εyεtem iε a func¬ tion of the focal εpot size of the generator ("FSS" in Fig¬ ure 10) , the detector resolution (i.e. the diametrical size of the detectors in the channeled array, "DS" in Figure 10), the detector sampling (i.e. the number of slices), the dis¬ tance from the focal spot source to the center of rotation of the object (def ned as "SRAD" in Figure 10) , the distance from the detector to the center of rotation of the object (defined as "DRAD" in Figure 10) and the final image matrix size (pixel array) .

In practice, the actual focal εpot size, FSS, is known and the size of an individual detector DS in detector means 15 is also known and the size of the matrix of the screen iε alεo known. The distances SRAD and DRAD are not known. Accordingly, Figures 10a through 10c illustrate the various system relationshipε utilized to eεtabliεh a zoom poεition neceεεary to resolve a 22 um contrast object. First, as shown in Figure 10a, the limiting resolution due to the ac¬ tual focal εpot εize, FSS, is determined by constructing a triangle with its apex at the detector and its base at the focal spot, FSS, and the same size aε the focal spot. This assumes that there is an infinitesimally small detector with a finite focal spot in the detector plane. Next, at a dis¬ tance DRAD from the infinitesimal detector a second base line, i.e. the resolution, is drawn through the triangle. By similar triangles, the ratio of the focal spot base line to the DRAD base line (resolution size) is the εa e as the ratio of SRAD plus DRAD is to DRAD. The formula then for the resolution baεed on the focal spot size ^« (FSS * DRAD)/(SRAD + DRAD). In Figure 10a, assuming the actual focal spot of generator 12 is 25 urn , then for a resolution of 22 urn , the SRAD and DRAD distances are shown to be 38 mm and 305 mm respectively.

Next, the limiting resolution due to the detector size is considered as shown in Figure 10(b) . Thiε iε done by constructing a triangle with its apex at the point focal spot FS of the generator and its base at the detector in the detector plane and equal to the same size as an individual detector. This assumes that there is an infinitesimally small focal spot on the generator with a finite sized detec¬ tor. At a distance SRAD from the infinitesimal focal spot, FS, another base line is drawn through the triangle. By similar triangles, the ratio of the detector base line, DS, to the SRAD base line, i.e. the resolution, is the same aε the ratio of SRAD plus DRAD is to SRAD. The formula for the limiting resolution due to the point detector size - (DS * SRAD)/(SRAD + DRAD). In the example given for this calcula¬ tion in Figure 10b, if the size of the individual detector is approximately 1.98 mm in diameter, a detector resolution size of 22 urn will occur at a DRAD distance of 305 mm and an SRAD distance of 38 mm. The fact that the dimensionε for DRAD and SRAD are equal for Figures 10a and 10b is a coinci¬ dence. In practice, the relation will be limited by either Figure 10a or 10b and the calculation establishing the long- est SRAD will be uεed. Figure 10c is basically the same figure as shown in Figure 11 and shows that for a detector arrangement 29 hav¬ ing a matrix size which computes out to an area encompassing a circle having an approximate diameter of 9 inches and a cone angle of "A", a sphere or a scan cylinder of approxi¬ mately 1 inch in diameter at the SRAD and DRAD distances given can be viewed in three dimensions with a 22 urn. reso- -lution assuming a sufficient number a sliceε are taken. The 22 ii iε equivalent to the voxel size as graphically demon- strated in Figure 5. Thus, it is a specific feature of the invention that for any given CT system, the main processor 60, for any given voxel size, will instruct scan table con¬ troller 50 to control X drive 48 for turntable 24 as well aε R drive 45 and Y and Z driveε 46, 47 to produce the desired resolution of a volumetric portion of object 25 or alterna¬ tively, for a desired volumetric portion as established by cursor lines 77 and 78 the minimum voxel size of the εystem will be computed. Should it occur that for a desired volu¬ metric viewing portion of object 25, the resolution is not small or sharp enough (or for the desired resolution, the volumetric view is smaller than desired) , it is possible, as noted above, to modify gantry 20 to vary the total x-x spac¬ ing (SRAD plus DRAD) and collimator 13' s cone angle "A" ac¬ cordingly. (The collimator, in its simple form, is simply a circular hole in a block which can be positionally located relative to the x-ray source to vary the cone angle "A") . Main processor 60 can then iteratively calculate the optimal DRAD and SRAD distances established by Figures 10a and 10c to produce the desired resolution and scan cylinder size. Also, in this connection, εince the intenεity of the hard radiation varies as a power function relative to the dis¬ tance travelled by the radiation, the smallest overall path distance of the X-rays is maintained, i.e. SRAD plus DRAD relative to the desired resolution and the volumetric por- tion of the object to be imaged. Referring now to Figures 8a through 8c, whenever the size of object 25 is such that the cross-sectional area of any two orthogonal planes through the object exceeds the cross-sectional area of scintillation screen 27, three di- mensional imaging of the object proceeds in at least two stepε. For example, the object 25 is rotated about two axes 81, 82 in the y-y direction which are offset from the geo¬ metric center 80 of object 25. Specifically, object 25 iε initially rotated through one complete revolution on axis 81 and the appropriate drives actuated to repoεition the object whereupon it iε rotated upon its second offset axis 82 through one complete revolution. Image procesεor 41 con¬ structs a three dimensional object image from the data ob¬ tained in both rotations. As best indicated in Figure 8b, n any multi-step, off center scan procedure, there will be an object position during the rotation where the radiation must, in effect, be transmitted through the object where its thickneεε or maεε volume density is some multiple of the object when compared to that thickneεε or denεity dimension of the object at the start of the initial off center scan. At this "multiple" mass volume density, the x-ray attenuated beams energy is significantly less than the energy level of x-ray beams pasεing through less dense portions of the ob¬ ject during the off center rotation. When this occurs and as is well known in the art, the scattering and absorption effects attributed to the denεity reduce the number of x-ray photons which strike and are absorbed in scintillation screen 27 when compared to that paεεing through less dense portions of the object. Accordingly, the bundle of light photons emitted from screen 27 which are optically coupled to detectors 29 is reduced. This increaεeε the time re¬ quired for the detector to generate an adequate image signal whether the detector be of the counting type or whether the detector be of the current integration type which measures the total energy over a time period long enough to reduce signal noise. This problem becomes more severe for those x-ray beams emanating from the point source which do not impact at the center of scintillation εcreen 27. The beamε at the outer portion of the cone beam array magnify the out- ermoεt voxelε of the object and should the denseεt or "thickeεt" portion of the object be εituated at the outer- moεt portion of the cone beam, the photon energy εenεed by each detector at the outermoεt poεition of the detector ar¬ ray iε further reduced for a voxel than that of a voxel im- aged at the center of scintillation screen 27. The imaging problem becomes further aggravated aε the SRAD diεtance be¬ comes smaller relative to the DRAD diεtance. Also of sig¬ nificant concern iε that the intenεity of the radiation iε a function of the total path distance of the radiation raised to some power and the path diεtance of the detectorε at the outermost portion of the array iε longer than that through the center. Accordingly, the time for the image to develop when the denεest portion of the object is at the edge of the cone beam rays is materially increased or the image enhance- ment is weakened. Several features of the present invention are provided to overcome or minimize such problems as fol¬ lows:

1) It should be noted from viewing Figures 8a-8c that if cross-sectional sliceε were taken at equal angular incre- mentε throughout the 360° rotation at both off center axes 81, 82, there will be an overlap of two dimensional images. Accordingly, it iε unnecessary to record field-of-view imag¬ es during the rotational angle where one of the overlaps occurs for the second and subsequent rotations. Thuε, the time to complete a multiple off-center scan is less than the time it would require to complete full, equal angular field-of-view εcanε through 360° for each center of rota¬ tion. The overall εcan time iε further reduced by position¬ ing the object on the turntable so that the volumetric por- tion of the highest mass density of the object is recorded in only one off-center rotation and the overlap of high vol¬ ume mass densitieε can be skipped in subεequent off-center rotationε. The encoders for the drives can be programmed based on a sample image to establish the optimum axes of rotation 81, 82. Alternatively, fixtures can be developed for turntable 24 based on the geometry of industrial object 25.

2) Referring now to Figures 9a and 9b, normally object 25 is rotated about a central axis extending in the y-y di- rection so that any off center voxel 85 would rotate as shown in Figure 9a about a circular path (and this circular rotation would occur even for the multiple offset axis rota¬ tion εhown in Figure 8). However, for certain especially configured parts, i.e. parts elongated in one direction, and for the reasons noted above (and whether or not imaging oc¬ curs when the part is rotated only through one revolution or the nart has to be translated and rotated through multiple rev. Jtions) , it is desirable to impart motion in the x-x direction to turntable 24 while the object is rotated such that the thickest portion or the greatest mass density por¬ tion of the object is spaced closest to scintillation screen 27 while the object is rotated. Thus, an otherwise off cen¬ ter voxel 86 positioned in the densest part of the object might move in an elliptical path about the axis of rotation such that the ellipεe occurs closest to scintillation screen 27 where the field-of-view image iε taken or recorded and the ninor axis of the ellipse which is furthest from scin¬ tillation screen 27 is, for all intents and purposes, not within the cone beam. A path could be programmed into pro- grammer 60 and regulated by the encoder in X drive 48. By so orientating object 25 relative to the scan geometry, the overall scan time is reduced and the image reεolution en¬ hanced.

3) In conjunction with or without the optimum posi- tioning of object 25 as discussed with references to Figures 8 and 9, it is possible to dynamically vary the flux or the intensity of the hard radiation aε diεcussed in U.S. Patent 4,506,327 which iεεued March 19, 1985, assigned to General Electric Company and incorporated by reference herein. Gen- erally, the intensity of radiation from generator 12 is in¬ creased or decreased to correspond to the various densities of object 25. More particularly and with reference to FIG¬ URE 12, an initial εcan of object 25 is taken and the read¬ ings stored in proceεεing εyεtem 41 and used to develop a priori information. This information iε then uεed by encod¬ er 85 to control the intenεity of radiation emitted from generator 12 and to also instruct data digitizer controller 86 when to read the X-ray data from the detector syεtem. Aε indicated previously, controller 86 may be a scanning con- troller which scanε aε a raεter and controls the readings of detectors in detector arrangement 29, which in FIGURE 12 are, for illustration purposes, shown as individual detec¬ tors D, , D₂, D-_», etc. in a multi-channel array. The analog readings of detector arrangement 29 (current, time) are se- rially digitized in data digitizer 87 and stored in buffer 88 which acts as a high speed memory. Because of the beam intensitieε required for induεtrial applications, the detec¬ tors D are of the current integrating type and not of the type which count photons. In accordance with the general concepts of the G.E. patent, the intensity of the emitted radiation from generator 12 is varied for each field-of-view image depending on the overall denεity of object 25 at that field-of-view. This permits a normalization of the inte¬ grated readings recorded by detectors D so that the εensi- tivity of the detectorε may be optimized (i.e. readings within a narrower band) to improve reεolution. However, in the G.E. patent, multiple εcanε of the object are required which are not necessary in the present invention. More spe¬ cifically, a cone shaping mechanism 89 can be employed to vary the intensity of individual beams of radiation within the cone beam. The dynamically varied radiation beams are correlated by encoder 85 and data digitizer controller 86 to individual detectors D-, , D₂, D3, etc. or to certain areas of the detectors within the multi-channel detector array. Cone shaping mechanisms are generally wedge shaped or other geo¬ metrically configured mechanisms, such as parabaloid (for example see U.S. Patent 4,288,695 incorporated by reference herein) which are positionally located in a variable manner in front of the source of generator 12 to control the inten- εity of radiation beams or portions of beamε of radiation εtriking individual detectorε D or detector portions within detector array 29. The analog εignalε generated for indi¬ vidual detectorε D,, D₂, D-, , etc. is diagrammatically illus¬ trated in the dynamic flux variation schematic of FIGURE 12. The current senεed by each detector D for a conεtant time period T iε integrated and shown as the area under the curve for each detector which iε digitized in data digitizer 87. Since the radiation beams have been varied for object densi¬ ty, the deviation in the signal senεed between individual detectors is significantly narrowed when compared to that which would have been sensed if no corrections were made. This permits each field-of-view image to have a sharp reso¬ lution since the range of light spectrum sensed by the de¬ tectorε iε "normalized" εo that the sensitivity of the de- tectors (i.e. compensation for noise) can be optimized to improve resolution. The digitized data is then adjusted in the procesεing εyεtem 41 by the εtored a priori information to permit accurate image construction.

4) In practice, the densities and geometries of man industrial objects 25 require high power generators operat¬ ing at constant maximum power. Such applications limit the uεe of cone shaping mechanisms other than for purposes of correcting or normalizing the different path lengths of the radiation. The graph entitled Dynamic Flux Integration in FIGURE 12 uses the same concepts discussed with respect to Dynamic Flux Variation to develop a priori information and then uti¬ lizes the information to vary the time detectors D,, D₂, D , etc. senεe the light photons to "normalize" the analog sig¬ nals developed by the detectors. As in the dynamic flux variation concept discusεed in paragraph 3 above, the dynam¬ ic flux integration concept can be utilized either in the εenεe of varying the integration time for all detectors in different field-of-view imageε or varying individual detec¬ tor εignals within the detector array to enhance each field- of-view image. Further, it is possible to combine Dynamic Flux Integration with Dynamic Flux Variation.

In the normal batch type operation of the system as described in the arrangement shown in Figures 1 and 2, the R drive rotates object 25 through a discrete angle and stops and the two dimensional "digitized radiograph" iε taken at that time whereupon the turntable rotateε through another set angle and the digitized radiograph developed at that position. Generally speaking, 720 field-of-view imageε (digitized radiographε) can be taken in only 120 seconds. In the imaging process the 720 field-of-view imageε produce detector readingε which are utilized to conεtruct 512 croεε-εectional εliceε of object 25 εimilar to that generat- ed in the medical CT syεtemε, i.e. usually perpendicular to an object's axis. In the system disclosed, the cross-sec¬ tional sliceε can be reconstructed perpendicular to any plane through the object as well as generating any two di¬ mensional "slice" picture through any plane of the object. The number of crosε-εectional εlices which are reconstructed views performed by the computer utilizing appropriate algo¬ rithms can be varied to a lesεer number, i.e. 256 or 128, with a correεponding reduction in the time (from 120 sec- ondε) to conεtruct the image - that is the time to recon- struct vis-a-vis computer 60 iε the limiting factor and not the time to obtain field-of-view data) and also a corre¬ sponding lock in the resolution of the three dimensional transparent image which is reconstructed. While this is an entirely acceptable method for non-invasively inspecting geometrically complex objects on a batch type basis, there are many industrial applications where particularly critical portions of an object must be inspected for each object mov¬ ing on an assembly line.

One typical application would be the inspection of the neck portion of bottles in a bottle manufacturing facility. In such applications, line speed is typically between 150 and 250 feet per minute with a slight spacing between the bottles. On the other hand, only a portion of the neck of a bottle is critical to the bottle inspection and the neck density of the bottle is relatively low and somewhat con¬ stant. Accordingly, relatively few two dimensional views, typically 36 per revolution, need be taken to develop suffi¬ cient acceptance/rejection parameters. As εhown in Figure 13, this is accomplished by providing a plurality of scin- tillation screens 27 which are aligned with the necks of bottles B, , Bo, B-, moving past the εcreenε in an assembly line fashion and which receive radiation preferably from one x-ray generator source 12. A belt arrangement 94 positioned below scintillation screens 27 engages the body portions of bottles B and is tensioned so that each bottle B,, B₂, etc., is rotated at a constant rate through one complete revolu¬ tion from the point that each bottle enters the scintilla¬ tion screen arrangement at its entry end 95 to the point where each bottle exits the scintillation screen arrangement at its exit end 96. The entire bottling line, at least at the point where the bottles B enter entry end 95 to the re¬ jection point 91 where defective bottles are removed from the bottling line by a reject chute 92, is timed by a strobe light 93 or similar counter so that each bottle B, , B , etc. is individually identified. As shown in Figure 13, strobe 93 is correlated to belt 94 and the line speed to instruct controller 86 to read the detector arrangement 29. As shown in the integration graph of Figure 13, the analog signal is integrated during a very short "on" time because the bottle has a relatively low density at its neck portion. This "on" time TQ is in the range of 2-3 millisecondε compared to an "on" time in the range of 100 milliεeconds or so for fairly dense objects irradiated in scan enclosure 10 on a "batch" process basis. The data iε then digitized in A/D device 87 and stored in buffer 88 during the read data time T, . At the bottle line speedε diεcuεsed, the bottle travels between 10 to 20 thousandths of an inch during T_Q. Thus, the reso¬ lution capability or defect size which the system is able to ascertain (voxel εize) iε limited to 10 to 20 thousandths of an inch and preferably is double the T_Q distance, i.e. 0.020 to 0.040". During the time bottles B^ , B₂, B, , are within scan enclosure 10, multiple scintillation screenε 27 are effective to record one field-of-view εimultaneously for the number of bottles within the path of the cone beam. The composite field-of-view image for multiple bottles B is then simultaneouεly proceεsed by the reconstruction processors 41 to further reduce the image reconstruction time. That is, the 120 second time to procesε 512 εliceε iε reduced by that time to proceεs only 36 sliceε and that time iε further ef- fectively reduced by the number of bottleε simultaneouεly irradiated through multiple detector εcreenε 29. The image recon truetion proceεε occurs during the time the bottles leave exit end 96 and the time they enter reject station 91 and the distance therebetween is determined by the bottle line speed. Becauεe identity of the individual bottles has been maintained, a permanent CT record of each rejected bot¬ tle can be maintained, etc. which will be of significant value to the manufacturing procesε.

The invention has been deεcribed with reference to a preferred embodiment. Obviously alterations and modifications will occur to others upon a reading and under¬ standing of the specification. It is our intention to in¬ clude all such modifications and alterations insofar as they come within the scope of the present invention. It is thus the esεence of the invention to provide an improved industrial CT syεtem based on an area detector re¬ cording digitized radiographs as the object iε rotated only about one axis and in which the image resolution is enhanced while the scan time iε materially decreased by correcting for the geometry of the irradiated object.

Claims

Having thus defined my invention, we claim:

1. A computerized tomographic industrial radiation system for constructing a three dimensional transparent im¬ age of at least a portion of an industrial part or similar object comprising: a point source generator for generating a non-pulsed, three dimensional cone beam of transmitted rays of hard ra¬ diation; collimator means asεociated with εaid generator for controlling the cone angle and the peripheral configuration of said cone beam; poεitioning means for locating said object in the path of said cone beam such that a predetermined volumetric por¬ tion of said object is exposed to said three dimension cone beam of hard radiation; two dimensional detector means fixed with reεpect to εaid point source generator and located on the opposite side of said object for recording the attenuated radiation, said detector means including a scintillation screen receiving attenuated radiation and converting εaid radiation through scintillation into a two dimensional shadow image and digi¬ tizing means for converting εaid two dimenεional shadow im¬ age into a ordered array of digitized numbers, each digi¬ tized number in εaid array corresponding to the energy level of an attenuated beam of radiation at a given location in said array; said positioning means including means for positioning said object in a three dimensional relationship relative to said source and means for intermittently rotating said ob¬ ject relative to said point source and εaid detector means about only one axis of εaid object through predetermined angular incrementε, εaid axiε centered at εaid predetermined volumetric portion and not neceεεarily at said object's geo¬ metric center; means for recording said digitized numbers during the time εaid rotating means is unactuated; and imaging means for constructing a three dimensional transparent image of said predetermined volumetric portion from said digitized number after a predetermined number of angular rotations whereby said three dimensional image can be rapid r constructed.

2. The system of claim 1 wherein said detector means includes a two dimensional detector array developing a plu¬ rality of analog signals, each signal indicative of the en¬ ergy of the light photons emitted from said scintillation screen at discrete locations in said array; and εaid object is positioned by εaid positioning means to rotate along a predetermined path about an axis extending through said object such that the object iε positioned clos¬ est to said scintillation device when εaid cone beam paεεes through the largest mass volume portion of said object.

3. The system of claim 2 wherein said detector means includes a two dimensional detector array developing a plu¬ rality of analog signals, each signal indicative of the en¬ ergy of the light photons emitted from εaid scintillation screen at discrete locations in said array; and said object is positioned by εaid positioning means to rotate in a non-circular path such that the largest mass volume portion of said object is closest to said scintilla¬ tion screen as said object is rotated through one revolution about one of its axis.

4. The system of claim 2 wherein εaid rotating means is effective to rotate said object along a generally ellip¬ tical path between said generator and said detector means, said elliptical path having, by definition, a major axis and a minor axiε, said major axiε correlated to the largeεt diametrical distance through the object and said minor axis correlated to the smalleεt diametrical distance through said object whereby said detector means is not subjected to vari¬ ations in light intensity otherwise possible during its ro- tation to improve image resolution; and means aεsociated with εaid rotation means and said digitizing meanε to cor¬ rect εaid digitized numbers for the diεtance of said gener¬ ally elliptical path.

5. The system of claim 1 wherein said object has at least two cross-sectional areas in any two dimenεional planeε orthogonal to one another each of which iε greater than the area of εaid scintillation screen; εaid poεitioning meanε operative to i) poεition εaid object εo that said cone beam initially paεεeε through a firεt portion of the periph¬ eral surface of εaid object, ii) actuate εaid rotating means to rotate said workpiece about a first axis which is offset from the center of said object through only one revolution, iii) translate said object along at leaεt one of the plane axiε εo that said cone beam passes through a second portion of the peripheral surface of εaid object and iv) actuate εaid rotating means to rotate said object through only one revolution about a second axis and said means for construct- ing effective to conεtruct a three dimensional image of the entire object.

6. The system of claim 5 wherein said detector means includes a two dimensional detector array developing a plu¬ rality of analog signals, each signal indicative of the en¬ ergy of the light photons emitted from said scintillation screen at discrete locations in said array; and εaid object iε poεitioned by εaid poεitioning means to rotate along a predetermined path about an axis extending through said object such that the object iε positioned closest to said scintillation device when said cone beam passes through the largest mass volume portion of said ob¬ ject.

7. The syεtem of claim 6 wherein said detector meanε includeε a two dimenεional detector array developing a plu¬ rality of analog εignals, each signal indicative of the en¬ ergy of the light photons emitted from εaid scintillation screen at discrete locations in said array; and said object iε positioned by εaid positioning meanε to rotate in a non-circular path such that the largest mass volume portion of said object is closest to said scintilla¬ tion screen aε εaid object is rotated through one revolution about one of its axis.

8. The system of claim 1 wherein said positioning means initially locates said object at a position between said generator and said detector means such that said ini¬ tial shadow image produced by εaid detector means represents substantially the complete cross-section of said object in a two dimensional spatial relationship; said imaging means effective to conεtruct a two dimenεional image of εaid ob¬ ject corresponding to said εhadow image; operator means for manually selecting a portion of said crosε-εectional image for volumetric viewing; εaid positioning means reεponεive to actuation of εaid operator means to move said object closer to εaid generator to increase the magnification and enhance the resolution of εaid detector means, and said im¬ aging means effective to construct a volume image of said object encompasεing only εaid selected two dimenεional por¬ tion of said object.

9. The εyεtem of claim 8 wherein εaid system iε orien¬ tated along x, y and z axeε perpendicular to one another with orthogonal planes passing through any two of said axiε; εaid scintillation screen is situated in a plane pass- ing through said y-z axis and having y and z dimensions ex¬ tending along said y axis and said z axis respectively, εaid x axiε intersecting said y-z plane at a center point there¬ of, said generator having a point source situated on εaid x axiε and extending a distance from the center of rotation of said object equal to an SRAD distance, said scintillation εcreen extending a diεtance on the opposite side of εaid object along εaid x axiε from εaid object'ε center of rota¬ tion equal to a DRAD diεtance, εaid object having a y dis¬ tance extending along said y axiε and a z diεtance extending along εaid z axiε; εaid poεitioning meanε operable to poεition εaid object along εaid x axis between εaid point source and εaid scin¬ tillation device εuch that said object's y dimension when divided by said SRAD distance does not exceed εaid scintil- lation device's y dimension when divided by εaid DRAD diε¬ tance added to said SRAD diεtance and εaid object'ε z diε¬ tance when divided by εaid SRAD diεtance doeε not exceed εaid εcintillation device'ε z dimenεion when divided by said DRAD diεtance added to said SRAD diεtance v/hereby the object through a volume portion thereof encompaεεing itε y and z dimenεions can be imaged in three dimensions through only one revolution of said object.

10. The system of claim 8 wherein said εyεtem iε ori¬ entated along x, y and z axeε perpendicular to one another with orthogonal planeε paεεing through any two of εaid axiε; εaid εcintillation εcreen iε situated in a plane pasε- ing through εaid y-z axiε and having y and z dimensions ex¬ tending along said y axiε and εaid z axiε reεpectively, said x axiε interεecting εaid y-z plane at a center point there¬ of, εaid generator having a point εource situated on said x axis and extending a diεtance from the center of rotation of εaid object equal to an SRAD diεtance, εaid scintillation εcreen extending a diεtance on the oppoεite εide of said object along said x axis from said object's center of rota¬ tion equal to a DRAD diεtance, εaid object having a y dis¬ tance extending along said y axis and a z distance extending along said z axis; said generator has a finite, circular source of diamet¬ rical diεtance, FSS, centered on εaid x axiε at a distance from the center of rotation of said object equal to said SRAD diεtance, εaid poεitioning meanε operable to position said object at a distance on εaid x axiε between εaid finite source and said scintillation device such that a voxel hav¬ ing as εmall a dimenεion as R can be imaged in three dimen¬ sions by only one revolution of said object when the ratio of R divided by said DRAD distance is equal to the ratio of εaid FSS diameter divided by εaid DRAD diεtance added to said SRAD distance.

11. The system of claim 8 wherein said system is ori¬ entated along x, y and z axes perpendicular to one another with orthogonal planes passing through any two of said axis; said scintillation screen is εituated in a plane paεs- ing through said y-z axis and having y and z dimensions ex¬ tending along said y axis and said z axis respectively, said x axiε interεecting εaid y-z plane at a center point there¬ of, εaid generator having a point εource situated on εaid x axis and extending a distance from the center of rotation of said object equal to an SRAD distance, εaid scintillation εcreen extending a diεtance on the opposite side of said object along said x axis from said object's center of rota¬ tion equal to a DRAD diεtance, εaid object having a y diε¬ tance extending along said y axis and a z distance extending along said z axis; said detector means further includes a plurality of detectorε optically connected to said εcintillation εcreen, each detector recording light photon energy correεponding to a digitized number in said array, each detector capable of recording light photon energy striking an area correlated to an area on said scintillation screen equal to a minimum diε¬ tance of DS in the y or z direction, εaid positioning means operable to position said object at an SRAD distance εuch that a voxel having aε small a dimension of R can be imag- ined in three dimenεions by only one revolution of εaid ob¬ ject when the ratio of R divided by εaid SRAD diεtance iε equal to the ratio of said DS distance divided by said SRAD distance added to εaid DRAD diεtance.

12. The εyεtem of claim 11 wherein εaid generator haε a finite source of diametrical diεtance, FSS, such the ratio of R divided by εaid DRAD diεtance iε equal to the ratio of said FSS diameter divided by εaid DRAD diεtance added to εaid SRAD distance and said positioning means iε operable to select the largest of the two SRAD distances.

13. The εyεtem of claim 12 wherein εaid poεitioning meanε operable to poεition εaid object along εaid x axis between εaid point source and said scintillation device such that εaid object' ε y dimension when divided by said SRAD distance does not exceed said εcintillation device'ε y di- menεion when divided by εaid DRAD diεtance added to εaid SRAD diεtance and εaid object's z distance when divided by εaid SRAD diεtance doeε not exceed εaid εcintillation de¬ vice' ε z dimenεion when divided by εaid DRAD diεtance added to said SRAD diεtance whereby the object through a volume portion thereof encompaεsing its y and z dimensions can be imaged in three dimensions through only one revolution of said object.

14. The εystem of claim 13 wherein said detector means includes a two dimensional detector array developing a plu¬ rality of analog εignalε, each εignal indicative of the energy of the light photons emitted from said scintillation screen at discrete locations in said array; and said object is positioned by said positioning means to rotate along a predetermined path about an axis extending through said object such that the object is positioned clos¬ est to said scintillation device when said cone beam passes through the largest mass volume portion of said object.

15. The system of claim 14 wherein said rotating means is effective to rotate said object along a generally ellip¬ tical path between said generator and said detector means, said elliptical path having, by definition, a major axis and a minor axis, said major axis correlated to the largeεt dia¬ metrical distance through the object and said minor axis correlated to the smallest diametrical distance through said object whereby said detector means is not subjected to vari¬ ations in light intensity otherwise possible during its ro- tation to improve image resolution; and means associated with said rotation meanε and said digitizing means to cor¬ rect said digitized numbers for the distance of εaid gener¬ ally elliptical path.

16. The system of claim 1 wherein said scintillation screen extends along a y and a z axis perpendicular to one another for generating visible light in response to the en¬ ergy level of attenuated radiation impacting said screen; said point source of said generator centered along an x axis orthogonal to said z and said z axis and situated at a predetermined distance along said x axis from the center of said scintillation screen, said generator operable to pro¬ duce a plurality of transmitted beams of radiation emanating from said point aouxce in generally izrfight lines which define a three d^"inifensional coneshaped array; dynamic flux variation means effective to uniformly vary the intenεity of tranεmitting beams of radiation which εtrike as attenuated beams of radiation εaid scintillation screen in said y and z direction, said intensity of εaid beams correlated to the mass denεity of εaid object along said x axis as said object rotates about a y axis such that the intenεity of the tranεmitting beams pasεing through high mass densities of said object at a specific angular rotation is higher than the beam intensity passing through low mass portions of said object at a different angular rotation whereby the energy levels of the attenuated beams striking said scintillation device are at a lesser variance than that which would occur had the intensity of said transmitting beams been uniform; and said imaging means correlated to said dynamic flux variation means and effective to adjust said digitized num¬ bers in accordance with the variation in intenεity of said transmitting beams of radiation.

17. The system of claim 16 wherein said detector means includes a two dimensional detector array developing a plu¬ rality of analog εignalε, each εignal indicative of the en¬ ergy of the light photonε emitted from εaid εcintillation εcreen at discrete locations in εaid array; and εaid object iε positioned by εaid positioning means to rotate along a predetermined path about an axis extending through εaid object εuch that the object is positioned clos- eεt to said scintillation device when said cone beam passes through the largest maεε volume portion of εaid object.

18. The εyεtem of claim 17 wherein εaid rotating meanε iε effective to rotate εaid object along a generally ellip¬ tical path between εaid generator and εaid detector means, εaid elliptical path having, by definition, a major axiε and a minor axis, εaid major axiε correlated to the largeεt dia¬ metrical distance through the object and εaid minor axis correlated to the smallest diametrical distance through εaid object whereby said detector means is not subjected to vari¬ ations in light intensity otherwise possible during its ro- tation to improve image resolution; and means associated with said rotation means and said digitizing means to cor¬ rect said digitized numbers for the diεtance of εaid gener¬ ally elliptical path.

19. The εyεtem of claim 17 wherein εaid poεitioning meanε initially locateε εaid object at a position between εaid generator and said detector means such that said ini¬ tial shadow image produced by εaid detector meanε represents substantially the complete cross-section of εaid object in a two dimenεional εpatial relationship; said imaging means effective to construct a two dimensional image of εaid ob¬ ject correεponding to said shadow image; operator means for manually selecting a portion of said cross-εectional image for volumetric viewing; said positioning means responεive to actuation of εaid operator means to move said object closer to said generator to increase the magnification and enhance the resolution of said detector means, and εaid im¬ aging means effective to construct a volume image of εaid 5 object encompassing only said selected two dimensional por¬ tion of said object.

20. The syεtem of claim 19 wherein said system is ori¬ entated along x, y and z axes perpendicular to one another with orthogonal planes passing through any two of said axiε; said scintillation εcreen iε situated in a plane pass- - ing through said y-z axiε and having y and z dimenεionε ex¬ tending along εaid y axiε and said z axis respectively, said x axis intersecting said y-z plane at a center point there¬ of, said generator having a point source situated on said x axiε and extending a diεtance from the center of rotation of 0 εaid object equal to an SRAD diεtance, εaid scintillation screen extending a distance on the opposite side of said object along said x axis from said object's center of rota¬ tion equal to a DRAD distance, said object having a y diε¬ tance extending along said y axis and a z distance extending along said z axis; εaid generator haε a finite, circular εource of diamet¬ rical distance, FSS, centered on said x axiε at a diεtance from the center of rotation of εaid object equal to εaid SRAD diεtance, εaid poεitioning means operable to position said object at a distance on said x axis between said finite εource and εaid εcintillation device εuch that a voxel hav¬ ing as small a dimension aε R can be imaged in three dimen¬ sions by only one revolution of εaid object when the ratio of R divided by εaid DRAD diεtance is equal to the ratio of εaid FSS diameter divided by εaid DRAD diεtance added to said SRAD distance.

21. The εystem of claim 19 wherein said εyεtem is ori¬ entated along x, y and z axes perpendicular to one another with orthogonal planes pasεing through any two of εaid axis; said scintillation screen iε εituated in a plane pass- ing through εaid y-z axis and having y and z dimensions ex¬ tending along εaid y axiε and said z axis respectively, said x axis intersecting said y-z plane at a center point there¬ of, said generator having a point source εituated on εaid x axiε and extending a diεtance from the center of rotation of εaid object equal to an SRAD diεtance, εaid scintillation εcreen extending a distance on the opposite side of εaid object along said x axiε from εaid object'ε center of rota¬ tion equal to a DRAD distance, εaid object having a y dis¬ tance extending along said y axis and a z diεtance extending along εaid z axiε; εaid detector means further includes a plurality of detectors optically connected to said scintillation screen, each detector recording light photon energy corresponding to a digitized number in said array, each detector capable of recording light photon energy striking an area correlated to an area on said scintillation screen equal to a minimum diε¬ tance of DS in the y or z direction, εaid positioning means operable to position said object at an SRAD distance such that a voxel having aε small a dimension of R can be imag- ined in three dimensions by only one revolution of εaid ob¬ ject when the ratio of R divided by εaid SRAD diεtance is equal to the ratio of said DS diεtance divided by εaid SRAD diεtance added to εaid DRAD diεtance.

22. The εyεtem of claim 21 wherein said generator has a finite source of diametrical distance, FSS, such the ratio of R divided by εaid DRAD diεtance iε equal to the ratio of εaid FSS diameter divided by εaid DRAD diεtance added to said SRAD diεtance and εaid poεitioning meanε iε operable to select the largeεt of the two SRAD diεtances.

23. The system of claim 1 wherein said point source of said generator is centered along an x axis and situated at a predetermined distance from said object and operable to pro¬ duce a plurality of transmitted beams of radiation emanating from said point εource in generally εtraight lineε which define a three dimenεional fan εhaped array of transmitting radiation beams; said scintillation screen centered with respect to said x axis and extending along a y and a z axis perpendicular to one another and to said x axis for generating visible light in responεe to the energy level of attenuated radiation beamε impacting thereon; a plurality of detectorε arranged in a generally ordered array correlated in poεition to said y and z axiε, each detector operable to generate an analog signal indicative of the light energy transmitted thereto from said scintillation screen; and dynamic flux integration meanε for narrowing the variation between the analog signals generated by said detectors within said array to enhance the resolution of the image produced by said imaging means, said dynamic flux integration means including means for integrat¬ ing over a time period said analog signalε generated by said detector and means for varying said time period correlated to the masε density of said object at any given angular ro¬ tation such that a longer integrating time is provided when the maεε denεity of εaid object penetrated by εaid radiation over a predetermined volumetric portion iε higher than the maεε denεity of said object at another predetermined volu¬ metric position, and εaid imaging means correlated to said positioning means to adjust the digitized number of εaid detectors in reεponεe to εaid time integration.

24. The εystem of claim 23 further including dynamic flux variation means effective to uniformly vary the inten¬ sity of transmitting beams of radiation which strike as at¬ tenuated beams of radiation εaid scintillation screen in said y and z direction, said intenεity of εaid beamε corre¬ lated to the mass denεity of εaid object along said x axis as said object rotates about a y axis such that the intensi¬ ty of the transmitting beams paεεing through high maεε den¬ sities of said object at a specific angular rotation is higher than the beam intensity pasεing through low maεε por¬ tions of said object at a different angular rotation whereby the energy levels of the attenuated beams striking εaid scintillation device are at a lesεer variance than that which would occur had the intenεity of εaid tranεmitting beamε been uniform; and εaid imaging meanε correlated to εaid dynamic flux variation means and effective to adjust said digitized num¬ bers in accordance with the variation in intensity of εaid tranεmitting beamε of radiation.

25. The syεtem of claim 23 wherein εaid detector means includes a two dimenεional detector array developing a plurality of analog signals, each signal indicative of the energy of the light photons emitted from said scintillation screen at discrete locations in said array; and εaid object iε positioned by εaid poεitioning meanε to rotate along a predetermined path about an axis extending through εaid object such that the object iε poεitioned cloε- est to εaid scintillation device when said cone beam paεεeε through the largest mass volume portion of said object.

26. The syεtem of claim 25 wherein εaid rotating meanε iε effective to rotate said object along a generally ellip¬ tical path between εaid generator and εaid detector meanε, said elliptical path having, by definition, a major axiε and a minor axis, said major axis correlated to the largeεt dia¬ metrical distance through the object and said minor axis correlated to the smallest diametrical distance through said object whereby said detector means is not subjected to vari¬ ations in light intensity otherwise possible during its ro- tation to improve image resolution; and means aεεociated with εaid rotation means and said digitizing means to cor¬ rect εaid digitized numbers for the distance of εaid gener¬ ally elliptical path.

27. The syεtem of claim 25 wherein said positioning means initially locates said object at a position between said generator and εaid detector meanε εuch that εaid ini¬ tial εhadow image produced by said detector means represents substantially the complete crosε-section of said object in a two dimenεional spatial relationship; said imaging means effective to construct a two dimensional image of εaid ob¬ ject cr-reεponding to said shadow image; operator means for manually selecting a portion of εaid croεε-εectional image for volumetric viewing; εaid poεitioning meanε responsive to actuation of said operator means to move said object closer to said generator to increase the magnification and enhance the resolution of εaid detector means, and εaid im¬ aging means effective to construct a volume image of said object encompassing only said selected two dimensional por¬ tion of said object.

28. The syεtem of claim 27 wherein εaid εyεtem iε ori¬ entated along x, y and z axes perpendicular to one another with orthogonal planes paεsing through any two of said axis; said scintillation εcreen iε εituated in a plane pass- ing through said y-z axis and having y and z dimensionε ex¬ tending along εaid y axis and said z axiε reεpectively, said x axis intersecting εaid y-z plane at a center point there¬ of, εaid generator having a point εource εituated on said x axis and extending a distance from the center of rotation of said object equal to an SRAD diεtance, εaid scintillation screen extending a distance on the opposite side of said object along said x axis from said object's center of rota¬ tion equal to a DRAD distance, εaid object having a y diε¬ tance extending along εaid y axis and a z distance extending along εaid z axiε; εaid generator haε a finite, circular εource of diamet¬ rical diεtance, FSS, centered on εaid x axis at a distance from the center of rotation of said object equal to said SRAD distance, εaid poεitioning meanε operable to poεition said object at a distance on said x axis between said finite source and said scintillation device such that a voxel hav¬ ing as small a dimension as R can be imaged in three dimen¬ sions by only one revolution of said object when the ratio of R divided by said DRAD diεtance iε equal to the ratio of εaid FSS diameter divided by εaid DRAD distance added to said SRAD diεtance.

29. The εyεtem of claim 27 wherein εaid system is ori¬ entated along x, y and z axes perpendicular to one another with orthogonal planes paεεing through any two of εaid axiε; said scintillation screen is εituated in a plane paεε- ing through εaid y-z axiε and having y and z dimenεions ex¬ tending along said y axis and said z axis reεpectively, εaid x axis intersecting said y-z plane at a center point there¬ of, said generator having a point source εituated on εaid x axiε and extending a diεtance from the center of rotation of said object equal to an SRAD distance, said scintillation screen extending a distance on the opposite side of εaid object along said x axiε from εaid object's center of rota¬ tion equal to a DRAD distance, εaid object having a y diε¬ tance extending along εaid y axiε and a z diεtance extending along εaid z axiε; εaid detector meanε further includes a plurality of detectorε optically connected to said scintillation screen, each detector recording light photon energy corresponding to a digitized number in said array, each detector capable of recording light photon energy striking an area correlated to an area on said scintillation screen equal to a minimum diε¬ tance of DS in the y or z direction, said poεitioning means operable to position said object at an SRAD diεtance such that a voxel having as small a dimension of R can be imag- ined in three dimensionε by only one revolution of εaid ob¬ ject when the ratio of R divided by εaid SRAD distance iε equal to the ratio of εaid DS diεtance divided by said SRAD distance added to said DRAD distance.

30. The εyεtem of claim 29 wherein said generator has a finite source of diametrical distance, FSS, such the ratio of R divided by εaid DRAD diεtance iε equal to the ratio of εaid FSS diameter divided by said DRAD distance added to said SRAD distance and said positioning means is operable to select the largest of the two SRAD distanceε.

31. A computerized tomographic industrial radiation εyεtem for conεtructing a three dimenεional transparent image of at leaεt a portion of an induεtrial part or εimilar object compriεing: a point εource generator for generating a non-pulεed, three dimenεional cone beam of transmitted rays of hard ra¬ diation; collimator means associated with said generator for controlling the cone angle and the peripheral configuration of said cone beam; positioning means for locating said object in the path of εaid cone beam εuch that a predetermined volumetric por¬ tion of said object is exposed to said three dimension cone beam of hard radiation; two dimensional detector means fixed with respect to said point source generator and located on the opposite side of εaid object for recording the attenuated radiation, εaid detector meanε including a scintillation screen receiving attenuated radiation and converting said radiation through scintillation into a two dimensional shadow image and digi¬ tizing meanε for converting said two dimenεional εhadow im¬ age into a ordered array of digitized numberε, each digi¬ tized number in εaid array correεponding to the energy level of an attenuated beam of radiation at a given location in εaid array; εaid poεitioning meanε including means for positioning εaid object relative to said source and means for rotating εaid object relative to said point source and said detector means about only one axis of said object through predeter- mined angular increments, as said object moves by εaid de¬ tector means; means for recording said digitized numbers while said object iε rotating and linearly moving past εaid detector means; and imaging means for constructing a three dimenεional transparent image of said predetermined volumetric portion from said digitized number after a predetermined number of angular rotationε whereby said three dimensional image can be rapidly constructed.

32. The tomographic system of claim 31 wherein said syεtem imageε a plurality of moving objectε on a continuouε basis.

33. The εyεtem of claim 32 wherein εaid εcintillation screen iε dimenεionally εized to εpan a plurality of objectε and εaid cone beam is dimenεionally sized to irradiate sub¬ stantially the entire area of said screen when a plurality of objects are simultaneously imaged.

34. The εyεtem of claim 33 further including timing means coordinated with the speed of said objectε and their rotation for identifying each object and controlling εaid digitizing meanε.