US3082321A

US3082321A - Apparatus for tomography

Info

Publication number: US3082321A
Authority: US
Publication date: 1963-03-19
Anticipated expiration: 1980-03-19

Description

March 19, 1963 P. LE G0 APPARATUS FOR TOMOGRAPHY 2 Sheets-Sheet 1 Filed July 22, 1955 March 19, 1963 P. LE G6 APPARATUS FOR TOMOGRAPHY 2 Sheets-Sheet 2 Filed July 22, 1955 United States Patent 3,082,321 APPARATUS FOR TOMOGRAPHY Pierre Le G6, 112 Rue de Maubeuge, Paris, France Filed July 22, 1955, Ser. No. 523,891 Claims priority, application France Aug. 10, 1954 3 Claims. (Cl. 250-615) The present invention relates to apparatus for tomography and is more particularly directed to means for carrying into effect the methods of automatic and high-speed tomography of the kind described by the present applicant in his French patent of the 18th February 1954 for Improvements in Methods and Devices for Radiography.

An object of the invention is the creation of an apparatus which enables a series of tomographic sections to be obtained automatically in as short a time as possible by means of an arrangement of simple and economic construction which is easy to use.

The apparatus in accordance with the invention comprises, in the :known manner, an oscillating equipment constituted by an X-ray generating unit and a photographic unit arranged respectively at the two extremities of a telescopic arm pivotally mounted on an axis which defines the plane of the section and a mechanism for driving the said oscillating equipment with a to-and-fro motion which displaces the two units in opposite directions along straight line trajectories parallel to the said plane. The apparatus 7 is especially remarkable in that the driving mechanism for the oscillating system is constituted by a connecting rod and crank system, the crank of which is fixed on the shaft of a motor running at constant speed, the connecting rod being coupled to either of the two units of the oscillating equipment which are guided by usual means along their straight-line trajectories.

By virtue of this arrangement, a continuous and regular movement of the oscillating system is obtained, following a sinusoidal law of motion, on either side of a mean position: the passage in one direction or in the other from this mean position is effected at a speed which is determined by the speed of rotation of the motor, whilst the deceleration, the change in direction and the acceleration of the movement at the two extremities of the trajectory of each unit are perfectly progressive. The active periods of emission of the X-ray generator and of exposure of the photographic unit correspond to the passages between two positions chosen at equal distances on each side of the mean position, whilst the intermediate periods are utilised for the changing of the image, that is to say the displacement of the film in the photographic unit.

The speed-s of displacement of the X-ray generator unit and the photographic unit will thus not be constant but will decreaseon each side of the mean position; calculation and experience have shown however, that these variations in speed, with the condition that a certain useful angle is not exceeded, are small in practice and they are not only not troublesome but on the contrary, by their nature they tend to improve the quality of the images obtained.

The invention also contemplates alternative forms of construction of the driving mechanism, which alternative forms enable a uniform speed of displacement of the X-ray generator unit and the photographic unit to be obtained in case of need, or which may result in other more favourable eventual laws of movement, for example motions of constant acceleration or deceleration.

In accordance with one preferred form of embodiment, the axis of oscillation, and in consequence the position of the plane of section, is held fixed in space, the displace ment of section with respect to the subject being effected by movement of the said subject; this movement may be chosen with advantage to be continuous, since the for- 3,682,321 Patented Mar. 19, 1963 ward movement carried out during the period of an expo sure remains of the order of the thickness of section.

On the other hand, the invention also contemplates an extension of the apparatus described to tomoscopy, in such manner as to permit of the use of the high speed of exploration obtained for the production of an immediate view of the image of the section moving in depth from one side to the other of the subject under examination.

The special features and advantages of the invention will furthermore be brought out in the course of the description which follows below of one example of embodiment, reference-being made to the attached diagrammatic drawings in which:

FIG. 1 is a view in elevation of an apparatus in accordance with the invention.

FIG. 2 is a detail view relative to an alternative form of construction of the driving mechanism.

FIG. 3 shows in diagrammatic form, a method of embodiment of a tomoscopic system.

FIG. 4 is a similar View relative to a further form of tomoscopic device.

In accordance with the form of embodiment chosen and shown in FIG. 1, the apparatus comprises an X-ray generator unit 1 and a photographic unit 2 mounted on the two extremities of a telescopic arm 3 pivoted on a fixed axis 4. Since the units 1 and 2 are guided by any known means so as to follow the trajectories XX and Y-Y, which are vertical in the present case, the plane of tomographic section is the plane Z-Z which contains the axis 4.

The subject to be examined is placed on a support 5 in the form of a trolley to which can be imparted a continuous movement at right-angles to the plane of section Z-Z, for example by means of a screw 6 coupled to a motor 7 and engaged in a threaded sleeve 8 rigidly fixed to the said trolley. This movement may be made non-continuous if it is so desired, for example by adding a mechanical or electro-magnetic clutch between the screw 6 and the motor '7, the clutch being controlled by the electrical device which ensures the completion of exposure of one negative and the beginning of the next following.

The photographic unit 2 is coupled by means of a connecting rod 10 to a crank 11 which is itself keyed on the shaft of a motor 12 of the constant speed type, the speed being adjustable. Along the circle shown in chain-dotted lines, which corresponds to the trajectory of the crank pin, there will be in succession an active rising period AB (the rotation being supposed to be in the direction of the hands of a watch), an intermediate period BC, an active falling period CD, and a second intermediate period DA. The active periods extend over an angle of rotation a on each side of the mean position at which the arm 3 and the crank 11 are horizontal. If t is the duration of an active period, t is that of an intermediate period and T is the duration of one revolution of the motor; taking for example a=45, then t=t'=T/4. If the motor is rotating for example at 300 revolutions per minute, then T=0.2 sec- 0nd, and r=z=50 milli-seconds.

The linear speed of the X-ray generator and the photographic unit during the period of emission of X-rays varies, in these conditions by about 29% between the mean position and the points A, B, for example, from the beginning and from the end of the active travel. The influence of this variation in speed on the quality of the tomographic negative is substantially nil, since the extreme positions and thus the lowest speeds correspond to the greatest differences between the source of X-ray emission and the sensitive surface of the photographic unit, whilst at the central position at which the speed is a maximum, this corresponds to the minimum distance between the source of X-rays and the sensitive surface of the photographic plate. The X-ray energy received per unit of time by this plate is thus greater at this moment than at the extreme positions, but as the displacement is faster, the energy received as a function of the linear displacement remains substantially constant.

One method of operation consists in applying the hightension to the X-ray generator unit during each of the rising or falling active periods, and in causing the film to be changed in the photographic unit during each of the intermediate periods; this enables the maximum rate of operation to be obtained and gives, in the case of the numerical example cited, section images per second. As the speed of movement of the subject is regulated to one centimetre per second, there will be obtained under these conditions a succession of 60 section images in 6 seconds, the images being spaced apart by one millimetre.

It is, of course, also possible to apply the high-tension to the X-ray unit, not during each active period but only once for every 2: periods, and this, if the other conditions remain the same as those indicated above, will give a space between successive sections of 2, 3, 4 n millimetres, whilst maintaining the same thickness of section and the same time of exposure of 50 milli-seconds for each tomograph.

The control of the high-tension circuit of the X-ray unit 1 on the one hand, and of the winding mechanism for the film in the photographic unit on the other hand, in dependence on the movement of the crank and rod system, or more generally of the movement of the oscillating equipment, does not lead to any difficulty at all and thus will require no further description.

In the foregoing description also, no details have been given of the construction of the photographic unit, which has no direct bearing on the real object of the invention; it is however clear that photographic units provided with an intensity amplifier find an especially useful application in this case by reason of their qualities of lightness and sensitivity which enable the inertia of the oscillating equipment to be considerably reduced, and in consequence the speed of operation may be substantially increased. The photographic apparatus may then be constituted by a camera of the cinema type or by a more simple photographic apparatus using films of any desired size (7 x 7 cm. for example) with the proviso that the film can be wound forward between each exposure.

On the other hand, the invention is in no way limited to the use of a rod and crank system per se, and any other similar mechanism adapted to convert a circular movement to a reciprocating motion may be substituted therefor. Thus, in order to obtain a constant speed of move ment, for example during the active period of each cycle, recourse may be had to the alternative form of mechanism shown in FIG. 2, in which the crank-pin 14, forming the pivotal mounting of the crank-arm 10 on the driving crank 11, is arranged to slide in a slot provided in the crank instead of being fixed to the said crank. The crank-pin is urged by a compression spring against a cam 16 fixed with respect to the driving shaft 17. The profile of this cam Will be designed in such manner for example, that the speed of displacement of the X-ray unit and the photographic unit is constant during the active period and the rates of acceleration and deceleration are constant during the inactive periods of each cycle, corresponding to the reversals in direction of the movement and to the forward movement of the film.

The tomographic equipment in accordance with the invention and as described above, has important practical advantages as compared with previously known types of tomographic equipment, and especially in that it permits of a very rapid sequence of images to be obtained, the speed of which is such that the definition of the successive images is substantially unaifected by any movement of the subject or patient, such as for example when breathing during examination of the lungs, thus enabling a valid comparison to be obtained between the successive images forming the sequence of the corresponding sections.

FIG. 3 shows a form of embodiment of a tomoscope in accordance with the invention. The optical unit 2' comprises an intensity amplifier, and the photographic device provided (a simple photographic apparatus or a camera of the cinematograph type) is removed from the unit and is replaced by a telescopic dark chamber (of the bellows type or with telescopic tubes), which couples the moulded optical unit 2 to a fixed viewing chamber 21. The image (which is supposed in this case to be formed by parallel rays) produced in the unit 2', is transferred through two total-reflection prisms or

mirrors

22, 23, to a small monocular or binocular observation microscope 24, the position of which is fixed in space, for example by rigid coupling to the fixed frame of the apparatus.

The arrangement shown in FIG. 4 permits of the transmission of images formed by beams of divergent or convergent rays, by virtue of the fact that the length of the optical path between the unit 2' and the fixed viewing chamber 21 is maintained constant in spite of the movehand to the unit 2' and, on the other hand, to the viewing chamber 21, the slider being constantly urged towards the base by a control spring 30. The image produced by the intensity-amplifier unit 2' is transmitted by the totalrefiection prisms or

mirrors

31, 32, 33 and 34, and it is easy to see that the length of the optical path followed remains constant in the present case, whatever the movements of the unit 2 may be, these movements being followed by the dark chamber at half their amplitudes. The dark chamber is in this case coupled on the one hand to the unit 2 and to the viewing chamber 21 on the other hand, by two

bellows members

35, 36, or by suitable corresponding telescopic tubes.

In addition to the advantages of the apparatus of the present invention in automatic tomography, as already referred to, the very rapid sequence of images obtained also makes possible the use of automatic tomoscopy, the sequence being adapted to create a clear, static visual image, due to persistence of vision, as in the technique of cinematography. By this means, it becomes possible to observe visually the various tomographic sections of the subject under examination, as the subject is moved at right-angles across the plane comprising the real or virtual axis of oscillation, such as the axis 4 of FIG. 1.

What I claim is:

1. An apparatus for automatic tomoscopy comprising: an X-ray generating unit; an optical receiver including a fixed viewing chamber and a movable optical unit, a lightproof dark chamber coupled between said fixed chamber and said movable unit, an optical system of total-refiection devices for transferring the image from said movable optical unit to said fixed viewing chamber; means for guiding said X-ray unit and said movable optical unit along laterally spaced straight guides; means for continuously oscillating the two said units in opposite parallel directions along said guides at such a high speed that a static visual image, due to persistence of vision, is obtained in said fixed viewing chamber when the X-ray unit is operated during a fraction of its travel in either direction; and means for impressing movements on said optical system of total-reflection devices which are similar to the movements effected to said movable optical unit but of half their respective amplitudes, whereby the total length of the optical path between said movable optical unit and said fixed viewing chamber remains constant,

notwithstanding the displacements impressed on said movable optical unit.

2. An apparatus as claimed in claim 1, and further comprising supporting means for the subject under examination, and means for continuously displacing said supporting means during the tomoscopic examination, the direction of the displacement being perpendicular to the direction of motion of the said units.

3. An apparatus :as claimed in claim 1, in which the total-reflection optical system forms an optical path of invariable length between said movable optical unit and said fixed viewing chamber, said optical system being contained in the dark chamber and carried by a sliding member adapted to move with substantially no play along slide-tracks parallel to the direction of movement of said movable unit, said sliding member being suspended from a cable, the extremities of which are respectively fixed to said movable unit and said fixed viewing chamber, said cable passing round a pulley rigidly fixed to the said sliding member, the latter being urged in a direction opposite to that of the movement of said movable unit by means of a control spring.

References (Zited in the file of this patent UNITED STATES PATENTS 2,000,497 Pohl May 7, 1935 2,110,954 Grossmann Mar. 15, 1938 2,353,145 Chamberlain July 11, 1944 2,490,400 Berggren Dec. 6, 1949 2,491,224 Stava Dec. 13, 1949 2,522,280 Kollmorgen Sept. 12, 1950 2,812,687 Ei'tel et al Nov. 12, 1957 FOREIGN PATENTS 910,716 Germany May 6, 1954

Claims

1. AN APPARATUS FOR AUTOMATIC TOMOSCOPY COMPRISING: AN X-RAY GENERATING UNIT; AN OPTICAL RECEIVER INCLUDING A FIXED VIEWING CHAMBER AND A MOVABLE OPTICAL UNIT, A LIGHTPROOF DARK CHAMBER COUPLED BETWEEN SAID FIXED CHAMBER AND SAID MOVABLE UNIT, AN OPTICAL SYSTEM OF TOTAL-REFLECTION DEVICES FOR TRANSFERRING THE IMAGE FROM SAID MOVABLE OPTICAL UNIT TO SAID FIXED VIEWING CHAMBER; MEANS FOR GUIDING SAID X-RAY UNIT AND SAID MOVABLE OPTICAL UNIT ALONG LATERALLY SPACED STRAIGHT GUIDES; MEANS FOR CONTINUOUSLY OSCILLATING THE TWO SAID UNITS IN OPPOSITE PARALLEL DIRECTIONS ALONG SAID GUIDES AT SUCH A HIGH SPEED THAT A STATIC VISUAL IMAGE, DUE TO PERSISTENCE OF VISION, IS OBTAINED IN SAID FIXED VIEWING CHAMBER WHEN THE X-RAY UNIT IS OPERATED DURING A FRACTION OF ITS TRAVEL IN EITHER DIRECTION; AND MEANS FOR IMPRESSING MOVEMENTS ON SAID OPTICAL SYSTEM OF TOTAL-REFLECTION DEVICES WHICH ARE SIMILAR TO THE MOVEMENTS EFFECTED TO SAID MOVABLE OPTICAL UNIT BUT OF HALF THEIR RESPECTIVE AMPLITUDES, WHEREBY THE TOTAL LENGTH OF THE OPTICAL PATH BETWEEN SAID MOVABLE OPTICAL UNIT AND SAID FIXED VIEWING CHAMBER REMAINS CONSTANT, NOTWITHSTANDING THE DISPLACEMENTS IMPRESSED ON SAID MOVABLE OPTICAL UNIT.