FR2634029A1 - Equipment for producing radiological images - Google Patents

Abstract

Equipment for producing radiological images from memory scintillator plates. According to the invention, such a memory scintillator plate 11 is first subjected to a sensitisation treatment under the action of a radiation source 25, before being packaged so as to be placed in a case 28 which is opaque to daylight but transparent to X-rays; after radiography, the plate is removed from its case and read by a sensor 36, whilst being excited by a pulse generator 38. Application to scientific X-ray diffraction.

Description

"Equipment for the development of radiological images"
The invention relates to equipment for the preparation of radiological images, more particularly designed to be used in connection with a conventional or pre-existing X-ray irradiation installation. The invention mainly makes it possible to replace the usual photographic films with scintillating plates with memory, which can be reused and which furthermore promotes digital image processing and their archiving in modern computer systems.

 The use of components capable of memorizing a radiological image (obtained for example by a conventional operation of irradiation with X-rays) and of restoring it in the form of visible radiation is known and explained for example in the French patent application N '86 .O2876 deposited on February 28, 1986. The use of such components makes it possible to replace the usual photographic films.

In addition to its high cost price, the photographic film lends itself poorly to subsequent image processing requiring digitization of said image from a complex device such as a microdensitometer.

 It has therefore been proposed to use a screen forming a memory scintillator plate to replace the film. Such a screen is for example made up of a thin layer of a phosphor material the opposite faces of which are covered with electrodes, (at least one of them being transparent), capable of being connected to a source of voltage to subject the phosphor material to an electric field. Said phosphor material is capable of absorbing the energy conveyed by the X-ray beam (and therefore of memorizing a radiological image if said beam has passed through an element or organ to be radiographed) and then of releasing this energy in the form of an emission. luminous, in response to the application of an appropriate electric field. The image thus produced can be captured by a camera or any other suitable image sensor, delivering information usable for a video display and / or any desirable digital processing. .

 Depending on the case and in particular the energy of the incident X-ray beam, the phosphor material can be chosen from doped sulphides. The phenomenon is known as the GUDDEN AND POHL effect.

 The invention relates to an application of this technology to radiology, in particular by the use of small scintillating memory plates, comparable to those of films used in X-ray diffraction.

In this spirit, the invention therefore essentially relates to equipment for the production of radiological images, characterized in that it comprises:
- at least one memory scintillator plate,
a unit for sensitizing said plate including a source of radiation and means for conditioning said plate in order to place the latter in an envelope opaque at least to radiation of wavelengths of the visible spectrum and,
- a unit for reading said plate including an image sensor and a generator of reading pulses intended to be connected to electrodes of said plate.

 The memory scintillator plate is made of a scintillator material of the kind indicated above, in powder form and incorporated in a binder such as a transparent synthetic resin. The mixture is deposited in the form of a thin layer and the two parallel faces of this layer are covered by two electrodes, at least one of which is transparent.

 Thus, the equipment defined above is designed to be used in conjunction with a conventional X-ray irradiation facility. The user, for example the person responsible for producing X-ray diffraction images therefore uses the scintillator plates in exactly the same way as the x-ray films presented in a package, which he had until now. The memory scintillator plate is therefore placed in its support, for example in an X-ray diffraction device and, after X-ray irradiation, the image is "developed" in said reading unit and displayed on a television set. It is also possible to carry out digital processing on the data representative of the image, in order to better highlight certain details.

Archiving on computer memory becomes possible and advantageous.

The sensitization unit of the scintillator plate very significantly increases the conversion factor X photons / visible photons. It has indeed been observed that the intensity of the light emission of the type
GUDDEN AND POHL depends in particular on the previous lighting conditions: on the plate, the intensity being notably lower if the latter has been kept prolonged in the dark. The radiation source used is preferably a source of radiation emitting mainly in the ultraviolet range.

The consequence of this treatment is to increase the number of available "traps" responsible for the effect
GUDDEN AND POHL and capable of being "filled" during X-ray irradiation. A model giving a satisfactory explanation of the GUDDEN AND POHL effect from the presence of such "traps" was given in the article by PROSKURA entitled "Participation of the recombination barrier in the storage of excitation by ZnS: Cu crystal phosphor" published in Opt. Spectrosc. (USSR), Vol. 42, N6 page 645 of 1977.

 It should be noted that this process cannot in any way be compared to an erasure of the memory plate.

Known x-ray imaging devices use a memory scintillator plate and an optical or thermal erasure step is implemented in these systems.

During the erasing, the traps filled during the irradiation then incompletely emptied during the reading of the memorized image are then completely emptied, optically or thermally. On the contrary, the envisaged sensitization process aims to increase the number of "traps" available to memorize the image and therefore to obtain a better light output.

 According to another important characteristic of the invention, the aforementioned awareness unit further comprises an electric pulse generator intended to be connected to said electrodes during a process of awareness of a said plate. Thus, during the illumination of the plate with ultraviolet light, voltage pulses are applied between the electrodes, the polarity of which can be positive, negative or preferably alternative.

The application of the corresponding electric field through the sensitive layer is prolonged for a certain time after the ultraviolet illumination, the scintillating plate being kept in the dark. The following justification can be given to this process. Illuminating the plate creates charges.

However, during illumination, the voltage pulses are applied between the electrodes. The first awareness step thus has the consequence of filling the traps located at the periphery with these charges, and on the other hand increasing the number of these traps available. They must therefore be "emptied" to be able to refill them under the effect of radiation
X. For this, the voltage pulses are continued to be applied while the plate is kept in the dark.

 With such a sensitization treatment, the conversion efficiency of X photons / visible photons is multiplied by about twenty.

The invention will be better understood and other advantages thereof will appear more clearly in the light of the description which follows, given solely by way of example and made with reference to the appended drawings in which:
- Figure I is a schematic view of all of the equipment according to the invention; and
- Figure 2 is a schematic sectional view of the memory scintillator plate used in the context of the invention.

 FIG. T represents an apparatus grouping together all the means necessary for raising awareness, for conditioning. and reading memory scintillator plates 11 of the kind indicated above. This equipment therefore essentially comprises a magazine 12 containing a number of scintillator plates 11, an awareness unit 14 and a reading unit 16.

 The awareness unit 14 is arranged in a closed and opaque box 17 so that these elements are protected from daylight. This unit comprises a transport mechanism 18 extending between an outlet from the magazine 12 and an outlet 20 from the shoemaker 17, awareness-raising means 22 and packaging means 23.

Thus, each sensitized and conditioned plate, protected from light in an opaque envelope or case, reaches outlet 20 where it is made available to the user. The awareness means and the packaging means are arranged in this order along the transport mechanism 18 between the magazine 12 and the outlet 20. The awareness means 22 comprise a source of ultraviolet radiation 25, oriented towards a location of predetermined sensitization (defined along the path of the plates) as well as a pulse generator 26 electrically connectable to two electrodes of a scintillator plate 11, when the latter is at said sensitization location. The generator 26 is of the type delivering rectangular pulses, preferably alternating. The conditioning means 23 located downstream of said sensitization location, allow the sensitized plate to be placed in a case 28 opaque to daylight (for example a polymer film ). It is in this packaging that the plate appears at exit 20.

The case 28, made of material transparent to X-rays has the following function:
it keeps the sensitized plate in the dark because it was found that it could be "veiled" by daylight, in particular by the "blue" part of the visible spectrum.

 From the moment a plate is thus delivered to the outlet 20, the user has all the time necessary to carry out an X-ray, in the usual way and using his own radiation irradiation equipment. X.

 The plate is then introduced, via an inlet 30, inside the reading unit 16 which essentially comprises, in a housing, a transport mechanism 32, an extraction device 34 for removing the plate II from its case. 28, an image sensor 36 and a reading pulse generator 38, intended to be connected to the electrodes of the memory scintillator plate when the latter is at a defined reading station along the transport mechanism 32 in look of said image sensor 36. During its passage inside the reading unit 16, a plate It is therefore successively stripped of its case 28, reaches said reading station and is then re-introduced into the magazine 12.

 The image sensor 36 is here advantageously a two-dimensional optical sensor whose reading window has substantially the same shapes and dimensions as those of the scintillator plate. This sensor is placed so as to be opposite the plate II when the latter is at said reading station. The acquisition of the image can therefore be done overall, taking into account the small dimensions of the plate 11. The sensor 36 can advantageously be constituted by a matrix of charge transfer components (better known by the abbreviation CCD). The window of said sensor is constituted by a "wafer" of optical fibers, known per se, directly applied against the scintillator plate 11 to avoid loss of resolution. To do this, said sensor 36 is mounted on a mobile assembly 40, actuated by example by a small pneumatic cylinder 41, allowing it to be brought into direct contact with a plate when the latter is at said reading station. The detector 36 is completed by an image intensifier of known type. The reading pulse generator 38 is very simple, since it is simply designed to deliver, on each reading, two voltage pulses, of opposite polarities. These pulses are applied between the electrodes of the plate. Indeed, the application of this double alternation, between the electrodes, is sufficient to cause the luminescent emission and therefore reveal the radiological image. Of course, the pulse generators 26 and 38 can be combined in the same electronic circuit. The information delivered at the output of the detector 36 is digitized and stored in an interface 45 and the image, possibly processed, is displayed on the screen. of a television appliance 46. The interface 45 can also include or be connected to mass memories capable of storing the digital data representative of the radiographies carried out.

We will now describe, with reference to Figure 2, a currently preferred embodiment of a scintillator plate usable in the context of the invention. This component comprises a rigid substrate 50 transparent to X-rays on which are successively deposited in thin layers: a first aluminum electrode 52, an active scintillator layer 53 and a transparent electrode 54, for example made of tin and indium oxide C ' is the latter which is presented opposite the sensor 36 at the time of reading. The different electrodes 52 and 54 substantially cover the two opposite faces of the active layer 53. However, the electrode 52 has a larger surface than the active layer 53 to allow electrical connection with the pulse generator 26 or 38. active material here is a sulfide of general formula ZnxCdl x S doped with aluminum and copper, silver or gold. The material is reduced to powder and incorporated into a polymeric binder. The thickness of the active layer is preferably between 50 and 200 microns, depending on the energy of the X-rays so as to achieve a good compromise to obtain sufficient absorption of the rays.
X and avoid loss of resolution due to the isotropy of light radiation.

 The practical implementation of the apparatus which has just been described is as follows.

 A memory scintillator plate 11, as illustrated in FIG. 2, is extracted from the magazine 12 and routed to the sensitization station facing the source of ultra-violet radiation 25. At this location, the electrodes are connected to the generator of pulses 26 and the plate is subjected to ultraviolet radiation. This situation is maintained for approximately 30 seconds.

Then, the source of ultraviolet radiation 25 is stopped but the plate remains subjected to the electric field caused by the generator 26 for approximately 30 additional seconds. The plate is then conveyed to the packaging means where it is introduced into a case 28. It is finally conveyed to the outlet 20.

After X-ray radiography, the user introduces the plate through the opening 30. The latter is conveyed to the extraction device 34 where it is stripped of its envelope 28. Then, the plate is placed at the reading station and the moving element 40 is actuated so that the reading window of the sensor 36 is placed in contact with the transparent electrode of the plate. Simultaneously, the pulse generator 38 is connected to the electrodes of said plate. The latter is then electrically excited so as to cause the appearance of the luminescent image which is analyzed globally by the sensor 36.

 The image is then processed and displayed on the television receiver. After reading, the plate 11 is reintroduced into the magazine 12.

 The advantages of the invention appear clearly in the light of the above description. A digital radiological image can be obtained in a few seconds.

This can therefore be processed and stored, allowing rapid analysis. The use of such optical sensors
CCD (associated with an image intensifier) achieves an image quality and sensitivity higher than that of a photographic film. We can therefore consider reducing the dose of X-rays, therefore in particular the exposure time. Finally, the use of a reusable device considerably reduces the operating costs of the radiology system while remaining compatible with a conventional X-ray irradiation installation.

Claims (9)

RESELL CATT. ONS  1- Equipment for the development of radiological images, characterized in that it includes:  - at least one memory scintillator plate (11),  - an awareness unit (14) of said plate including a radiation source (25) and conditioning means (23) of said plate to place the latter in an envelope opaque at least to radiation of wavelengths of the visible spectrum and,  - a reading unit (16) of said plate including an image sensor (36) and a reading pulse generator (38) intended to be connected to electrodes of said plate.  2- Equipment according to claim 1, characterized in that said reading unit (16) comprises an extraction device (34) to disengage said plate from its envelope and place it at a reading station.  3- Equipment according to claim 1, characterized in that said sensitization unit further comprises an electric pulse generator (26), intended to be connected to said electrodes during a sensitization process of a said plate.  4- Equipment according to claim 2 or 3, characterized in that said image sensor (36) is a two-dimensional optical sensor comprising a reading window of dimensions substantially equal to those of said plate and in that it is placed so as to be opposite said plate when the latter is at said reading station.  5- Equipment according to one of claims 2 to 4, characterized in that said two-dimensional optical sensor is formed of a matrix of charge transfer components, called CCDs.  6- Equipment according to claim 5, characterized in that said optical sensor (36) is mounted on a movable assembly (40) enabling it to be brought into contact with said plate when the latter is at said reading station.  7- Equipment according to one of the preceding claims, characterized in that said reading pulse generator (38) is arranged to deliver at least two voltage pulses of opposite polarities.  8- Equipment according to one of the preceding claims, characterized in that said pulse generator (20) of said awareness unit is of the type delivering rectangular pulses, preferably alternative.  9- Equipment according to one of the preceding claims, characterized in that said radiation source (25) of said sensitization unit is of the type emitting mainly in the field of ultza-violets.