GB1587846A - Production of x-ray images - Google Patents

Abstract

In an electron-radiographic imaging camera, in order to obtain an image which reaches on one side up to the edge of the imaging camera, such as is required, e.g., for the purposes of mammography, the dielectric sheet (15) intended for recording the electrostatic, latent image is bent at the relevant side over the electrode edge (12a). The electrode edge is pressed together with the sheet against seals (21-24) which bear in the region of the bending edge against the bent-over part of the sheet. The electrode (12) on which the dielectric sheet is laid and which is preferably spherically curved can be inserted into a part of the imaging camera which supports the other electrode (10, 39) and the seals (21-24, 34a, 34b). The seals are realised as pressure-supported seals. <IMAGE>

Description

(54) IMPROVEMENTS IN AND RELATING TO THE PRODUCTION OF X-RAY IMAGES (71) We, AGFA-GEVAERT AKTIENGESELLSCHAFT, a body corporate organised according to the laws of the Federal Republic of Germany, of Leverkusen, Federal Republic of Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to the production of X-ray images.

It has previously been proposed to use, for the production of X-ray images, an image chamber which has its walls formed by an anode and a cathode electrode, each of which is spherically curved about a centre point located at the source of X-rays. Each electrode is arranged on a part of the image chamber which is connected to the other part in a gas-tight manner by means of a seal. During the imaging operation, a gas having a high atomic number is enclosed in the space between the electrodes at a pressure which is higher than atmospheric pressure, and during its irradiation electrons are liberated which cause electrical charges corresponding to the radiation image to be deposited on a dielectric sheet resting against one of the two electrodes.

Processes of this kind are, for example, the subject of German Offenlegungsschrift Nos. 24 34 557 and 22 58 364. Owing to the sealing frame which is required in both cases between the upper and lower parts of the image chamber, however, it is not possible to make X-ray exposures extending up to the edge of the image chamber, as is required, for example, for mammographic purposes. In this case the X-ray image of the female breast must also include the areas of the breast adjoining the rib-cage, if diagnostic requirements are to be fulfilled. This is not possible with an image chamber surrounded with the sealing frame which is usual in electron-radiographic image chambers.

The invention provides an image chamber for the production of X-ray images, comprising a pair of electrodes spaced apart from one another, and sealing means arranged, in operation, to seal the region between the electrodes from the region outside the electrodes, one of the electrodes being so arranged that an edge portion of an image support sheet resting on it can wrap around an edge of the electrode and the sealing means being arranged along that edge to contact the said edge portion of the image support sheet and not to extend between the electrodes, so that the imagereceiving area in that vicinity can extend up to the edge of the electrode.

The invention also provides a method of producing X-ray images, which comprises positioning a dielectric image support sheet on the said one electrode of an image chamber according to the invention and exposing the image chamber to a source of X-rays, the arrangement being such that a charge image is produced on the record sheet.

With the arrangement of the invention it is possible to obtain an image extending right up to the edge of the image chamber on one side. Owing to the fact that the sealing means rests, in operation, against the part of the image support sheet which is bent round the electrode in the region of the image edge in question, this bending edge can come right up to the outer limit of the image chamber. As will be explained in greater detail hereinafter, the sealing means can then either rest from the underside of the electrode against the part of the image support sheet bent round the electrode, or the turned-over edge of the sheet can press into a sealing groove which can be constructed in a very space-saving manner.

Advantageously, the said one of the electrodes on which the image support sheet rests, in operation, is removable from the remainder of the image chamber.

In one advantageous arrangement, a sealing bar rests in each case against the inserted electrode from above on three sides and from below on the leading side seen in the direction in which the electrode is pushed in, and the seals are preferably in the form of so-called pressure-supported seals in which the application of a sealing lip is intensified by the pressure of the medium which is to be sealed off.

In order that it should not be possible with this sealing arrangement for any leakage to occur even at the outer corners of the electrode through the seals which press on the electrode from below and from above the lower sealing bar is preferably connected to the upper sealing bars by means of two sealing strips resting against the leading edge, in the direction of insertion, of the push-in electrode.

The image support sheet may rest against the furthest of the two electrodes, which are preferably spherical, from the source of radiation, and this electrode may be so arranged on the push-in support that the leading areas of the electrode, seen in the direction in which it is pushed in, run approximately parallel to the latter direction, and the remaining areas of the curved electrode are increasingly inclined with respect to the direction of insertion. A clamping bar is preferably provided for the rear edge of the image support sheet, seen in the direction of insertion, and the leading edge of the electrode in this direction has a projecting rim for the anchorage of the turned-over edge of the image support sheet.

According to another advantageous arrangement of the invention, the inserted electrode pushes the fold of the image sheet bent round the leading edge of the electrode, seen in the direction of insertion, into a sealing groove and pushes the remaining edges of the sheet against sealing bars, which are preferably in the form of pressure-supported seals.

The image support sheet may rest against the electrode adjacent to the source of radiation in the operating state, and a flat supporting surface for the image support sheet adjoin the spherical electrode surface, the supporting surface simultaneously forming the sealing plane.

A clamping device is preferably provided to fix at least one side edge of the sheet, and the other electrode, which is also preferably spherical, is capable of being pivoted out of the path of the push - in electrode holder.

Advantageously, a contact which can be closed by the insertion of the electrode holder is provided between the electrode covered by the image support sheet and the current supply of the electrode.

X-ray apparatus and two forms of image chamber constructed in accordance with the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a perspective view of X-ray apparatus according to the invention, which is suitable for mammography; Figure 2 is a portion of the apparatus of Figure 1 on a larger scale; Figure 3 shows a section through a first form of image chamber according to the invention; Figure 4 shows a portion of the image chamber of Figure 3; Figure 5 shows a section through a second form of image chamber according to the invention; and Figure 6 shows a portion of the image chamber of Figure 5.

With reference to the accompanying drawings, in Figure 1, an X-ray tube 2 with its shield 3 and also an image chamber 4 are mounted on a pivotable support 1. Near the actual examination unit, a conditioning device 5 and a developing apparatus 6 are also set up. In the conditioning device 5 dielectric foils to be introduced into the developing chamber can be discharged. In the developing apparatus a latent electrostatic image applied to the foil in the image chamber 4 can be rendered visible by means of electrostatically-attractable toner. A holder 7 with a dielectric foil tensioned on it as shown in Figure 2, details of which will be described more fully hereinafter, can be inserted into openings 5a and 6a of the conditioning device and of the developing apparatus, respectively, and into the image chamber 4.

According to Figure 3, in the housing 4 of the image chamber is arranged a beryllium plate 8 which is very rigid and at the same time has a relatively high degree of permeability to X-rays. Beneath the beryllium plate 8 there is a moulded portion 9 of a material having a relatively low specific gravity, for example polyurethane or acrylic foam, which carries a spherical electrode 10. The moulded portion 9 also offers only a very low resistance to the X-rays. The electrode 10 is connected to an electrical potential of suitable magnitude by means of a pin 11 projecting laterally from the image chamber. In the case of the electron-radiographic process in question, the potential applied between the electrodes ranges in the order of magnitude of approximately 10 - 15 kv.

Over the beryllium plate 8 and a front wall 4c of the chamber housing 4 there is also arranged a protective layer 50, for example, composed of plastics or lacquer, which protects the patient from contact with any live parts of the apparatus, and also from contact with the beryllium plate and other metal parts of the apparatus.

The above-mentioned holder 7 can be pushed by way of a guide surface 4a into the housing 4 of the image chamber. The holder 7, which for the sake of easier handling is preferably made of plastics, carries a further spherical electrode 12. The electrode 12, when pushed into position, is connected to the external potential by way of a contact spring 13 and a contact pin 14. The electrode 10 which is rigidly fixed in the housing 4 is preferably connected to earth and the electrode 12 is connected to the voltage.

A portion 12a of the electrode 12 projects slightly on the leading side in the direction of insertion A of the holder 7. A leading portion of a dielectric sheet 15, which consists of a flexible plastics material, for example Mylar (Registered Trade Mark) or PET, is turned-over around the projecting portion 12a. It has been found that in spite of its elasticity, the dielectric sheet 15 is stiff enough to remain anchored by its sharply bent edge 15a behind the projecting portion 12a without any further retaining means.

When its other margin is fixed by means of a clamping bar 16, the sheet is securely attached to the holder 7 and assumes the position shown in Figure 3. The clamping bar 16 is tightened by means of a wire clip 17 extending through an aperture 7a in the holder 7 and anchored by a pin 20 of a tensioning lever 19 supported on a spindle 18 of the holder 7. The spindle 18 is so arranged in relation to the anchorage pin 20 that in the tensioning position shown, in which the lever 19 comes to rest inside the aperture 7a. the dead centre of the tensioning movement has just beem passed. so that the tensioning position or the clamping of the bar 16 is maintained bv the resilient force of the wire clip 17.

As soon as the holder 7 is introduced into the chamber housing 4 by using a portion 7b which acts as a handle. it is pushed by means of a locking device. which will be described in more detail hereinafter. in the direction of the arrow A against sealing bars 21 - 24 arranged in the image chamber housing 4.

The sealing bars 21. 2' and 24 rest from above against the electrode 12 with the interpolation of the dielectric sheet 15.

whilst the sealing bar 23 presses from below against the projecting section 12a of the electrode with the interpolation of the turned-over portion 15a of the dielectric sheet. The sealing bars 21 to 24 together enclose an image-receiving area of the sheet 15.

As can be seen from Figure 4. the sealing bar 23 is connected to the sealing bars 22 and '4 at the corners of the gas space by means of a sealing strip 23a in each case. In the Figure, all surfaces which are connected to the adjacent walls in a gas-tight manner by means of adhesive or the like are indicated by hatching. It can be seen that the electrode 12, including the dielectric sheet 15, must be pushed in the direction of the arrow A against these sealing strips 23a.

Without the sealing strips there would be produced along the front edge and the side edge of the electrode 12 a path to the open, unsecured by a sealing strip or a gas-tight glued joint, for gas contained inside the image chamber at a raised pressure.

The holder 7 is pressed in the direction of the arrow A by a wedge-shaped lug 25a which is attached to a disc 25 supported on a spindle 26 in the image chamber housing 4.

The disc 25 can be rotated in the direction of the arrow by means of an external handle 27 so that the lug 25a exerts a wedge-like action behind a projection 7c of the holder 7. The locking of the holder 7 brought about by means of the lug 25a is also necessary to prevent the holder 7 being pushed out of the housing 4 as a result of the internal raised pressure in the image chamber.

In order to initiate the imaging operation, when the holder 7 is inserted process gas is introduced at a raised pressure into the space above the foil 15 by means of a gas duct 29. 30 which has an external connecting nipple which is not visible in the Figure. In the case of a mammographic unit, in which relatively weak X-ray irradiation is used, inert gases, for example xenon. krypton, or freon are preferably used, at a pressure of 620 at.

Under the influence of the gas pressure produced in the space between the foil 15 and the electrode 10, the foil 15 fits itself against the spherical electrode 12. The air which still remains between the foil 15 and the electrode 12 escapes to the open by way of a duct 7e in the holder 7, and also by way of a duct 4b in the housing 4 which is aligned with the duct 7e when the holder 7 is pushed into the chamber. The electrons liberated in the process gas by the X-ravs during the subsequent imaging operation. or the ions produced during this operation. as a result of the spherical shape of the electrodes 10.

12 and of the dielectric sheet 15. are able to produce on this sheet a sharply focussed, undistorted image of the radiation image in the form of an electrostatic charge image, which can be converted into a visible toner image in the developing apparatus 6.

If in the case of a mammographic exposure. for example. the rib-cage of the patient rests against the front edge 4c of the image chamber of the corresponding part of the protective layer 50. then the area of the foil 15 which is usable for image data (the image-receiving area) extends to within a few millimetres of the rib-cage of the pa tient. This advantage is due to the fact that the sealing bar 23 arranged in this region presses from underneath against the projecting part 12a of the electrode 12, with the turned-over part 15a of the foil interpolated, and does not prevent the portion of the sheet 15 on the upper surface of the project ing portion 12a from receiving the change image.

On completion of the imaging operation, the gas pressure in the space between the electrodes 10 and 12 is reduced to normal atmospheric pressure again. The foil, which is held on one side by the turned-over portion 15a and on the other side beneath the clamping bar 16, returns to its initial position. The image distortion which occurs remains within acceptable limits, since as a result of the clamping of the foil on both sides the transverse stretching necessary to obtain the required foil shape during the irradiation operation is distributed approximately uniformly over the entire foil area.

With reference to the second form of image chamber shown in Figure 5, there is attached to the housing 4 of the image chamber a beryllium plate 31 which is provided with a pressure transfer layer 32 composed of a relatively pressure-resistant material, for example polyurethane or acry lic foam, which is, however, easily pene trated by the X-rays. The layer 32 forms part of the guiding and retaining means for a foil holder 33 which can be pushed into the housing 4 and which in turn rests on a support surface 4a in the housing 4.

Attached to the guide surface 4a there is a seal 34 which on three sides forms a frame of pressure-supported seals 34a and on the fourth side provides a sealing groove 34b.

On the underside of the holder 33 a spherically-curved support surface 33a for an electrode 35 is formed. The electrode 35 is connected to a pin 36 which projects laterally out of the holder 33 and, when the holder 33 is pushed into the housing 4, touches a contact spring 37 provided in the insertion channel for the holder 33. The contact spring 37 produces the contact between the electrode 35 and its current supply.

On a spindle 38 of the housing 4 con nected electrically tq earth, a further spher ically-curved electrode 39 is supported against which there rests a pressure piece 40 rivetted to the seal 34. Beneath the pressure piece 40, the housing 4 has a recess 4d which is connected by way of a connecting nipple 41 and a pipeline 42 to a pressure gas supply, for example a pump. The operating pressure in the pipeline 42 is somewhat higher than the operating pressure in the space between the electrodes 35, 39.When this pressure is applied to the pipeline 42, the seal 34, arches up fairly high over the recess 4d, so that the pressure piece 40 attached at this position and resting against the electrode 39 pivots the latter into its operating position 39', shown by broken lines, in which stop lugs 39a of the electrode rest against a supporting surface 33b of the holder, and the two electrodes are separated by the distance d which is necessary during the actual imaging operation.

In order to determine the initial state of the dielectric sheet 15, the latter, as can be seen especially in Figure 6, is bent over on one side of the electrode 35 with an edge strip 15a bending round an edge 33c of the holder 33. The bending edge of the sheet is pressed by means of the pressure device 25-27 in the direction of the arrow A, into the sealing groove of the sealing bar 34b. A clamping bar 16 with the corresponding actuating mechanism 17-29 is again provided for the outer edge of the dielectric sheet. The actuating mechanism 17-20 is in this case arranged in a recess 33d in the holder 33.

After the clamping operation, the dielectric sheet 15 assumes the initial position 15' indicated by dash/dotted lines in Figure 5. If the process gas is now blown at a raised pressure into the space between the seal 34 and the dielectric sheet 15 by way of a connecting nipple 43 which passes through the floor of the housing 4 and the seal 34, and which is attached to the housing 4 by means of a screw 44 and connected to the gas system of the apparatus by means of a pipeline 45, the dielectric sheet 15 fits itself against the spherically-curved electrode 35 and against the transition section 33b between the spherically-curved electrode surface and the flat sealing surface.The air originally enclosed in the space between the intital position 15' of the dielectric sheet 15 and the electrode 35 can escape into the open through a borehole 33e in the holder 33 by way of the recess 33d in the holder and a duct 4e in the housing. After the gas pressure in the space between the electrodes has been reduced, the flexible dielectric sheet assumes its initial position once more.

With this arrangement again, the area of the foil 15 that can be filled with image data (the image-receiving area) extends close to the outer wall or the outer protective layer 50 of the image chamber.

WHAT WE CLAIM IS: 1. An image chamber for the production of X-ray images, comprising a pair of electrodes spaced apart from one another, and sealing means arranged, in operation, to seal the region between the electrodes from the region outside the electrodes, one of the electrodes being so arranged that an edge portion of an image support sheet resting on it can wrap around an edge of the electrode and the sealing means being

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (25)

1. **WARNING** start of CLMS field may overlap end of DESC **.

   tient. This advantage is due to the fact that the sealing bar 23 arranged in this region presses from underneath against the projecting part 12a of the electrode 12, with the turned-over part 15a of the foil interpolated, and does not prevent the portion of the sheet 15 on the upper surface of the project ing portion 12a from receiving the change image.

   On completion of the imaging operation, the gas pressure in the space between the electrodes 10 and 12 is reduced to normal atmospheric pressure again. The foil, which is held on one side by the turned-over portion 15a and on the other side beneath the clamping bar 16, returns to its initial position. The image distortion which occurs remains within acceptable limits, since as a result of the clamping of the foil on both sides the transverse stretching necessary to obtain the required foil shape during the irradiation operation is distributed approximately uniformly over the entire foil area.

   With reference to the second form of image chamber shown in Figure 5, there is attached to the housing 4 of the image chamber a beryllium plate 31 which is provided with a pressure transfer layer 32 composed of a relatively pressure-resistant material, for example polyurethane or acry lic foam, which is, however, easily pene trated by the X-rays. The layer 32 forms part of the guiding and retaining means for a foil holder 33 which can be pushed into the housing 4 and which in turn rests on a support surface 4a in the housing 4.

   Attached to the guide surface 4a there is a seal 34 which on three sides forms a frame of pressure-supported seals 34a and on the fourth side provides a sealing groove 34b.

   On the underside of the holder 33 a spherically-curved support surface 33a for an electrode 35 is formed. The electrode 35 is connected to a pin 36 which projects laterally out of the holder 33 and, when the holder 33 is pushed into the housing 4, touches a contact spring 37 provided in the insertion channel for the holder 33. The contact spring 37 produces the contact between the electrode 35 and its current supply.

   On a spindle 38 of the housing 4 con nected electrically tq earth, a further spher ically-curved electrode 39 is supported against which there rests a pressure piece 40 rivetted to the seal 34. Beneath the pressure piece 40, the housing 4 has a recess 4d which is connected by way of a connecting nipple

   41 and a pipeline 42 to a pressure gas supply, for example a pump. The operating pressure in the pipeline 42 is somewhat higher than the operating pressure in the space between the electrodes 35, 39.When this pressure is applied to the pipeline 42, the seal 34, arches up fairly high over the recess 4d, so that the pressure piece 40 attached at this position and resting against the electrode 39 pivots the latter into its operating position 39', shown by broken lines, in which stop lugs 39a of the electrode rest against a supporting surface 33b of the holder, and the two electrodes are separated by the distance d which is necessary during the actual imaging operation.

   In order to determine the initial state of the dielectric sheet 15, the latter, as can be seen especially in Figure 6, is bent over on one side of the electrode 35 with an edge strip 15a bending round an edge 33c of the holder 33. The bending edge of the sheet is pressed by means of the pressure device 25-27 in the direction of the arrow A, into the sealing groove of the sealing bar 34b. A clamping bar 16 with the corresponding actuating mechanism 17-29 is again provided for the outer edge of the dielectric sheet. The actuating mechanism 17-20 is in this case arranged in a recess 33d in the holder 33.

   After the clamping operation, the dielectric sheet 15 assumes the initial position 15' indicated by dash/dotted lines in Figure 5. If the process gas is now blown at a raised pressure into the space between the seal 34 and the dielectric sheet 15 by way of a connecting nipple 43 which passes through the floor of the housing 4 and the seal 34, and which is attached to the housing 4 by means of a screw 44 and connected to the gas system of the apparatus by means of a pipeline 45, the dielectric sheet 15 fits itself against the spherically-curved electrode 35 and against the transition section 33b between the spherically-curved electrode surface and the flat sealing surface.The air originally enclosed in the space between the intital position 15' of the dielectric sheet 15 and the electrode 35 can escape into the open through a borehole 33e in the holder 33 by way of the recess 33d in the holder and a duct 4e in the housing. After the gas pressure in the space between the electrodes has been reduced, the flexible dielectric sheet assumes its initial position once more.

   With this arrangement again, the area of the foil 15 that can be filled with image data (the image-receiving area) extends close to the outer wall or the outer protective layer 50 of the image chamber.

   WHAT WE CLAIM IS: 1. An image chamber for the production of X-ray images, comprising a pair of electrodes spaced apart from one another, and sealing means arranged, in operation, to seal the region between the electrodes from the region outside the electrodes, one of the electrodes being so arranged that an edge portion of an image support sheet resting on it can wrap around an edge of the electrode and the sealing means being

   arranged along that edge to contact the said edge portion of the image support sheet and not to extend between the electrodes, so that the image-receiving area in that vicinity can extend up to the edge of the electrode.
2. 2. An image chamber as claimed in claim 1, wherein the image-receiving area is defined, except along the said edge of the electrode, by the sealing means.
3. 3. An image chamber as claimed in claim 1 or claim 2, wherein the said one of the electrodes is removable from the remainder of the chamber.
4. 4. An image chamber as claimed in any one of claims 1 to 3, wherein the electrodes are each of substantially spherical curvature, and the centres of curvature of the electrodes are arranged to coincide, at least in operation.
5. 5. An image chamber as claimed in any one of claims 1 to 4, wherein the outer edge of each electrode defines a rectangle.
6. 6. An image chamber as claimed in claim 5 when dependent on claim 3, wherein the said one of the electrodes is so arranged that a portion of an image support sheet resting on it can wrap around its edge on the leading side of the electrode on insertion into the remainder of the image chamber.
7. 7. An image chamber as claimed in claim 6, wherein the said one of the electrodes is provided with a projecting rim along its leading side for the image support sheet to extend around.
8. 8. An image chamber as claimed in claim 6 or claim 7, wherein the sealing means comprises a first portion arranged to bear against the said one of the electrodes on the surface of the electrode facing the other electrode except along the leading side where a second portion of the sealing means is arranged to bear against the surface of the electrode facing away from the other electrode.
9. 9. An image chamber as claimed in Claim 8, wherein the first portion of the sealing means is connected by sealing strips to the second portion.
10. 10. An image chamber as claimed in Claim 8 or Claim 9, wherein the first and second portions of the sealing means are each in the form of a pressure-supported seal having a sealing lip arranged to bear against the image support sheet on the said one of the electrodes, the arrangement being such that the sealing lip is urged against the image support sheet, in operation, by the pressure of the gas within the region between the electrodes sealed from the exterior.
11. 11. An image chamber as claimed in any one of Claims 1 to 10, wherein the said one of the electrodes is the electrode which, in operation, is furthest from the source of radiation.
12. 12. An image chamber as claimed in Claim 11, when dependent on Claim 3, wherein the arrangement is such that the leading area of the surface of the electrode, on insertion, extends approximately parallel to the direction of insertion and the remaining area is increasingly inclined with respect to the direction of insertion.
13. 13. An image chamber as claimed in any one of Claims 1 to 12, wherein there is provided means for clamping the image support sheet outside the image-receiving area.
14. 14. An image chamber as claimed in claim 13 when dependent on Claim 3, wherein a clamping bar is provided for the rear side of the image support sheet, on insertion.
15. 15. An image chamber as claimed in any one of Claims 1 to 6, wherein the sealing means is provided with a groove in the vicinity of the edge of the electrode around which the image support sheet is arranged to wrap and the said one of the electrodes is arranged to urge the said edge portion of the image support sheet into the groove.
16. 16. An image chamber as claimed in Claim 15, wherein, for enclosing the remainder of the image-receiving area and sealing the said region, the sealing means comprises a pressure-supported seal having a sealing lip arranged to bear against an image support sheet on the said one of the electrodes, the arrangement being such that the sealing lip is urged against the image support sheet, in operation, by the pressure of the gas within the region between the electrodes.
17. 17. An image chamber as claimed in any one of Claims 1 to 6, or Claim 15 or Claim 16, wherein the said one of the electrodes is the electrode which, in operation, is nearest to the source of radiation.
18. 18. An image chamber as claimed in Claim 17, wherein the said one of the electrodes is adjoined by a substantially flat supporting surface for the image support sheet which forms the sealing plane, and wherein there is provided clamping means for clamping a portion of the edge of an image support sheet.
19. 19. An image chamber as claimed in Claim 17 or Claim 18, wherein the other of the said electrodes is pivotably mounted so that it can be moved out of the path of removal and insertion of the said one of the electrodes.
20. 20. An image chamber as claimed in claim 3 or any one of claims 4 to 19 when dependent on claim 3, wherein there is provided an electrical contact which can be closed by the insertion of the said one of the electrodes for electrically connecting the electrode to a voltage supply.
21. 21. An image chamber substantially as hereinbefore described with reference to, and as shown in, Figures 1 to 4 or Figures 5 and 6 of the accompanying drawings.
22. 22. An image chamber as claimed in any one of claims 1 to 21, in combination with a source of radiation;
23. 23. A method of producing X-ray images, which comprises positioning a dielectric image support sheet on the said one electrode of an image chamber as claimed in any one of claims 1 to 21 and exposing the image chamber to a source of X-rays, the arrangement being such that a charge image is produced on the record sheet.
24. 24. A method as claimed in claim 23, wherein the X-rays ionise a gas of high atomic number in the sealed space between the electrodes, and an electric field produced by a potential difference between the electrodes causes electrons and/or ions produced by the ionisation to come into contact with the image support sheet to produce the charge image.
25. 25. A process for the production of X-ray images substantially as hereinbefore described with reference to the accompanying drawings.