US3930162A

US3930162A - Matrix-form radiation image converter

Info

Publication number: US3930162A
Application number: US367144A
Authority: US
Inventors: Karl-Hans Reiss
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 1972-06-21
Filing date: 1973-06-05
Publication date: 1975-12-30
Anticipated expiration: 1992-12-30
Also published as: DE2230329A1

Abstract

An image converter is used to make visible images produced by gamma rays or similar penetrating rays like X-rays, etc., by transforming the distribution of ray density contained in a bundle of rays carrying the image which is to be made visible, by means of a cathode and an anode spaced from the cathode. The space between the electrodes contains a gas and the electrodes are subjected to a voltage which produces electrical discharges during ray penetration at corresponding locations depending upon the rays. The cathode as well as the anode consist of a plurality of parts having large surfaces which extend at least approximately perpendicularly to the ray incoming surface of the converter, so that the electric field extends parallel to this surface. The invention is particularly characterized in that the gas is under pressure in the range of 10 at., that the applied voltage makes certain the operation in the proportional range and that parts of the anode and of the cathode are combined in rows. Rows of the cathode elements and those of the anode extend at an angle to each other, the rows being connected electrically with a device for forming an electronic intensity center which produces representable local signals for orientation of the discharge bundle striking the anode.

Description

United States Patent 1 Reiss Dec. 30, 1975 MATRIX-FORM RADIATION IMAGE CONVERTER [75] Inventor: Karl-Hans Reiss,Erlangen,

Germany [73] Assignee; Siemens Aktiengesellschaft, Munich,

Germany 22 Filed: June 5,1973

21 Appl. No.: 367,144

Primary Examiner-James W. Lawrence Assistant Examiner-Davis L. Willis Attorney, Agent, or FirmV. Alexander Sher [57] ABSTRACT An image converter is used to make visible images produced by gamma rays or similar penetrating rays like X-rays, etc., by transforming the distribution of ray density contained in a bundle of rays carrying the image which is to be made visible, by means of a cathode and an anode spaced from the cathode. The space between the electrodes contains a gas and the electrodes are subjected to a voltage which produces electrical discharges during ray penetration at corresponding locations depending upon the rays. The cathode as well as the anode consist of a plurality of parts having large surfaces which extend at least approximately perpendicularly to the ray incoming surface of the converter, so that the electric field extends parallel to this surface. The invention is particularly characterized in that the gas is under pressure in the range of 10 at that the applied voltage makes certain the operation in the proportional range and that parts of the anode and of the cathode are combined in rows. Rows of the cathode elements and those of the anode extend at an angle to each other, the rows being connected electrically with a device for forming an electronic intensity center which produces representable local signals for orientation of the discharge bundle striking the anode.

6 Claims, 4 Drawing Figures US. Patent Dec. 30, 1975 Sheet10f2 3,930,162

Fig.3

Fig.2

U.S. Patant Dec. 30, 1975 Sheet 2 of2 3,930,162

MATRIX-FORM RADIATION IMAGE CONVERTER This invention relates to an image converter for making visible images produced by gamma rays or similar penetrating rays like X-rays etc. by transforming the distribution of ray intensity contained in the cross-section of the ray bundle carrying the image which is to be made visible, into an image of discharge by means of a cathode and an anode spaced from the cathode. The space between the electrodes contains a gas. The electrodes are subjected to a voltage which produces electrical discharges at locations which are struck by the rays. The cathode as well as the anode consist of a plurality of parts the large surfaces of which extend at least approximately perpendicularly to the ray striking surface of the converter, so that the electrical field extends parallel to this surface.

Devices of this type are used in the art to change invisible images produced by ionizing rays like gamma rays, X-rays etc. into a form suitable for evaluation.

Known image converters of this type were provided as a substitute for spark image converters wherein the electrodes are plates subjected to electrical voltage and having large surfaces extending opposite each other. Between these plates a visible spark discharge takes place depending upon the rays. The electrical field then extends parallel to the rays which strike the plates perpendicularly. The efficiency is small, however, since the path of the rays in the gas filling the space between the electrodes, is small and thus their absorption is small, A quantum change in the range of :1 is the rule. A better construction of this type is described in the German Pat. No. 1,764,905 which refers to electrodes consisting of several parts the arrangement of which has the effect of small tubes having parallel axes and located next to each other with the counter electrode located in the center. In devices of this type the path of the rays can be increased when the end openings of the tubes are located upon a surface which receives the image producing rays. Then the electrical field extends transversely, so that as compared to the above-mentioned spark chamber with unchangeable layer thickness concerning electrical properties (distance cathode-anode), the layer thickness as concerns ray incidence, namely, the absorption is increased several times depending upon the length of the tube.

A drawback of the known image converting device is that the quantum output is only small, particularly for the localization and representation of gamma ray results, as they take place in isotope diagnosis. For these purposes other complicated devices have been introduced, as for example, the so-called Anger-camera. As is known, in this camera signals are produced by several electronic multiplying sections from scintillations produced in a luminous layer by ray actions which are to be made visible, the signals corresponding to the electronic intensity point structure.

An object of the present invention is to provide a device which can serve as a gamma camera and which can produce by substantially simpler means ray products and images which are at least comparable to those of the Anger-camera.

Other objects will become apparent in the course of the following specification.

In the accomplishment of the objectives of the present invention an image converter is used which makes visible images produced by gamma rays or similar penetrating rays by transforming the distribution of ray intensity in a ray bundle carrying the image to be made visible into a discharging image by means of a cathode and a spaced anode. The space between the electrodes contains a gas and the electrodes are subjected to a voltage which produces electrical discharges during ray penetration at the corresponding locations depending upon the rays. The cathode and the anode consist of a plurality of parts having large surfaces which extend at least approximately perpendicularly to the ray receiving surface of the converter, so that the electrical field extends parallel to this surface. The present invention is particularly characterized in that the gas is under pressure in the size of 10 at., that the applied voltage makes certain the operation in the proportional range and that parts of the anode and the cathode are combined in rows, with the rows of the cathode elements and those of the anode extending at an angle to each other. The rows are connected electrically with a device for forming an electronic intensity center which produces image-like local signals for orientation of the discharge bundle striking the anode.

Despite a somewhat higher expense for the operation in proportional range due to the height of the signal, there is the advantage that in case ofa quantum output comparable to the Anger camera and a certain discrimination of impulses, a more precise localization is produced. The construction is much more simple. No scintillation layer is required, which usually consists of a single crystal, and it is not necessary to use many electronic multiplier stages.

Measurements which have been actually carried out have shown that, due to the high absorption of a gas such as xenon at about 10 at., high quantum output can be expected. The upper pressure limit is based primarily upon the firmness of the inlet surface and lies at about 20 at.. If, for example an absorption thickness of the gas layer of 10 cm is used, the following quantum efficiencies have been calculated for xenon subject to a pressure of 10 at.:

Xe keV 89% Te keV 37% I 360 keV 13% The above amounts do not consider the release of electrons at the metal surface of the inlet window. There an additional effect of l to 2% can take place. Iodited hydrocarbons can be also used as similarly acting gases. Pressure must lie in the above-mentioned range, since the number of molecules per unit volume is proportional to pressure.

According to a preferred embodiment of the present invention the casing of the converter consists of a pressure-tight container the side walls and the bottom of which consist of steel A collimator can be placed at the ray inlet surface which diminishes the effects of contrast diminishing stray rays. As is known, it consists of a honeycomb structure the openings of which extend in the direction of incoming rays and which is limited by walls having a thickness of 2 to 4 mm, which mostly consist of lead. The openings with a depth of'6O mm have a diameter of 6 mm. The inlet window for the rays, i.e., the closing of the openings of the collimator at their limit to the pressure tight container, consists of a ray transmitting substance, such as titanium. The cover can be pulled in the form of a foil which is 1 to 2 mm thick upon the ray outlet openings of the collimaent invention provides that the little tubes and the inner conduits which act as electrodes should be combined into n rows and n columns and guided upon 2n passages. An additional guide can be used for a capacitively coupled signalling plate. This arrangement provides n image prints.

Known devices, including the Anger camera, have provided different solutions for the discrimination and local representation of appearing impulses. One of them is described by Kullander and assistants in the publication Nuclear Instrum. Meth. 92 (1971 no. 1, page 141. When this device is used within the framework of the present invention the rows and sections of the tube arrangement are guided upon transit chains. When an impulse arrives it produces initially a starting signal upon a signalling plate. With this starting signal two clocks are started which determine the running time of a chain for the x direction and the y direction. These running times are used as a measure for the coordinates and can be used for representation upon an oscillograph. The impulse height ofeach impulse is independently examined by a discriminator. Thus only those impulses are counted to which the discriminator was set, namely those the height of which corresponds to the required gamma energy. The representation can take place in a known manner upon a display device or in a magnetic core matrix.

The invention will appear more clearly from the following detailed description when taken in connection with the accompanying drawings showing by way of example only, preferred embodiments of the inventive idea.

In the drawings:

FIG. 1 is a diagrammatic view showing a spark chamber of the present invention provided with honeycombed cathodes.

FIG. 2 shows in perspective a part of the device of FIG. 1 and illustrates specifically the hexagonal crosssection of the tubes in the longitudinal axes of which the anodes in the shape of round pins are located.

FIG. 3 shows in perspective a constructively simple device of the present invention wherein the cathodes are plateshaped and the anodes are introduced as rods in the spaces between these plates.

FIG. 4 is a circuit diagram of an electronic switch arrangement for determining gravity points of spots which are struck by rays according to the device of the present invention.

FIG. 1 shows a pressure-tight chamber 1 provided with faucets la and 1b and containing anodes 2 lying at the positive pole of the source 3 of direct voltage. The negative pole of the source 3 is connected with the cathode 4 consisting of a plurality of little tubes combined in rows which are electrically insulated from each other transversely to the rows by intermediate layers 5 of mica which are 0.2 mm thick. The little cathode tubes are produced from adjacently located strips 7 which are 100 mm wide and consist of brass or heavy metal sheets 0.30 mm thick (FIG. 2), which have a profile of alternately raised and pressed down portions each in the shape of one half hexagon. When the sheets are placed together hexagonal tubes of honeycomb structure are produced with a diameter of 6 mm. The anode is placed in the shape of rods 8 in the longitudinal axis of the hexagonal tubes and is held at the beginning and end of the tubes by insulating

pieces

9 and 10 of acrylic glass. In the tubes of the cathode 4 there is a gaseous atmosphere consisting of xenon for the introduction, refilling or exchange of which in the space of the casing 1 there are provided

openings

9a and 10a in the holding

pieces

9 and 10 at the beginning and end of the cathode tubes.

When voltage is applied for operation in the proportional range, in the present case about 8 kV, and when ionized rays strike in the direction of arrows 6, at those locations wherein rays drop into the tubes there is a discharge depending upon the number of absorbed quantum. These discharges produce signals which are tranformed into a visible picture in the analyzing device 10' the details of which are shown in FIG. 4.

FIG. 3 shows an embodiment of the present invention which is particularly advantageous due to its simple construction wherein the cathode consists of plates 11 placed next to each other. The plates have a width of mm, a thickness of 0.3 mm and consist of a metal middle ordinal number, in this case nickel. The plates 11 have a spacing of 3 mm which is maintained at upper and lower edges of the plates by

space holders

12, 13 of insulated plastic, namely, acrylic glass. The plastic holds metal rods 14 which are the anodes, with their longitudinal axes parallel to the plates 11 and to each other. The rods at their lower ends extend through the holders 13 and at their upper side are connected to the insulating holder 12. The rods 14 consist of rust free steel, have a circular cross-section with a diameter of 1 mm and a length which corresponds to the plate width up to about 0.5 mm. The applied voltage amounts to about 6 kV.

The operation of the embodiment of the present invention shown in FIG. 3 is substantially the same as that of the construction of FIGS. 1 and 2. The sole difference is that in the construction of FIG. 3 no separate tubes are formed. In this construction also the rays penetrate through the cathode plates 11 and the anode rods 14 into the intermediate space which is the gas chamber filled in this construction with xenon and subjected to a pressure of 8 at..

The strips 7 of FIGS. 1 and 2 or the plates 11 of FIG. 3 form a longitudinally extending cathode constituting a row over which the image area runs. Transversely thereto extend the electrical connecting lines 15 to 20 of the rods 8 and the connecting lines 21 to 29 of the rods 14 (FIG. 3). The connections of the cathodes are indicated by numerals 30 to 33 in FIG. 2 and by numerals 34 to 36 in FIG. 3. It is apparent that when the lines 15 to 20 are connected with lines 30 to'33 and the lines 21 to 29 are connected with lines 34 to 36 the derived values can produce significant x-y signals indicating the section of the rows by corresponding arrangement of specific strips 7 or plates 11 and a specific row of pins 8 or 14. Since these signals follow one after the other it I is also possible to produce a discrimination of the height of individual signals in a known manner.

The determination of the striking location of the ray spot or its center takes place according to FIG. 4 in gamma cameras in a manner known per se by analogous gravity point formation. For better clarity of illustration FIG. 4 shows only a few of the electrode rows present in the described example and corresponding to lines to and 30 to 33, as well as lines 21 to 29 and 34 to 36; the rows are indicated in FIG. 4 as 37 to 41 and 42 to 46. They are connected by high ohmic resistances 47 and 48 with corresponding source 49 of direct voltages. As shown in FIG. 4, the discharges produced by the ray bundle penetrating into the spot 50 are collected in the rows 37 to 41 and in rows 42 to 46 extending transversely thereto. These discharges are strengthened in charge receiving amplifiers 51 to 55 and 56 to 60 to form signals capable of further treatment. The signals X, which pertain to i rows 42 to 46, the amount of which corresponds to part of the charge carriers from the spot 50 collected on one side, are considered in a coordinate network 61 corresponding to the location of the pertaining electrode strip, i being the number of continuously counted rows while x is the x-coordinate. During the examination a factor a, is impressed upon the signal X,- from the resistances 62 to 71 with the use ofa voltage divider. By a suitable selection of resistances 62 to 71 the factors a,- form discrete coordinate values of corresponding rows 1' in the x direction. As suitable selection resistances are here used produced by voltage dividers the ratio of which corresponds to a,- and results in i/i Here i is the running number of strips and i is the greatest available number of strips. Furthermore the sums of both resistances of each voltage divider are equal.

The examined signals a x are summed up in a sum amplifier 72. A signal 2 a x is produced; then after division in the quotient former 73 by the sum signal of all untreated signals x,- produced in the sum amplifier 74 the following normed local signal results:

2 n x, E x,-

In the presented example the X-signal and the Y-signal formed in corresponding manner by the use of anode rows 37 to 41 in coordinate network 75 (identical to 61) are supplied to the imaging element 76 of an X-Y oscilloscope and are brightly felt by a Z signal which is produced by impulse high discrimination of untreated sum signal 2 x; in one channel discriminator 77. Then the gravity point of the spot 50 ofa ray bundle striking the devices of FIGS. 1, 2 or 3 is produced in the XY diagram of the element 76. This corresponds to the 6 location in the device of the original absorption location of a gamma quanta of the energy determined by the discriminator 77, so that the desired visible representation is produced.

I claim:

1. A proportional radiation image converter for making visible images produced by gamma rays, comprising a container having a ray inlet surface and, inside the container, in combination, a matrix of detector cells, said matrix comprising two groups of conductors, the conductors of one group being anode members and spaced from the conductors of the other group which are cathode members, the space between the groups being filled with gas having substantially a pressure of 10 at., the conductors in the groups forming rows with rows of the one group extending at an angle to the rows of the other group, the conductive member of the group belonging to cathode members substantially encircling one of the conductors of the other of said groups, and thus forming one of said cells extending substantially perpendicularly to the ray inlet surface, and means for separately detecting an electrical signal from each of said conductors and for indicating the cell address of a gas-ionizing incident in the detector; said cathode members comprising electrically conductive strips which are insulated from one another; said anode members comprising electrically conductive rods disposed between and insulated from said cathode members.

2. An image converter according to claim 1, wherein the rows of cathode members and the rows of anode members extend at right angles to each other.

3. An image converter according to claim 1, wherein said means comprise an impulse high disciminator.

4. The device of claim 1, wherein said cathode strips are in the form of flat plates.

5. The device of claim 1, wherein said cathode strips each have the cross-section of a half of a hexagon with said strips confronting one another so that said half hexagonal configurations confront one another to define a full hexagonal shape; said anode rods being disposed at the center of each of said hexagonal tubes defined by said half hexagonal cross-sectional shapes of said cathode strips.

6. The device of claim 1, wherein each of said cathode strips has a width of from to millimeters and wherein said strips are separated from one another by a distance of from 3 to 6 millimeters.

Claims

6. The device of claim 1, wherein each of said cathode strips has a width of from 90 to 100 millimeters and wherein said strips are separated from one another by a distance of from 3 to 6 millimeters.