US3922547A - Virtual electrode imaging chamber - Google Patents
Virtual electrode imaging chamber Download PDFInfo
- Publication number
- US3922547A US3922547A US530057A US53005774A US3922547A US 3922547 A US3922547 A US 3922547A US 530057 A US530057 A US 530057A US 53005774 A US53005774 A US 53005774A US 3922547 A US3922547 A US 3922547A
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- United States
- Prior art keywords
- electrodes
- electrode
- imaging chamber
- conductors
- gap
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- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
- G03G15/00—Apparatus for electrographic processes using a charge pattern
- G03G15/054—Apparatus for electrographic processes using a charge pattern using X-rays, e.g. electroradiography
- G03G15/0545—Ionography, i.e. X-rays induced liquid or gas discharge
Definitions
- This invention relates to electronradiography and in particular, to a new and improved imaging chamber.
- an x-ray opaque gas is used between two electrodes in an imaging chamber to produce a photoelectric current within the chamber, which current is collected on a dielectric sheet placed on one or the other of the electrodes, resulting in a latent electrostatic image. The latent image is then made visible by xerographic techniques.
- An x-ray source is used to create primary photoelectrons in a gas in the gap between the electrodes of the imaging chamber.
- Typical imaging chambers have planar or cylindrical electrodes and the oblique incidence of the incoming x-ray produces geometric unsharpness in the resultant image.
- the electrodes are constructed in such a manner that the potential variations at the electrode surfaces correspond to that of concentric spherical equipotential in the imaging gap.
- a layer of finite and variable conductivity material is used for each electrode, with the potential applied between the center and periphery of the elec' trodes.
- the present invention contemplates the use of a dielectric substrate with a low conductivity layer at the gap surface of each electrode, which layers may be of uniform thickness and resistivity, with spaced conductors on the substrates and connected to appropriate voltage sources for producing the desired electric field.
- FIG. 1 is a diagramatic illustration of an x-ray system with an imaging chamber incorporating the presently preferred embodiment of the invention
- FIG. 2 is a plan view of one of the electrodes of the chamber of FIG. I;
- FIG. 3 is a schematic of the electrical connections for the chamber of FIG. I;
- FiG. 4 is a perspective view of a cylindrical electrode, illustrating an alternative embodiment of the invention.
- FIG. 5 is a sectional view of an alternative electrode construction
- FIG. 6 is a plan view of another alternative electrode construction
- FIG. 7 is a sectional view taken along the line 77 of FIG. 6 and including a second electrode and an electrical schematic similar to that of FIG. 3;
- FIG. 8 is a perspective view illustrating the use of the round electrode of FIG. 6 in a rectangular configura tion.
- FIG. 9 is a view similar to that of FIG. 4 illustrating a cylindrical embodiment of the electrode of FIG. 6.
- the system as illustrated in FIG. 1 includes an x-ray source 10 positioned for directing radiation to an object II which may rest on a table 12.
- An imaging chamber 13 carrying a dielectric receptor sheet I4 may be positioned below the table, with x rays from the source passing through the object 11 and into the gas-filled gap 15 of the imaging chamber I3.
- the design of the imaging chamber itself is not a feature of the present invention and various of the known imaging chambers may be utilized.
- the imaging chamber may comprise a housing 20 with cover 21 and electrodes 22, 23 mounted therein, defining the gap 15 therebetween. Gas may be introduced into the chamber via line 28, and the electrodes are connected to the power supply via cables 29, 30.
- a preferred embodiment for the electrode 22 is shown in FIG. 2 and comprises a dielectric sheet substrate 31 with a plurality of concentric conductors Rl R7 on one surface of the sheet and a layer 32 of low conductivity material over the conductors. Since most x-ray pictures are rectangular or square, arcuate circular segments are utilized in the corners. While a seven conductor electrode is illustrated in FIG. 2, various numbers of conductors may be utilized depending upon the size of the imaage and on the accuracy of simulation of the sperical potential desired. In one embodiment, a [4 inch by I7 inch image is obtained with electrodes I7 inches by 20 inches and having 15 concentric conductors.
- Means are provided for connecting the conductors RI R7 to a power supply and typically may comprise additional conductors 35 on the opposite surface of the substrate and interconnections 36 through the substrate between the conductors R1 R7 and the conductors 35, with the conductors 35 being connected to the cable 29 for connection to the power supply as illus trated in FIG. 3.
- the electrode 23 may be constructed in the same manner as the electrode 22, with the conductors RI R7 at the gap surface.
- a voltage supply 37 is connected across a voltage divider 38 and another voltage supply 39 is connected across another voltage divider 40.
- the points on the voltage divider 38 are connected to the conductors R1 R7 of electrode 22 by cable 29, and the points on the voltage divider 40 are connected to the conductors Rl R7 of electrode 23 by cable 30.
- Another voltage supply 42 is connected across the electrodes, preferably by being connected to the corresponding conductors on the gap surfaces of the two opposing electrodes, as illustrated in FIG. 3.
- variable resistor 43 may be connected in parallel with the electrode 22 and a variable resistor 44 may be connected in parallel with the electrode 23. Either or both of the resistors 43, 44 may be used to compensate for changes in the distance between the x-ray source It) and the imaging chamber I3, operating in the manner described in detail in copending application Ser. No. 388,262, filed Aug. M, 1973 and assigned to the same assignee as the present application.
- the imaging chamber of the present invention provides the desired spherical equipotentials on the electrodes. with the concentric conductors defining radial locations at which the voltages are applied. A close approximation to the desired condition is achieved by applying the voltages at the spaced locations along the surfaces of the electrodes, with the approximate potential configuration approaching the ideal configuration as the number of conductors on the electrode surfaces is increased. The maximum resolution required in a particular instrument dictates the number of conductor locations on the electrodes.
- the electrode which is on the x-ray source side of the gap desirably should not contain any x-ray absorbing material of a localized nature within the detection capability of the imaging chamber. since this material would appear on the resulting picture. Any uniformly absorbing material over the entire image area would not appear on the final image, but would reduce the net efficiency of the instrument. Therefore, the total x-ray absorption of the electrode 22 and also of the housing cover 21 should be minimized. This problem does not exist with the lower electrode where x-ray absorption is not a factor.
- the substrate is a polyester sheet typically having a thickness in the range of 10 to 14 mils, this material having sufficient dielectric strength and mechanical rigidity.
- the conductors may be applied to the electrode by laminating thin aluminum sheet on both surfaces and then producing the desired conductor configuration by photoetching. Typically the aluminum sheet can be onefourth mil thick.
- the width of the conductors on the electrode 22 should be minimized to avoid the conductors appearing in the final image, and typically the con ductors are in the order of l mils wide. Conductor width is not a problem on the electrode 23, but ordinarily the two electrodes will be identical for ease in manufacturing.
- the interconnections between the conductors on opposite sides of the electrode should also be nonimaging and typically may be a carbon adhesive such as a mixture of lampblack and a polyester adhesive. Of course, other materials and sizes may be used as desired.
- the material used for the low conductivity layer 32 on the substrate 31 may be a carbon impregnated epoxy which is stable and uniform in composition.
- the low conductivity layer may be made separately and at tached to the polyester substrate by a thin film of adhesive or may be applied in fluid form and cured on the substrate.
- the resistivity of the low conductivity layer at the gap surface of the electrode preferably is in the range of about 10 to ohms per square.
- the upper resistivity limit (the lower electrode current limit) is dictated by the desire to have the electrode current greater than the gap current so that fields created by the gap current do not distort the desired spherical field created by the electrodes.
- the lower resistivity limit (the upper current limit) is dictated by the size of the power supplies needed to provide the currents, with higher currents requiring larger power supplies.
- each of the three power supplies may provide outputs in the order of kilovolts, with the parameters chosen such that the current in a voltage divider preferably is in the order of 10 times greater than the current in the 4 connected electrode so as to prevent any variation in divider output due to small changes in conductivity of the electrode between adjacent rings due to variations in manufacturing conditions.
- FIG. 5 An alternative embodiment of the electrode 22 is shown in H0. 5, where the low conductivity layer 32 is formed as two layers 32a and 32b. Layer 32a is on the substrate 31 over the conductors R1 R7, and layer 32b is on layer 32a. Layer 32a is thinner and of higher conductivity than layer 32b.
- the receptor 14 is positioned at the layer 32b which functions to spread the voltage from the conductors and thereby spread or diffuse the conductor image which might result from the conductors being between the receptor and the x-ray source. This problem is not encountered with the electrode 23 and ordinarily there would be no need for the double layer construction for electrode 23.
- the layer 32b desirably is about at least twice as thick as the layer 32a and preferably in the range of 2 to 4 times as thick.
- the layer 32a is in the order of 0.010 to 0.020 inches thick and the layer 32b is in the order of 0.040 to 0.060 inches thick.
- the layer 32b desirably has a resistivity about at least ten times that of the layer 320 and preferably in the range of l0 to times.
- the layer 32a has a resistivity of about 10 to 10 ohms per square and the layer 32b has a resistivity of about l0 to 10 ohms per square.
- the preferred embodiment of the imaging chamber described above has utilized electrodes with flat parallel gap surfaces.
- the present invention is equally applicable to electrodes with concentric cylindrical gap surfaces.
- the relation between the flat parallel gap surfaces and concentric cylindrical gap surfaces is discussed in the aforesaid copending application Ser. No. 388,212.
- a typical cylindrical electrode 23 incorporating the present invention is illustrated in FIG. 4, with parallel conductors 1 7 on the gap surface side of the substrate 31' and connected to conductors 35' on the opposite surface by interconnections 36', with low conductivity layer 32 and with cable 30 providing for connection of the electrode to the voltage divider 40.
- the lower electrode 23' would be concave when viewed from a gap surface while the upper electrode (not shown) will be convex when viewed from the gap surface.
- the electrodes may be manufactured in a flat position and formed to the slightly cylindrical configuration by the housing of the imaging chamber in which they are mounted.
- the edge of a fourteen inch wide cylindrical electrode will be about a millimeter out of plane.
- substantially planar covers both electrodes with both flat parallel gap surfaces and electrodes with concentric cylindrical gap surfaces.
- Electrodes 52, 53 correspond to electrodes 22, 23 of FIG. 1. However, the electrodes are formed with a plurality of concentric sections 55. All the sections 55 are oflow conductivity material, but adjacent sections have different conductivity, with the section conductivity decreasing from the center to the edge of the electrode. The conductivity for each section desirably is substantially uniform throughout the section.
- the electrodes 52, 53 may be of carbon impregnated epoxy in the order of l0 to 14 mils thick, with the resistivity varying from 10 ohms per square at the center to ohms per square at the edge. Typically a 17 inch diameter electrode may have concentric sections.
- the electrodes of FIGS. 6 and 7 do not require the voltage dividers 38, 40 used with the electrodes of FIGS. 1 and 2 having the discrete conductors. Otherwise, the electrical circuitry is substantially the same, utilizing the power supplied 37, 39 and 42.
- a piece of aluminum foil 57 may be affixed at the center of the electrode and a ring of aluminum foil 58 may be affixed at the rim of the electrode for making the electrical connections.
- the shunting resistors 43, 44 may be used if desired.
- the imaging chambers presently in use call for rectangular receptors and rectangular electrodes.
- the circular electrodes of FIGS. 6 and 7 are readily formed into the rectangular configuration, as shown in FIG. 8.
- the electrode 53 is laid onto a dielectric substrate 54, typically a 14 mil thick mylar sheet, of the desired rectangular shape and size.
- the overhanging edges 58 of the electrode are folded over the edge of the substrate 54 and affixed to the reverse side, preferably with a conducting shield, such as a 1 mil aluminum foil, positioned between the edges 58 and the substrate 54.
- the electrode configuration of FIGS. 6 and 7 can be provided in a cylindrical shape.
- a cylindrical electrode 53' with parallel sections 55' is shown in FIG. 9.
- the sections 55' are of low and substantially uniform conductivity, with the conductivity decreasing from the center section to each edge.
- the various parameters set out in the description of the preceding electrodes are applicable to the cylindrical electrode of FIG. 9.
- the presently preferred method of making the sectional electrode of FIGS. 69 is to use a substrate with a plurality of conductors thereon, such as the substrate 31 with the conductors R1 R7.
- the low conductivity material is applied over the conductors in the uncured condition.
- Each section is then cured separately by applying a voltage source across the conductors which define the section. The applied voltage heats the section and the curing time and temperature is selected for each section to produce a cured material having the de sired conductivity.
- first and second substantially planar electrodes are first and second substantially planar electrodes
- each of said electrodes having an electrical insulating substrate with a low conductivity surface at said gap and means defining a plurality of spaced locations along the surface; means for connecting a first voltage source to said first electrode providing defined voltages between said spaced locations of said first electrode;
- electrostatic potentials substantially corresponding to the electrostatic potentials for concentric spherical metal electrodes so that the extensions of the 6 electric field lines in said gap converge substantially to a point.
- each of said electrodes includes a dielectric sheet substrate with a plurality of spaced conductors on the gap surface thereof for connection to the corresponding voltage source.
- each of said electrodes includes a dielectric sheet substrate with a plurality of spaced conductors on the gap surface thereof,
- each of said electrodes includes:
- each of said layers has a surface resistivity in the range of about 10 to 10 ohms per square.
- each of said means for connecting said first and second voltage sources includes a voltage divider with points along the divider connected to the conductors of the corresponding electrode.
- An imaging chamber as defined in claim 11 with said means for connecting said third voltage source providing said connection between corresponding conductors of said first and second electrodes.
- each of said first and second voltage sources provides an electrode current and said third voltage source provides a gap current, with the relative magnitudes of said sources such that the electrode current is substantially greater than the gap current.
- An imaging chamber as defined in claim 1 including a first resistance connected in parallel with said first electrode.
- An imaging chamber as defined in claim including a second resistance connected in parallel with said second electrode.
- each of said electrode low conductivity surfaces is formed of a plurality of side-by-side sections. with adjacent sections of different and substantially uniform conductivities, with the section conductivity decreasing from the center to the edge of the electrode.
- first and second substantially planar electrodes means for mounting said electrodes in the chamber in spaced relation defining a gap therebetween;
- each of said electrodes having an electrical insulating substrate with a low conductivity surface at said gap and a plurality of spaced conductors along said surface;
- electrostatic potentials substantially corresponding to the electrostatic potentials for concentric spherical metal electrodes so that the extensions of the electric field lines in said gap converge substantially to a point.
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Abstract
Description
Claims (24)
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
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US530057A US3922547A (en) | 1974-12-06 | 1974-12-06 | Virtual electrode imaging chamber |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
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US530057A US3922547A (en) | 1974-12-06 | 1974-12-06 | Virtual electrode imaging chamber |
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US3922547A true US3922547A (en) | 1975-11-25 |
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US530057A Expired - Lifetime US3922547A (en) | 1974-12-06 | 1974-12-06 | Virtual electrode imaging chamber |
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Cited By (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP0002295A2 (en) * | 1977-12-07 | 1979-06-13 | Agfa-Gevaert N.V. | Method of recording X-ray images and imaging chamber suited therefor |
US4249078A (en) * | 1978-05-05 | 1981-02-03 | Siemens Aktiengesellschaft | Arrangement for the production of electroradiographic x-ray photographs |
US5025376A (en) * | 1988-09-30 | 1991-06-18 | University Of Florida | Radiation teletherapy imaging system having plural ionization chambers |
Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3859529A (en) * | 1973-01-02 | 1975-01-07 | Xonics Inc | Ionography imaging chamber |
US3879610A (en) * | 1973-08-27 | 1975-04-22 | Diagnostic Instr Inc | Ionographic exposure method, apparatus |
US3883740A (en) * | 1973-08-14 | 1975-05-13 | Xonics Inc | Ionography imaging chamber for variable distance X-ray source |
-
1974
- 1974-12-06 US US530057A patent/US3922547A/en not_active Expired - Lifetime
Patent Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3859529A (en) * | 1973-01-02 | 1975-01-07 | Xonics Inc | Ionography imaging chamber |
US3883740A (en) * | 1973-08-14 | 1975-05-13 | Xonics Inc | Ionography imaging chamber for variable distance X-ray source |
US3879610A (en) * | 1973-08-27 | 1975-04-22 | Diagnostic Instr Inc | Ionographic exposure method, apparatus |
Cited By (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP0002295A2 (en) * | 1977-12-07 | 1979-06-13 | Agfa-Gevaert N.V. | Method of recording X-ray images and imaging chamber suited therefor |
EP0002295A3 (en) * | 1977-12-07 | 1979-06-27 | Agfa_Gevaert Naamloze Vennootschap | Method of recording x-ray images and imaging chamber suited therefor |
US4254033A (en) * | 1977-12-07 | 1981-03-03 | Agfa-Gevaert N.V. | Method of recording X-ray images and imaging chamber suited therefor |
US4249078A (en) * | 1978-05-05 | 1981-02-03 | Siemens Aktiengesellschaft | Arrangement for the production of electroradiographic x-ray photographs |
US5025376A (en) * | 1988-09-30 | 1991-06-18 | University Of Florida | Radiation teletherapy imaging system having plural ionization chambers |
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Legal Events
Date | Code | Title | Description |
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AS | Assignment |
Owner name: ELSCINT, INC., MASSACHUSETTS Free format text: ASSIGNORS DO HEREBY QUITCLAIM, ASSIGN AND TRANSFER THEIR ENTIRE RIGHTS, TITLE AND INTEREST THEY MAYHAVE IN SAID INVENTIN TO ASSIGNEES;ASSIGNORS:XONICS, INC.;XONICS MEDICAL SYSTEMS, INC.;REEL/FRAME:005029/0007 Effective date: 19880718 Owner name: ELSCINT IMAGING, INC., MASSACHUSETTS Free format text: ASSIGNORS DO HEREBY QUITCLAIM, ASSIGN AND TRANSFER THEIR ENTIRE RIGHTS, TITLE AND INTEREST THEY MAYHAVE IN SAID INVENTIN TO ASSIGNEES;ASSIGNORS:XONICS, INC.;XONICS MEDICAL SYSTEMS, INC.;REEL/FRAME:005029/0007 Effective date: 19880718 Owner name: ELSCINT, LIMITED, ILLINOIS Free format text: ASSIGNORS DO HEREBY QUITCLAIM, ASSIGN AND TRANSFER THEIR ENTIRE RIGHTS, TITLE AND INTEREST THEY MAYHAVE IN SAID INVENTIN TO ASSIGNEES;ASSIGNORS:XONICS, INC.;XONICS MEDICAL SYSTEMS, INC.;REEL/FRAME:005029/0007 Effective date: 19880718 |
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AS | Assignment |
Owner name: XONICS INC., A CA. CORP., ILLINOIS Free format text: RELEASED BY SECURED PARTY;ASSIGNOR:FIRST CHICAGO INVESTMENT CORPORATION, AS AGENT;REEL/FRAME:005013/0715 Effective date: 19881207 |