Claims
- 1. A substrate material for use in a panel type radiation sensitive imaging intensifier tube having an evacuated tube envelope, an input window and an output window, said substrate material mountable in the tube envelope for supporting at least a conductive coating, and comprising a pattern etched glass plate defining an array of through holes partitioned by straight walls tapering to a sharp edge on the side of said material oriented toward the input window when mounted in the tube envelope, wherein the thickness of the substrate material is substantially greater than the hole width.
- 2. The substrate material of claim 1 wherein the through holes are hexagonal in shape.
- 3. The substrate material of claim 1 wherein the array of through holes form a honeycomb structure.
- 4. A substrate material for use in a radiation sensitive image intensifier tube having an evacuated tube envelope, an input window and an output window, said substrate material mountable in the tube envelope for supporting at least a conductive coating, and comprising a pattern etched glass plate defining an array of through holes partitioned by straight walls tapering to a sharp edge on the side of said material oriented toward the input window when mounted in the tube envelope, wherein the thickness of the substrate material is substantially greater than the hole width.
- 5. The substrate material of claim 4 wherein the through holes are hexagonal in shape.
- 6. The substrate material of claim 4 wherein the array of through holes form a honeycomb structure.
TECHNICAL FIELD
This application is a divisional of copending application Ser. No. 838,100 filed Mar. 10, 1986 entitled Improved Panel Type Radiation Image Intensifier which issued as Patent No. 4,730,107.
The present invention relates generally to the field of radiation imaging and, more particularly to an x-ray image intensifier tube of the proximity type for medical x-ray diagnostic use.
In U.S. Pat. No. 4,255,666 owned by the present assignee, a two-stage, proximity type image intensifier is described. This device incorporated two stages of amplification in an effort to provide improved gain over that of a single-stage device described in U.S. Pat. No. 4,140,900 also owned by the present assignee. Both U.S. Pat. Nos. 4,140,900 and 4,255,666 are hereby expressly incorporated herein by reference.
The two stage device described in U.S. Pat. No. 4,255,666 incorporates a flat scintillator screen, an output display screen and an amplification means intermediate to the scintillator screen and the output display screen. The two stage image intensifier tube comprises a metallic vacuum tube envelope and a metallic, inwardly concave input window.
In operation, an x-ray source generates a beam of x-rays which passes through a patient's body and casts a shadow onto the input window of the tube. The x-ray image passes through the input window and impinges upon the flat scintillation screen which is deposited on an aluminum substrate. The scintillation screen converts the x-ray image into a light image. This light image is "contact transferred" directly to an immediately adjacent first photocathode layer which converts the light image into a pattern of electrons. The scintillation screen and photocathode layer comprise a complete assembly.
A first phosphor display screen is mounted on one face of a fiber optic plate which is suspended from the tube envelope by means of insulators. On the opposite face of the fiber optic plate a second photocathode is deposited. The fiber optic plate is oriented in a plane substantially parallel to the plane of the scintillation screen.
A second phosphor display screen is deposited on an output window. A high voltage power supply is connected between the first phosphor display screen and the first photocathode as well as between the second photocathode and the second phosphor display screen. The power supply provides approximately 15 kV to each stage (approximately 30 kV total). The first display screen and the second photocathode are connected together and operate at the same potential.
In operation, the electron pattern on the negatively charged first photocathode layer is accelerated towards the first, positively charged (relative to the photocathode layer) phosphor display screen by means of the electrostatic potential supplied by the high voltage source connected between the display screen and the photocathode screen. The electrons striking the display screen produce a corresponding light image which passes through the fiber optic plate to impinge on the second photocathode. The second photocathode then emits a corresponding pattern of electrons which are accelerated toward the second phosphor display screen to produce an output light image which is viewable through the output window.
While the two-stage device described above did achieve fundamental performance improvements in gain as well as other parameters over the single-stage device, it still did not achieve the performance of conventional inverter type x-ray image intensifiers. Performance of the two-stage device is found to fall short in three distinct areas brightness gain, contrast ratio and limiting resolution.
The two-stage device has a conversion brightness of approximately one-third that of conventional inverter type tubes. This difference is due in part to the fact that the two-stage device is a unity magnification device while conventional inverter type tubes are typically X10 demagnification devices. This difference translates directly to a 100 fold increase in conversion gain. The image size of the inverter type tube is however only 1/10th that of the two-stage device.
The two-stage device did achieve a threefold increase in gain over the single-stage device by the incorporation of the fiber optic element. This element, however, added significantly to the cost of the device, increased its overall weight and reduced its ruggedness as well. Further increases in gain have not been achieved due to the prohibitive cost of providing additional stages of amplification or the inability to further optimize the efficiency of the various layers which comprise the twostage device.
Image contrast of the two-stage device has also been found inferior to the conventional inverter type tubes. Typically large area contrast ratios for the inverter tubes are better than 20:1 while the two-stage device exhibits a 15:1 contrast ratio. The loss of image contrast in the two-stage device is primarily due to reflected light and backscattered electrons within the space between the photocathode and phosphor layers. In inverter type tubes the same problems exist but to a lesser degree since the large space between the single photocathode and phosphor layers allow for a substantial amount of dispersion. Attempts to improve the performance of the two-stage device through the incorporation of anti-reflection layers and optimization of the aluminum layer coatings on the phosphor screens have rarely achieved the 20:1 contrast of the inverter type tubes.
Resolution is a measure of how faithfully an optical device reproduces detail. In this respect, the two-stage device suffers in performance by up to 30% due largely to the extreme sensitivity of its proximity focussing technique to the surface texture of the cesium iodide scintillator. This degradation is compounded by optical and x-ray scattering within the scintillator. Thinner scintillators or scintillators composed of finer crystals could offer improvements. However, thinner crystals reduce scintillator efficiency and gain while a finer crystal structure further roughens the surface.
It is therefore an object of this invention to overcome the above referenced problems and others by providing an improved panel type image intensifier tube whose performance is comparable to that of conventional inverter type tubes.
The disadvantages of the prior art as described above are reduced or eliminated by the provision of an improved panel type image intensifier tube.
The proximity type, radiation sensitive image intensifier tube of the present invention comprises an open ended, hollow, evacuated envelope which is closed on one end by a metallic, concave input window and at the opposite end by a glass output window. A first substrate material defining a plurality of cells or through holes is provided. The cells are preferably hexagonal in shape similar to a honeycomb structure. The walls of the cells are coated with a thin conductive, reflective layer preferably aluminum. A scintillator material, preferably cesium iodide, fills the voids of the cells. The scintillator material converts a pattern of impinging radiation into a corresponding light pattern. The light pattern is contact transferred to a first flat photocathode layer which lies substantially parallel and immediately adjacent the first substrate material. The first photocathode layer in turn, converts the light pattern into a corresponding first photoelectron pattern.
A second substrate material defining a plurality of cells or through holes is also provided. The walls of the cells are coated with a thin conductive layer preferably aluminum. The second substrate is spaced from the first photocathode layer on a side opposite the input window. A transparent support layer is mounted to the second substrate on an end opposite the first substrate material. A first flat phosphor display screen is mounted to the transparent support layer on a side internal to the second substrate material. The first photoelectron pattern emitted by the first photocathode is directed to the first display screen via the second substrate material. The photoelectrons striking the first display screen cause it to emit photons in a pattern corresponding to the first photoelectron pattern. A second, flat photocathode layer is mounted substantially parallel and immediately adjacent to the transparent support layer on a side opposite the first display screen. Photons emitted from the first display screen strike the second photocathode layer which converts the photons to a corresponding second photoelectron pattern.
A third substrate material defining a plurality of cells or through holes is also provided. The cells are again coated with a thin conductive layer preferably aluminum. The third substrate material is spaced from the second photocathode layer on a side opposite the first substrate material. A second flat phosphor display screen is mounted to the third substrate material and is substantially parallel to the second photocathode layer. The second photoelectron pattern emitted by the second photocathode layer is directed to the second display screen via the third substrate material. The photoelectrons striking the second display screen are converted to a visual image corresponding to the incident radiation pattern.
Means are also provided for applying separate electrostatic potentials between the first and second substrate materials and the second and third substrate materials respectively. The electrostatic potentials accelerate the first and second photoelectron patterns toward the first and second display screens respectively.
In the preferred embodiment the substrate material is pattern etched glass or glass-ceramic. The etching provides through holes or cells with straight angular walls. The walls taper to a sharp edge.
In an alternate embodiment of the present invention a proximity type, radiation sensitive image intensifier tube is provided. The tube is characterized by a scintillator stage which converts impinging radiation into a corresponding light pattern; a light amplification stage following the scintillation stage for producing a first pattern of photoelectrons corresponding to the first light pattern, accelerating the first pattern of photoelectrons along a path and converting the first pattern of photoelectrons to a second corresponding light pattern; and an output stage following the light amplification stage for producing a second pattern of photoelectrons corresponding to the second light pattern, accelerating the second photoelectron pattern along a path substantial in line with the path of the first photoelectron pattern and converting the second photoelectron pattern to a visible light image. At least one of the above described stages comprises a substrate material defining a plurality of cells. The cells are aligned along the path of the accelerated photoelectrons. The cell walls are coated with a thin conductive coating, preferably aluminum.
It is therefore an object of the present invention to provide an improved proximity type radiation image intensifier having improved gain, contrast ratio and resolution.
It is still another object of the present invention to provide an improved proximity type radiation image intensifier at a reduced cost.
It is still another object of the present invention to provide an improved proximity type radiation image intensifier with substantially less weight.
It is still another object of the present invention to provide an improved proximity type radiation image intensifier having improved resistance to environmental factors such as shock and vibration.
The foregoing and other objectives, features and advantages of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description of the preferred embodiment.
US Referenced Citations (19)
Foreign Referenced Citations (3)
| Number |
Date |
Country |
| 0126564 |
Nov 1984 |
EPX |
| 3325035 |
Jan 1985 |
DEX |
| 1444161 |
Jul 1976 |
GBX |
Non-Patent Literature Citations (1)
| Entry |
| Corning Product Brochure No. FPG-4 "Fotoform and Fotoceram" Precision Photosensitive Glass Materials (not dated). |
Divisions (1)
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Number |
Date |
Country |
| Parent |
838100 |
Mar 1986 |
|
Patent Grant
4855589
