Computer tomography apparatus using image intensifier detector
First Claim
1. A radiation therapy X-ray simulator having an X-ray source providing a fan beam, a gantry to support the X-ray source, a couch to support a patient and an image forming system including a computer for fan beam reconstruction without reordering, wherein the simulator is constructed such that the X-ray source is positioned relative to the couch in a geometry essentially identical to the geometry of the same elements of a target radiotherapy machine,the improvement comprising:
- said image forming system includes a first X-ray detector being an image intensifier (IIT) for converting X-rays from said source to electrons after said X-rays have passed through a patient, and for accelerating said electrons to an output phosphor screen to provide visible light, said first X-ray detector having a first quantum efficiency;
a photo diode linear array detector, said photo diode linear array detector replacing a TV camera, a plurality of photo diodes in said photo diode linear array detector having a second quantum efficiency of approximately 0.6 or more electrons per photon and a dynamic range on the order of 35,000 to 1, said photo diode linear array detector providing an electrical signal the amplitude of which is responsive to the intensity of said visible light;
a lens means, said lens means being interposed between said output phosphor screen and said photo diode detector for coupling visible radiation from said image intensifier to said photo diode detector, said lens means having a third quantum efficiency;
wherein an X-ray beam from said X-ray source becomes reduced in intensity as it passes through a portion of a patient and impinges upon said X-ray detector of said IIT at a first point and causes the emission of a visible light ray having an intensity which corresponds to the intensity of the impinging ray and spatially corresponds to said first point, and where said visible light ray passes through said lens means and intersects said photo diode detector at a second point, which second point spatial position and intensity correspond to the spatial position and intensity of said first point; and
wherein the product of said first, second and third quantum efficiencies is greater than unity.
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Accused Products
Abstract
Disclosed is a low cost computer tomographic (CT) scanner system specifically designed for radiation therapy treatment planning. A 512-channel photo-diode array with digitizing electronics converts image intensifier optical projection data directly into digital signals and has a dynamic range on the order of 100,000:1. The new simulator includes a rotating gantry, an X-ray generator with radiographic and fluoroscopic modes and a therapy style patient support assembly. Results on head and body size phantoms indicate that the simulator X-ray generator and image intensifier tube (IIT) with multi-channel photo-detector can produce photon statistic limited CT images. Software and hardware compensation methods are described which minimize geometrical distortions. Low noise, high input impedance electronics are employed which are phase-locked to the line frequency. A dual sample interval method is employed which effectively increases the range of the digital signal produced by the front-end electronics by three additional bits.
163 Citations
14 Claims
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1. A radiation therapy X-ray simulator having an X-ray source providing a fan beam, a gantry to support the X-ray source, a couch to support a patient and an image forming system including a computer for fan beam reconstruction without reordering, wherein the simulator is constructed such that the X-ray source is positioned relative to the couch in a geometry essentially identical to the geometry of the same elements of a target radiotherapy machine,
the improvement comprising: -
said image forming system includes a first X-ray detector being an image intensifier (IIT) for converting X-rays from said source to electrons after said X-rays have passed through a patient, and for accelerating said electrons to an output phosphor screen to provide visible light, said first X-ray detector having a first quantum efficiency; a photo diode linear array detector, said photo diode linear array detector replacing a TV camera, a plurality of photo diodes in said photo diode linear array detector having a second quantum efficiency of approximately 0.6 or more electrons per photon and a dynamic range on the order of 35,000 to 1, said photo diode linear array detector providing an electrical signal the amplitude of which is responsive to the intensity of said visible light; a lens means, said lens means being interposed between said output phosphor screen and said photo diode detector for coupling visible radiation from said image intensifier to said photo diode detector, said lens means having a third quantum efficiency; wherein an X-ray beam from said X-ray source becomes reduced in intensity as it passes through a portion of a patient and impinges upon said X-ray detector of said IIT at a first point and causes the emission of a visible light ray having an intensity which corresponds to the intensity of the impinging ray and spatially corresponds to said first point, and where said visible light ray passes through said lens means and intersects said photo diode detector at a second point, which second point spatial position and intensity correspond to the spatial position and intensity of said first point; and wherein the product of said first, second and third quantum efficiencies is greater than unity. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
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Specification