Radiant energy – Invisible radiant energy responsive electric signalling – Semiconductor system
Reexamination Certificate
1998-04-16
2001-01-30
Ham, Seungsook (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
Semiconductor system
C250S390110
Reexamination Certificate
active
06180946
ABSTRACT:
TECHNICAL FIELD
The present invention relates to energetic particle imaging and, more specifically, to radiation imaging cameras.
BACKGROUND ART
There are various types of radiation imaging cameras available including gamma ray cameras and neutron cameras. Two types of imaging gamma detectors are in wide use. Gamma cameras used for nuclear medicine are descendants of the Anger camera and consist of a scintillating crystal viewed by an array of photo multipliers (PMTs). See Anger H O. “Scintillation Camera,”
Rev Sci. Instr
. 1958; 29: 27, which is hereby incorporated by reference herein. When an incident energetic penetrating particle is absorbed by a crystal, it produces a scintillation event. The total measured scintillation is used to determine the radiation energy. Its position is determined by centroiding the location on the array of PMTs. The intrinsic spatial resolution is limited by the size of the PMTs and the Poisson statistics of the scintillation. These detectors typically have intrinsic resolution of several mm with arrays of 50-100 PMTs.
A second type of gamma detector consists of an array of photosensitive crystals such as ZnCdTe. These detectors have better energy resolution than the Anger camera since their photo detection efficiency is much greater than the product of the scintillation efficiency and the subsequent PMT quantum efficiency. However, it is currently very expensive to fabricate an array with many pixels. These detectors have found application in coded aperture gamma-ray astronomy detectors with up to thousands of discrete pixels.
Another type of ionizing radiation camera is designed to locate neutrons. Two-dimensional position sensitive neutron detectors are currently limited in either their spatial or temporal resolution. Scintillator-based detectors similar to the Anger camera have only modest spatial resolution as do He
3
thermal neutron detectors. As compared to the scintillator and He
3
detectors, CCD-based detectors have good spatial resolution, however they are not counting detectors and therefore have poor temporal resolution. Additionally, CCD-based detectors lack the ability to discriminate gamma rays from neutrons. This limits neutron imaging of special nuclear material and use of neutron scattering for diagnostic purposes and nondestructive testing.
SUMMARY OF THE INVENTION
The present invention introduces a new class of imaging radiation detectors. In a preferred embodiment, an ionizing radiation camera uses a scintillator to convert invisible radiation to visible radiation and photo multipliers(PMTs) to determine the energy of the radiation. The scintillation is spatially resolved by imaging it onto a photon counting and position sensitive detector, which may be implemented with a precision analog photon address (PAPA) detector. In one embodiment of the invention, the PAPA detector determines the scintillation position on a 1024×1024 pixel grid in ~100 ns.
In an embodiment, the ionizing radiation camera comprises a scintillator for emitting photons in response to radiation incident upon the scintillator, and a photon counting and position sensitive detector in optical communication with the scintillator for providing the position of the radiation. The scintillator emits a first group of photons, indicative of the position of the radiation, along a first path in the direction of the photon counting and position sensitive detector, so that the photon counting and position sensitive detector is responsive to this first group of photons and provides position information of the radiation. The scintillator emits a second group of photons in response to the radiation along a second path. One or more photo detectors are responsive to this second group of photons so as to determine a characteristic of the radiation, such as the type of radiation or the energy level.
In another embodiment, an optical lens is positioned to receive emitted photons from the scintillator for directing the emitted photons onto the photon counting and position sensitive detector.
In yet another embodiment of the invention, the scintillator, has an internally mirrored front radiation entrance and a side for allowing some of the emitted photons to exit.
In a further embodiment of the invention, the scintillator, is square and has an internally mirrored radiation entrance and a clear exit window. Two of the four sides are mirrored while the other two sides are clear and allow some of the emitted photons to exit.
In yet another embodiment, the photon counting and position sensitive detector is a PAPA detector. An optional imaging plate may be positioned such that the radiation is guided through n aperture in the imaging plate and directed toward the scintillator.
REFERENCES:
patent: 5783829 (1998-07-01), Sealock et al.
C. Papaliolios et al, “Speckle Imaging with PAPA Detector”, App. Opt. 24, 285 p. 287, Jan. 1985.
Anger, Hal. O., “Scintillation Camera”, Donner Laboratory of Bioophysics and Medical Physics and Radiation Laboratory, University of California, Berkeley, California, The Review of Scientific Instruments, vol. 29, No. 1, Jan. 1958, pp. 27-33.
Bromberg & Sunstein LLP
Ham Seungsook
Hanig Richard
Lexitek, Inc.
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