Photodetector scintillator radiation imager having high efficiency light collection

#This invention relates generally to radiation imaging systems and more particularly to scintillator designs to improve light collection efficiency.

#Radiation imaging systems are widely used for medical and industrial purposes. For example, in nuclear medicine, certain diagnostic tests involve injection into the patient of radionuclides which will concentrate in an organ of interest. Radiation emitted from these radionuclides can be used for examining the organ's structure and its operation. External radiation sources, such as x-ray machines, are also be used for diagnostic purposes. Imaging systems have been developed which used the detected radiation to produce a signal which can be used to operate a visual display, such as a cathode ray tube or liquid crystal display device, or which can be used for other analyses of the pattern of detected x-ray or gamma radiation. In such systems the radiation is typically absorbed in a scintillator material, resulting in generation of photons of light. Light photons emanating from the scintillator are detected by photodetectors to generate an electrical output signal that can be processed to drive the display or analysis system.

#Particularly for radiation imagers employed in nuclear medicine procedures, in which it is desired to map the emitted radiation of a very low energy radionuclide taken up in the tissue of the patient, it is important that the imaging device be sensitive to low radiation levels while still being able to discriminate against background radiation. Efficient collection of the light photons generated when the incident radiation is absorbed in the scintillator allows detection of radiation with lower energy levels and thus enhances the diagnostic value of the imaging device.

#The features of the invention believed to be novel are set forth with particularity in the appended claims. The invention itself, however, both as to organization and method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in conjunction with the accompanying drawings in which like characters represent like parts throughout the drawings, and in which:

#FIG. 1 is a partial cross-sectional view of a device constructed in accordance with one embodiment of the present invention.

#FIG. 2 is a plan view of a portion of a scintillator array constructed in accordance with the embodiment of the present invention shown in FIG. 1.

#In FIG. 1, a radiation imaging device 10 comprises a photodetector array 20 disposed on a substrate 15, a scintillator array 30 comprising a plurality of scintillator elements 32 disposed over the photodetector array, a dielectric layer 40 extending around scintillator elements 32, and an optically reflective layer 50 disposed around the dielectric layer. Photodetector array 20 is coupled to a processing circuit 80, which processes electrical signals generated by the imager array for use in display and analysis equipment 90.

#Photodetector or imager array 20 comprises a plurality of photodetectors 22 arranged and electrically connected in a pattern, typically rows and columns. The photodetectors are disposed on imager substrate 15 to form an array that can be of any size and shape appropriate for the use of the imaging device 10, such as for medical analyses of particular portions of the body. The photodetectors are advantageously photodiodes, and alternatively may comprise other known solid state photodetector devices. Substrate 15 preferably comprises glass or ceramic material. A cable 24 carries the electrical signals generated in the photodetector to processing circuit 80.

#Scintillator 30 is positioned adjacent to, and is optically coupled to, photodetector array 20. As used herein, "optically coupled to photodetector array 20" refers to arranging the two arrays so that light photons from the scintillator readily pass into photodetectors; the optical coupling may include a separate optical coupling layer 25, as shown in FIG. 3, disposed between the scintillator element and the photodetector and which enhances efficient transfer of the light photons from the scintillator to the photodetectors. As illustrated in FIG. 1, scintillator 30 comprises a plurality of separate scintillator elements 32 which can be diced, or cut, from a larger block of scintillator material or which can be separately grown or deposited in columnar structures using a known method such as vapor deposition or sputtering. Each scintillator element comprises a first end surface 34 through which incident x-ray or gamma radiation 70 enters the scintillator elements, and a second end surface 36, which is opposite the first end surface, through which the light photons pass to the adjoining photodetector array 20. Each scintillator element 32 further comprises sidewalls 38 which extend between the respective first end and second end surfaces of the scintillator elements. Cesium iodide is the material that is typically used to form scintillator 30, but the scintillator can alternatively comprise other known scintillating materials.