Patent Number: 
Section: claims

1. A pinhole collimator assembly comprising a plurality of pinhole apertures therein, wherein each pinhole aperture has an adjustable aperture size and wherein the pinhole collimator assembly is configured so that gamma rays emitted by a subject being imaged pass through the plurality of pinhole apertures in the pinhole collimator assembly, but the remainder of the pinhole collimator assembly is substantially gamma ray absorbent. 2. The pinhole collimator assembly of claim 1, wherein the pinhole collimator assembly comprises an inner collimator comprising one or more inner pinhole apertures therein and an outer collimator comprising one or more outer pinhole apertures therein, wherein the inner collimator and the outer collimator are arranged so that the one or more inner pinhole apertures and the one or more outer pinhole apertures align to define the one or more pinhole apertures in the pinhole collimator assembly. 3. The pinhole collimator assembly of claim 2, wherein the pinhole collimator assembly is configured so that movement of at least one of the inner collimator or the outer collimator adjusts the aperture size of each of the one or more pinhole apertures in the pinhole collimator assembly. 4. The pinhole collimator assembly of claim 3, wherein the pinhole collimator assembly is configured so that the one or more pinhole apertures maintain a square shape while the aperture size is adjusted. 5. The pinhole collimator assembly of claim 2:wherein the one or more outer pinhole apertures open to an outer surface of the outer collimator; andwherein the one or more inner pinhole apertures open to an inner surface of the inner collimator. 6. The pinhole collimator assembly of claim 2, wherein the inner collimator and the outer collimator are generally cylindrically shaped, and wherein the pinhole collimator assembly is configured so that rotation and/or translation of at least one of the inner collimator or the outer collimator adjusts the aperture sizes of each of the one or more pinhole apertures in the pinhole collimator assembly. 7. The pinhole collimator assembly of claim 2, wherein the inner collimator and the outer collimator are generally non-cylindrically shaped, and wherein the pinhole collimator assembly is configured so that axial translation of at least one of the inner collimator or the outer collimator adjusts the aperture sizes of each of the one or more pinhole apertures in the pinhole collimator assembly. 8. The pinhole collimator assembly of claim 7, wherein the pinhole collimator assembly is configured so that the one or more pinhole apertures maintain a square shape while the aperture size is adjusted. 9. The pinhole collimator assembly of claim 2, wherein the inner collimator comprises a cylindrical body having the one or more inner pinhole apertures therein, and wherein the outer collimator comprises a cylindrical body having the one or more outer pinhole apertures therein, and wherein either the inner or outer collimator has an alignment pin extending radially from the cylindrical body and correspondingly either the outer or inner collimator has an alignment slot sized to receive the alignment pin. 10. The pinhole collimator assembly of claim 1, wherein the pinhole collimator assembly comprises a diaphragm, wherein the diaphragm comprises a plurality of blocks arranged to define a respective pinhole aperture, wherein the diaphragm is configured so that positioning the blocks with respect to one another adjust an aperture size of the respective pinhole aperture. 11. The pinhole collimator assembly of claim 10, wherein the plurality of blocks comprises four blocks that are arranged so that the respective pinhole aperture is four sided. 12. The pinhole collimator assembly of claim 10, wherein the plurality of blocks comprises a first pair of parallel blocks and a second pair of parallel blocks, wherein each pair of the parallel blocks are spaced a distance apart, and wherein the first pair of parallel blocks are generally perpendicular to the second pair of parallel blocks. 13. The pinhole collimator assembly of claim 12, wherein each of the first pair of parallel blocks is slidably interlocked with each of the second pair of parallel blocks. 14. The pinhole collimator assembly of claim 12, wherein each of the first pair of blocks are configured to move in a generally opposite direction with respect to one another, and wherein each of the second pair of blocks are configured to move in a generally opposite direction with respect to one another. 15. The pinhole collimator assembly of claim 12, wherein the diaphragm comprises a plate coupled to the plurality of blocks, wherein the plate comprises a central opening aligned with the respective pinhole aperture defined by the plurality of blocks and a plurality of slots, wherein each of the blocks comprises a body and one or more pins extending from the body and through a corresponding one of the slots in the plate. 16. The pinhole collimator assembly of claim 15, wherein the diaphragm comprises a ring coupled to the plate, wherein the ring comprises a central opening aligned with the respective pinhole aperture defined by the plurality of blocks and a plurality of slots in the ring, wherein each of the blocks comprises a body and one or more pins extending from the body and through a corresponding one of the slots in the ring. 17. The pinhole collimator assembly of claim 16, wherein the pinhole collimator assembly is configured so that rotation of the ring positions the blocks with respect to one another so as to adjust the aperture size of the respective pinhole aperture defined by the diaphragm. 18. The pinhole collimator assembly of claim 1:wherein the pinhole collimator assembly comprises a plurality of diaphragms arranged in a generally circular configuration;wherein each diaphragm comprises a plurality of blocks that defines a pinhole aperture in the pinhole collimator assembly; andwherein each diaphragm is configured so that positioning the blocks with respect to one another adjusts the size of the pinhole aperture. 19. An imaging system comprising:a pinhole collimator assembly comprising a plurality of pinhole apertures therein, wherein each pinhole aperture has an adjustable aperture size; anda detector assembly configured to generate one or more signals in response to gamma rays emitted by a subject being imaged that pass through the one or more apertures in the pinhole collimator assembly. 20. The imaging system of claim 19, wherein the imaging system comprises a single photon emission computed tomography system or a combined single photon emission computed tomography system/x-ray computed tomography system. 21. The imaging system of claim 19, wherein the detector assembly comprises at least one of an array of solid-state detector elements or a scintillator assembly coupled to light sensors. 22. The imaging system of claim 19, comprising:a module configured to receive the one or more signals and to process the one or more signals to generate one or more images; andan image display workstation configured to display the one or more images. 23. The imaging system of claim 19:wherein the pinhole collimator assembly comprises an inner collimator comprising one or more inner pinhole apertures therein and an outer collimator comprising one or more outer pinhole apertures therein;wherein the inner collimator and the outer collimator are arranged so that the one or more inner pinhole apertures and the one or more outer pinhole apertures align to define the one or more pinhole apertures in the pinhole collimator assembly; andwherein the collimator is configured so that movement of at least one of the inner collimator or the outer collimator adjusts the aperture size of one or more pinhole apertures in the pinhole collimator assembly. 24. The imaging system of claim 19, wherein the pinhole collimator assembly comprises a diaphragm, wherein the diaphragm comprises a plurality of blocks arranged to define a respective pinhole aperture in the pinhole collimator assembly, wherein the diaphragm is configured so that positioning the blocks with respect to one another adjust an aperture size of the respective pinhole aperture. 25. The imaging system of claim 19:wherein the pinhole collimator assembly comprises a plurality of diaphragms arranged in a generally circular configuration;wherein each diaphragm comprises a plurality of blocks that defines a pinhole aperture in the pinhole collimator assembly;wherein each diaphragm is configured so that positioning the blocks with respect to one another adjusts the size of the pinhole aperture. 26. A method of adjusting collimator performance comprising:adjusting aperture sizes of a plurality of apertures in a pinhole collimator assembly;collimating gamma rays emitted by a subject being imaged with the pinhole collimator assembly; anddetecting the collimated gamma rays. 27. The method of claim 26:wherein the pinhole collimator assembly comprises an inner collimator comprising one or more inner pinhole apertures therein and an outer collimator comprising one or more outer pinhole apertures therein; andwherein the inner collimator and the outer collimator are arranged so that the one or more inner pinhole apertures and the one or more outer pinhole apertures align to define the one or more pinhole apertures in the pinhole collimator assemblywherein adjusting the aperture size of the one or more pinhole apertures comprises moving at least one of the inner collimator or the outer collimator. 28. The method of claim 26, wherein each of the one or more pinhole apertures is defined by a diaphragm comprising a plurality of blocks arranged to define an aperture, and wherein adjusting the aperture size of the one or more pinhole apertures comprises moving the blocks of each diaphragm with respect to one another. 29. The method of claim 26, wherein each of the one or more pinhole apertures is defined by a diaphragm comprising a first pair of parallel blocks and a second pair of parallel blocks arranged, and wherein adjusting the aperture size of the one or more pinhole apertures comprises moving the first pair of parallel blocks in an opposite direction with respect to one another and moving the second pair of parallel blocks in an opposite direction with respect to one another.