Single-tube miniature gamma camera

In certain medical gamma imaging applications, conventional cameras are too large for practical use. To address these situations, we have constructed a clinically usable miniature gamma camera for photon energies up to 160 keV. The camera has outer dimensions of 92 mm x 92 mm x 190 mm and weighs 5 kg. Included in that mass is a collimator, an internal high-voltage power supply, and all shielding. The camera also has a position-sensitive photomultiplier tube (PSPMT) coupled to an 8-mm thick NaI(Tl) crystal; this crystal/tube combination provides signals to internal processing circuits. External electronics and analog-to-digital conversion circuits are connected to a Macintosh Quadra computer where additional processing, storage, and display of the signals takes place. Because the PSPMT has non-uniform energy response that results in geometric distortion if conventional position-arithmetic calculations are used, we have implemented a maximum-likelihood position-estimation calculation that produces undistorted images. The present version of the camera has a usable field of view of 48 mm x 48 mm and an intrinsic spatial resolution of 2.4 to 3.8 mm full width at half maximum.