PSAPD gamma camera for SPECT imaging

Conventional scintillation cameras use scintillators coupled to arrays of photomultiplier tubes (PMTs) to produce simultaneous position and energy information for gamma-ray imaging. However, much effort has been devoted to the development of solid state detectors for scintillation cameras. while solid state detectors are more reliable than PMTs, previously investigated solid state detectors require pixellization to produce position resolution, which greatly increases the number of amplifier channels, and the cost, needed to configure a gamma-ray imaging system. New position sensitive avalanche photodiodes (PSAPDs) offer a potential solution since they can produce simultaneous position and energy resolution with a small number of amplifier channels. To demonstrate this we have used a 28 x 28 mm(2) PSAPD with a scintillator to image Tc-99m using only five amplifier channels. One face of a 7 x 7 array of CsI(TI) segments, each 3 x 3 x 4 mm(3), is coupled to a PSAPD with optical grease. A flood image, from a Tc-99m point source and no collimator, has a count-profile showing a peak-to-valley ratio of 7.5:1. Line images, from a 0.5 mm diameter capillary tube filled with Tc-99m solution and a parallel-hole collimator, have line response functions indicating that the spatial resolution is dominated by the scintillator segments having a width of 3 mm. These measurements indicate that an array of PSAPDs coupled to a segmented scintillator offers excellent performance for gamma-ray imaging.