A compact 64-pixel CsI(Tl)/Si PIN photodiode imaging module with IC readout

We characterize the performance of a complete 64-pixel compact gamma camera imaging module consisting of optically isolated 3 × 3 × 5 mm³ CsI(Tl) crystals coupled to a custom array of low-noise Si PIN photodiodes read out by a custom IC. At 50-V bias, the custom 64-pixel photodiode arrays demonstrate an average leakage current of 28 pA per 3 × 3 mm³ pixel, a 98.5% yield of pixels with <100 pA leakage, and a quantum efficiency of about 80% for 540-nm CsI(Tl) scintillation photons. The custom 64-channel readout IC uses low-noise preamplifiers, shaper amplifiers, and a winner-take-all (WTA) multiplexer. The IC demonstrates maximum gain of 120 mV/1000 e^-, the ability to select the largest input signal in less than 150 ns, and low electronic noise at 8-μs peaking time ranging from 25 e^- rms (unloaded) to an estimated 180 e^- rms (photodiode load of 3 pF, 50 pA). At room temperature, a complete 64-pixel detector module employing a custom photodiode array and readout IC demonstrates an average energy resolution of 23.4% FWHM and an intrinsic spatial resolution of 3.3-mm FWHM for the 140-keV emissions of ^99mTc. The construction of an array of such imaging modules is straightforward; hence this technology shows strong potential for numerous compact gamma camera applications, including scintimammography