Performance analysis of phoswich/APD detectors and low-noise CMOS preamplifiers for high-resolution PET systems

An integrated 0.8-mu CMOS charge-sensitive preamplifier previously designed for LSO/APD-based positron emission tomography (PET) systems has been furt her investigated for use with multicrystal/avalanche photodiode (APD) PET d etectors. In addition to low-noise wide-band performance and power efficien cy, high dynamic range and good signal-to-noise ratio over a broad range of shaping times are required to process the signals from crystals being used in phoswich detectors, which have a wide range of scintillation decay time and light output characteristics. The preamplifier equivalent noise charge (N-eq) was measured as a function of input capacitance and amplifier-shapi ng time constant. The performance of the preamplifier was also assessed usi ng APDs coupled to a variety of scintillators. Measurements were obtained a t a preamplifier input-device current of 2 and 4 mA. The higher bias led to marginal improvements of the timing performance but had no effect on energ y resolution. The very low noise of the preamplifier allows optimum timing performance to be obtained at lower APD gain and improves crystal identific ation by pulse shape discrimination with phoswich detectors.