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 further investigated for use with multicrystal/avalanche photodiode (APD) PET detectors. In addition to low-noise wide-band performance and power efficiency, 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-shaping time constant. The performance of the preamplifier was also assessed using APDs coupled to a variety of scintillators. Measurements were obtained at 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 energy resolution. The very low noise of the preamplifier allows optimum timing performance to be obtained at lower APD gain and improves crystal identification by pulse shape discrimination with phoswich detectors.