Development of a Multi-Pixel Photon Counter Module for Positron Emission Tomography

A new detector module for positron emission tomography using multi-pixel photon counters (MPPCs) was developed. The detection area is 40 mm × 40 mm using an 8 × 8 MPPC array. The active area of each MPPC is 3 mm × 3 mm. The detector module contains preamplifiers, digital-to-analog converters for setting the bias offset, a 2D resistor network for position encoding, a high-voltage module, a temperature sensor, and embedded microprocessor units. Since the MPPC gain depends on temperature, compensation was performed by varying the bias voltage. Two kinds of flood images of an 8 × 8 array (5-mm pitch) and a 32 × 32 (1.25-mm pitch) array were acquired and examined. The timing resolution and the effect of dark counts were evaluated. With a reference detector consisting of a BaF₂ crystal coupled to a PMT, the timing resolution was 354 ps when a single 5 mm × 5 mm × 20 mm LYSO scintillator was coupled to one MPPC channel. However, the time resolution of the array deteriorated because of the increase in dark counts.