J. Trummer

A Time-Based Front End Readout System for PET & CT

In the framework of the European FP6s BioCare project, we develop a novel, time-based, photo-detector readout technique to increase sensitivity and timing precision for molecular imaging in PET and CT. The project aims to employ Avalanche Photo Diode (APD) arrays with state of the art, high speed, front end amplifiers and discrimination circuits developed for the Large Hadron Collider (LHC) physics program at CERN, suitable to detect and process photons in a combined one-unit PET/CT detection head. In the so-called time-based approach our efforts focus on the systems timing performance with sub-nanosecond time-jitter and -walk, and yet also provide information on photon energy without resorting to analog to digital conversion. The bandwidth of the electronic circuitry is compatible with the scintillators intrinsic light response (e.g. les40ns in LSO) and hence allows high rate CT operation in single-photon counting mode. Based on commercial LSO crystals and Hamamatsu S8550 APD arrays, we show the system performance in terms of timing- and energy resolution as well as its rate behavior (SPICE, simulating a high intensity X-ray beam). If proven viable, this technique may lead to the construction of a compact, radiation tolerant, and cost effective PET/CT detection head in one unit.

Scintillation properties of LuYAP and LYSO crystals measured with MiniACCOS, an automatic crystal quality control system

The Crystal Clear Collaboration has built a small animal PET, the ClearPETtrade and is now working on a dedicated PET for mammography, the ClearPEMtrade. The gamma-ray detectors in these machines consist of matrices of small scintillation crystals coupled to photo detectors. In all the detectors for the ClearPEMtrade about 6000 LYSO (2times2times20 mm3) crystals are used while for the ClearPETtrade the number is around 5000 LYSO and the same amount of LuYAP crystals with a dimension of 2times2times10 mm3 in a phoswich combination. An automatic system to measure the light yield, decay time and energy resolution of those L(Y)SO and Lu(Y)AP pixels of different sizes on a fast basis (around 500 per day) was constructed at CERN, the MiniACCOS (mini automatic crystal quality control system). This paper offers a short description of the MiniACCOS system and presents first results of crystal measurements of about 10000 LYSO and LuYAP pixels and compares them to previously produced batches of LuYAP crystals produced by two different growth methods