Development of two-dimensional position sensitive CdTe detector for next generation PET scanners

Objectives We have developed a two-dimensional position-sensitive CdTe detector for high resolution PET scanners. The detector provides high spatial resolution and good sensitivity. We report the position resolutions of the detector.

Methods The detector is composed of a 16-strip type CdTe detector (19.1×20×1t mm³) and two resistive chains for position readout. The strip type detector is characterized by an anode plane which has a resistive layer consisting of parallel strips (1.1mm wide, 1.2mm pitch). The first coordinate of interaction point is determined by the signals from strips. To reduce the number of electronic channels, the charge division method is employed: both ends of all strips are connected to resistive chains. The ratio of the signals obtained from both sides of the resistive chain determines the hit strips. To determine the coordinate along the strips, again charge division method is applied. We tested the detector (with 8 of 16 strips) with a collimated ²⁴¹Am source.

Results Excellent accuracies of 90% are confirmed in the central strips. Accuracies of 79.5% (for a side strip), 87.6%, 89.6%, 89.2%, 89.0%, 87.1%, 85.7% and 79.9% (for other side strip) were obtained. For second coordinate, resolutions of 0.8 – 1.4 mm FWHM were obtained. This includes the beam size of ~ 0.4 mm FWHM and therefore position resolutions of ~ 1 mm FWHM was achieved.

Conclusions High resolution of the detector, indicating feasibility of a high resolution three-dimensional (transaxial, axial and DOI) detector block was confirmed. Furthermore, due to the reduction in the number of electronics channels, a high packing ratio which is essential for a good sensitivity is achieved and therefore stacking pitch between detectors can be more reduced.