First results of a highly granulated 3D CdTe detector module for PET.

We present the performance of a highly granulated 3D detector module for PET, consisting of a stack of pixelated CdTe detectors. Each detector module has 2 cm  ×  2 cm  ×  2 cm of CdTe material, subdivided into 4000 voxels, where each voxel has size 1 mm  ×  1 mm  ×  2 mm and is connected to its own read-out electronics via a BiSn solder ball. Each read-out channel consists of a preamp, a discriminator, a shaper, a peak-and-hold circuit and a 10 bits SAR ADC. The preamp has variable gain where at the maximum gain the ADC resolution is equivalent to 0.7 keV. Each ASIC chip reads 100 CdTe pixel channels and has one TDC to measure the time stamp of the triggered events, with a time resolution of less than 1 ns. With the bias voltage set at  -250 V mm-1 and for 17838 working channels out of a total of 20 000, we have obtained an average energy resolution of 2.2% FWHM for 511 keV photons. For 511 keV photons that have undergone Compton scattering, we measured an energy resolution of 3.2% FWHM. A timing resolution for PET coincidence events of 60 ns FWHM was found.