First results from MADPET-II: a novel detector and readout system for high resolution small animal PET

MADPET-II is a novel, high-resolution 3D LSO-APD small animal PET scanner. The unique detector design and data acquisition system increase sensitivity while preserving spatial resolution, and open up new possibilities for data analysis. MADPET-II consists of a ring of dual layer detector modules (O 71 mm), each containing a 4×8 array of 2×2×6 mm³ (front) and 2×2×8 mm³ (back) LSO crystals that are each optically isolated and coupled one-to-one to a monolithic 4×8 APD array. Monte Carlo simulations have calculated system spatial resolution and point source sensitivity to be 1.1 mm FWHM and 2.8 %, respectively. Signals from each channel are individually processed using fully integrated 16-channel, low-noise, charge-sensitive preamplifiers and custom integrated electronics that include a 4 channel shaping amplifier, peak detector and nondelay line CFD. ADCs and TDCs digitise the pulse height and time-stamp each event, and data are stored exclusively in list mode format. Two 32 channel detector blocks were tested in coincidence and in a dual layer configuration. Data were processed and coincidences were sorted post-acquisition in software. Average energy resolution for a single detector block ranged from 14.3% FWHM to 16.9% FWHM. System pulse height linearity was measured, and all channels responded linearly with R² > 0.9988. Intrinsic uniformity for each detector block ranged from 2.0% to 4.8%. Overall system timing resolution ranged from 7.2 ns to 7.7 ns, with individual LORs having time resolutions as low as 2 ns.