Small form-factor, liquid-cooled SiPM module for PET/MRI applications

We present recent advances in the technology for small form factor hybrid circuits with one water cooled LTCC substrate, Silicon Photomultipliers (SiPMs) and highest-performance ASICs for application in scintillator detectors for time-of-flight (TOF) Positron Emission Tomography / Magnetic Resonance Imaging applications. One of the biggest challenges is the development of miniaturized sensor modules that are highly functional and MRI compatible. The SiPM modules with an area of 32.8 by 32.0 mm
²
contain 12 × 12 SiPMs in a pitch of 2.5 mm
²
. The readout of the 144 channels is performed by four PETA6 ASICs. The LTCC substrate with 2.1 mm thickness has been manufactured using the most advanced technologies developed at MSE. The liquid cooling channels inside the LTCC substrate provide excellent cooling for the ASICs, the SiPMs, and thermal insulation between ASICs and SiPMs and allow a very compact design of the detector modules, reducing their height by 50% compared with other technical solutions. The 12 SiPM arrays with 2×6 geometry are wire bonded only at the edges of the SiPMs to the LTCC, enabling the use of nearly the whole detector area for photon detection. At the opposite side of the substrate, four ASICs for the readout electronic with 272 μm bump pitch are flip-chip solder assembled to the LTCC substrate and underfilled and a few SMD components are mounted. LTCC substrates and all components are fully MRI compatible, which allows integration of PET with magnetic resonance imaging without mutual interference. A scintillator crystal array on top of the SiPMs converts gamma-rays produced by the decay of positrons into light. With measurements on prototypes the best coincidence resolving times (CRTs) for pairs of identical detectors in combination with high spatial resolution have been obtained.