Implantable CMOS pixel sensor for positron imaging in rat brain

摘要

IMIC is a Monolithic Active Pixel Sensor prototype designed for the MAPSSIC project, which aims at developing wireless intracerebral probes dedicated to image positron-emitting source activity in the brain of awake and freely moving rats. Former experiments with the PIXSIC positron probe based on a passive sensor have validated the proof of concept, but have also shown limitations with regards to the probe robustness and to its transparency to annihilation photons. The IMIC circuit features a matrix of 16 x 128 active pixels of 30 x 50 mu m(2) size and targets to overcome the PIXSIC probe drawbacks by exploiting a thin sensitive layer of 18 mu m, still featuring an overall thickness close to 300 mu m. Additionally, by using a low power (55 nW/pixel) in-pixel front-end architecture providing binary output, IMIC solves the challenge of implanting an active sensor in tissues where overheating is forbidden.The needle-shaped sensor 610 mu m x 12000 mu m was fabricated and tested in laboratory. The whole sensor dissipates 160 mu W and its imaging capabilities were asserted with various sources: Fe-55, Sr-90 and F-18. These tests also demonstrated robust count-rate measurement with IMIC in the range 10-1000 counts/matrix/s. Finally, a dedicated setup qualitatively confirmed excellent in-sensitivity to 511 keV gamma-rays.In this paper, we present the sensor requirements and its detailed design. We also discuss the first characterisation results and the outlook for the integration of IMIC into an implantable probe.