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 × 128 active pixels of 30 × 50 µm 2 size and targets to overcome the PIXSIC probe drawbacks by exploiting a thin sensitive layer of 18 µm, still featuring an overall thickness close to 300 µm. 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 µm × 12000 µm was fabricated and tested in laboratory. The whole sensor dissipates 160 µW and its imaging capabilities were asserted with various sources : 55 Fe, 90 Sr and 18 F. 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 insensitivity to 511 keV γ-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.
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Radioisotope imaging is a powerful tool to understand the biological mechanisms in-vivo, especially in the brain of small animals, providing a significant model to study the human brain.
In this context, we have developed and built a pixelated intracerebral positron probe to be embedded on awake and freely moving small animals, typically rats. This pixelated probe will represent a key instrument for neuroscientists to study neural mechanisms and correlate them to behavioral experiments.
We describe in this paper the simulations carried out to design the intracerebral sensor, its architecture, and the detection of positrons in a volume with a couple of sensors assembled back-to-back. We also depict the architecture of the wireless acquisition system. Finally, we present the first measurements performed in real-time by this miniaturized probe with sealed radioactive sources and a 18F solution.
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