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MAPSSIC, a Novel CMOS Intracerebral Positrons Probe for Deep Brain Imaging in Awake and Freely Moving Rats: A Monte Carlo Study

Abstract : Preclinical behavior neuroimaging gathers simultaneous assessment of behavior and functional brain imaging. It is a potential key breakthrough to improve the understanding of brain processes and assess the validity of preclinical studies in drug development. Achieving such a combination is difficult, anesthesia or restraints inherent to conventional nuclear imaging preclude its use for behavior studies. In that context, we have proposed an original strategy using submillimetric probes to directly measures positrons inside the rat brain. This paper gives the results of Monte Carlo simulations of a new generation of intracerebral positron probe based on a CMOS Monolithic Active Pixel Sensor. We present the results obtained for a probe into a large homogeneous volume of radioactive water (18 F) leading to a sensitivity of 0.88 cps · Bq −1 · mm 3 and a mean energy deposition by positrons of 15.1 keV. Simulation in simplified brain-shaped sources modeling a 11 C-raclopride experiment shows that the implanted volume modeling the left putamen contribute to 92.4 % of the signal from positrons. We also investigate the effects of the thickness of the sensitive layer, the energy threshold and pixel dimensions on the detection capacities of the sensor. We demonstrate that an increase in the sensitive thickness from 18 to 190 µm would lead to an increase of positrons sensitivity by a factor of 1.74, but to a decrease of the direct (positrons) to indirect (γ-rays and electrons) sensitivity ratio by a factor of 1.59. Finally we show that for a threshold lower than about 5 keV the effect of the pixel dimensions is negligible.
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L. Ammour, J. Heymes, M. Bautista, S. Fieux, F. Gensolen, et al.. MAPSSIC, a Novel CMOS Intracerebral Positrons Probe for Deep Brain Imaging in Awake and Freely Moving Rats: A Monte Carlo Study. IEEE Transactions on Radiation and Plasma Medical Sciences, IEEE, 2019, 3 (3), pp.302-314. ⟨10.1109/TRPMS.2018.2881301⟩. ⟨hal-02165345⟩

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