New concept of a submillimetric pixellated Silicon detector for intracerebral application M. Benoit a , J. M¨ ark b , P. Weiss b , D. Benoit c , J.C. Clemens b , D. Fougeron b , B. Janvier c , M. Jevaud b , S. Karkar b , M. Menouni b , F. Pain c , L. Pinot c , C. Morel b , P. Laniece c,n a Laboratoire de l’Acce´le ´rateur Line´aire (LAL, Universite´ Paris Sud, CNRS/IN2P3, UMR 8608), Orsay, France b Centre de Physique des Particules de Marseille (CPPM, Universite´ Aix-Marseille, CNRS/IN2P3, UMR 6550), Marseille, France c Imagerie et Mode ´lisation en Neurobiologie et Cance ´rologie (IMNC, Universite´ Paris Sud et Paris Diderot, CNRS/IN2P3, IMNC, Centre Universitaire, batiment 440, 91406 Orsay Cedex, UMR 8165), Orsay, France article info Article history: Received 15 April 2011 Received in revised form 6 July 2011 Accepted 9 August 2011 Keywords: Intracerebral probe PET imaging Silicon pixel detectors Small animal imaging abstract A new beta þ radiosensitive microprobe implantable in rodent brain dedicated to in vivo and autonomous measurements of local time activity curves of beta radiotracers in a volume of brain tissue of a few mm 3 has been developed recently. This project expands the concept of the previously designed beta microprobe, which has been validated extensively in neurobiological experiments performed on anesthetized animals. Due to its limitations considering recordings on awake and freely moving animals, we have proposed to develop a wireless setup that can be worn by an animal without constraining its movements. To that aim, we have chosen a highly beta sensitive Silicon-based detector to devise a compact pixellated probe. Miniaturized wireless electronics is used to read-out and transfer the measurement data. Initial Monte-Carlo simulations showed that high resistive Silicon pixels are appropriate for this purpose, with their dimensions to be adapted to our specific signals. More precisely, we demonstrated that 200 mm thick pixels with an area of 200 mm  500 mm are optimized in terms of beta þ sensitivity versus relative transparency to the gamma background. Based on this theoretical study, we now present the development of the novel sensor, including the system simulations with technology computer-assisted design (TCAD) to investigate specific configurations of guard rings and their potential to increase the electrical isolation and stabilization of the pixel, as well as the corresponding physical tests to validate the particular geometries of this new sensor. & 2011 Elsevier B.V. All rights reserved. 1. Introduction The understanding of brain disorders, the neural processes involved in cognitive functions and their alterations in neurode- generative pathologies as well as testing new therapies for these diseases benefits greatly from the combined use of rodent models with the neuroimaging methods specifically adapted for the rodent brain. Besides magnetic resonance imaging (MRI) and functional MRI, positron-emission tomography (PET) remains a unique modality to study in vivo brain processes [1]. However, current high spatial resolution tomographs suffer from several limitations when applied to neuroscience such as low sensitivity and the need of restraining the animal during image acquisi- tion [2]. To overcome some of these limits, recent approaches have been proposed derived from preceding PET technologies including a miniature portable PET scanner that is directly held by the rat head [3]. Operated together with a mobility system that allows some freedom of the rat movements, behavioral studies could be performed while observing the functions of brain regions [4]. Nevertheless, in order to preserve the animal from any impediment to their motion activity during behavioral analysis, we have recently proposed a new fully autonomous telemetric miniaturized positron sensitive probe named PIXSIC (French acronym for ‘‘Pixellated Intracerebral Probe’’) [5]. The detector will be capable of performing in vivo analysis on awake and freely moving animals with high sensitivity and additional imaging features, while limiting stress induced in the animals during acquisition. The development of this new probe takes advantage of pixellated Silicon diode technology that has been extensively exploited in high energy physics experiments. Indeed, the properties of the high resistivity Silicon allow conceiving a low bias voltage operation sensor small enough to be implanted in rodent brain tissue, which can be combined with an autono- mous telemetric setup sufficiently miniaturized to be entirely worn by the rodent during the experiment. The specific detection conditions require a sensitive detector design suited to the Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/nima Nuclear Instruments and Methods in Physics Research A 0168-9002/$ - see front matter & 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2011.08.027 n Corresponding author. Tel.: þ33 169156230; fax: þ33 1697196. E-mail address: laniece@imnc.in2p3.fr (P. Laniece). Please cite this article as: M. Benoit, et al., Nucl. Instr. and Meth. A (2011), doi:10.1016/j.nima.2011.08.027 Nuclear Instruments and Methods in Physics Research A ] (]]]]) ]]]–]]]