SIC: an intracerebral radiosensitive probe for in vivo neuropharmacology investigations in small laboratory animals: prototype design, characterization, and in vivo evaluation

Several high-resolution tomographs dedicated to small animal imaging are presently under development. However, these devices are limited by two major drawbacks: their cost is high and they require animal anaesthesia and immobilization, thus restricting the scope of investigations. Therefore, we have developed SIC (French acronym for "Sonde IntraCerebrale") a low-cost beta microprobe for measuring local radioactivity in awake, freely moving animals. Besides good sensitivity, SIC offers the advantage of a high temporal resolution, a major asset for in vivo measurements of tracer kinetics. Furthermore, SIC can be readily combined with existing techniques such as electrophysiology, microdialysis, voltammetry and magnetic resonance imaging, providing simultaneous complementary information on cerebral function. We present here the design, manufacture, and evaluation of a SIC prototype. In vitro evaluation using a beaker filled with a homogenous aqueous solution of [/sup 18/F]-fluorodeoxyglucose (/sup 18/F-FDG) confirmed our Monte Carlo simulation results in terms of sensitivity and detection volume. Further in vivo studies on rats with two probes implanted in the brain validated the use of SIC to measure the local concentration of radio-labeled molecules in rat brain with a high temporal resolution.