Nuclear Instruments and Methods in Physics,b

erm teco 30 ati l m ET vie messengers and carriers, is often smaller than 12 15 1 imaging investigation [2]. size of the objects under study (small organs or brain than 4–6mm FWHM. For example, the imaging of the rat brain requires a spatial resolution less than 2mm FWHM, while for mice it would be ideal to use instruments with a ARTICLE IN PRESSresolution less than 1mm FWHM (Fig. 1). In addition, high-sensitivity instrumentation is required when fast dynamic processes (with characteristic time o