Development of an On-Line Blood Detector System for PET Studies in Small Animals

This chapter presents reports on the development of a dedicated online blood detection system and its preliminary application, in conjunction with a dedicated small animal positron emission tomography (PET) scanner, to the measurement of glucose metabolism (CMR glu ) in the rat brain. The β + detector was composed of a shielded block of NE102A scintillating plastic, with a 1.6 mm diameter longitudinal hole, through which an arterial catheter was passed. The detector was optically coupled to a single 38 mm photomultiplier tube, and standard NIM electronics were used to shape, gate, and process the signal output. An ALT-386SX laptop PC was used to record the logic pulses. Ten male Sprague–Dawley rats are used, five of which were fed ad lib (fed) and five whose food was withdrawn overnight. Each rat was given [ 18 F]-fluorodeoxyglucose iv, and a 60 min dynamic scan is performed. Arterial blood is allowed to flow freely through the online β + detector at intermittent predetermined time intervals, throughout the study period. In addition, blood samples are collected manually and measured in a well counter, cross-calibrated with the scanner. It is found that there is a good correlation between the blood curve, as measured by the online detector, and the discrete blood samples. The online detector provided marked improvement in the definition of the peak. Plasma curves were generated and brain time-radioactivity curves were fitted to a two-tissue compartmental model using standard nonlinear regression techniques. Assuming a lumped constant of 0.58, CMR glu was 0.6 ± 0.1 and 0.7 ± 0.1 for fed and fasted animals, respectively.