A MICROVOLUMETRIC BLOOD COUNTER SAMPLER FOR METABOLIC PET STUDIES IN SMALL ANIMALS/

Quantitative metabolic imaging in small animals with positron emission tomography (PET) requires the determination of the tracer concentrati on in whole blood, arterial plasma and metabolites as a function of ti me, A blood counting and sampling system was designed to simultaneousl y measure the time-activity curve as microvolumes of blood are collect ed. The system consists of a flow-through counter made of a plastic sc intillator to detect positrons and of a computer-controlled blood samp ler based on the concept of bubble segmentation. The number and size o f samples, the withdrawal speed and the sampling time are programmable and can be modified on-line. Samples as small as 10 mu l can be repet itively obtained from an implanted arterial catheter in the femoral ve in or artery of small rats (150 g) or the jugular vein of mice (20 g). For medium sampling speed (100 mu l/min) at a constant rate, the stan dard deviation of the sample activity is typically less than 1%. By cu tting the tubing at the bubbles at the end of the experiment, samples are made available for further processing and biochemical analysis. Th is apparatus has become an essential tool for quantitative animal PET studies, allowing easy, reliable sampling at a low cost.