Evaluation of a commercial radiochromatography module as an arterial blood activity monitor

Input functions required for positron emission tomography (PET) tracer kinetic modeling are often obtained from arterial blood. In some situations, using short-lived radiotracers, e.g. [(15)O]water, rapid sample handling is required. A method used at several facilities is to pump blood through a detector system at a constant rate. We investigate the suitability of a commercial radiochromatography module (IN/US Posi-RAM) for this new use. The Posi-RAM consists of two 2.5 cm (length) x 2.5 cm (diameter) cylindrical bismuth germanate (BGO) detectors that can operate in coincidence mode. Arterial blood is transported through the system via a length of tubing with flow rate controlled by a peristalsis pump. A custom-counting loop and support frame were designed for the Posi-RAM for PET studies. System sensitivity was determined to be 1.1 x 10(4) cps/(MBq ml(-1)). Dead time as a function of count-rate was found to be less than 1% for concentrations below 3.5 MBq ml(-1), a range encompassing all human-study values. In a human study, the performance of the device was found to be similar to that of the facility's current blood monitor (Siemens Fluid Monitor). We conclude that the Posi-RAM has the necessary sensitivity and count-rate capabilities to be used as a real-time blood activity monitor.