Quantifying tumour uptake of the blood flow tracer copper(II) pyruvaldehyde bis(N-4-methylthiosemicarbazone) (Cu-PTSM) with a multiwire proportional chamber positron camera (MUP-PET)

The physical decay of Cu-62 (half-life = 9.74 min) results in a significant reduction in activity over image acquisition times required to calibrate the voxel count directly with a multiwire proportional chamber positron camera (MUP-PET). A method of image quantification on a voxel by voxel basis was developed using measured data rates on the detectors at the start of image acquisition. The method is valid for radiotracers with no biological redistribution and where all the activity is in the imaging field of view (FOV). Regional infusion of the perfusion tracer Cu-62-PTSM via the hepatic artery with high first pass extraction in the liver fulfils these criteria. The extraction fraction can be determined to within +/-10%. The precision with which the percentage injected dose per millilitre of tissue can be determined is related to the voxel count. The voxel count is a complex function of radiotracer distribution and total acquired coincidence events. Standard deviations on tissue measurements for selected regions of tumour and normal liver indicate this is in the order of +/-10-20% for (0.8-1) x 10(6) acquired coincidence events. We are currently measuring changes in tumour and normal liver perfusion in response to regional angiotensin II infusion using this technique.