Quantitative in vivo measurements of tumor perfusion using rubidium-81 and positron emission tomography

Rubidium-81 (t1/2 = 4.58 hr) was investigated as a tumor perfusion tracer in the VX2 carcinoma implanted into rabbit thigh muscle using a large-area, multiwire proportional chamber positron emission tomography (PET) system. Perfusion was determined using the arterial reference sample method, and the results from PET imaging were compared with postmortem tissue sampling. Absolute quantitation of tumor perfusion was achieved using external probes to estimate local extraction fraction. Redistribution of rubidium-81 (81Rb) was investigated using a dual-tracer technique. Average perfusion was found to be 13.5 and 3.7 ml/min/100 g in tumor and normal muscle, respectively. The extraction fraction as estimated from a two-compartment model ranged from 0.94 to 1.00. No significant redistribution of 81Rb was observed in these tissues. Nine patients with malignancies were studied using 81Rb and PET. Tumor perfusion in four patients with carcinoma of the breast was elevated by a factor of 1.8 (range 1.2-2.3) compared to contralateral normal breast.