Subcutaneous measurements of 133Xe disappearance with portable CdTe(Cl) detectors: elimination of interference from combined convection and diffusion.

Portable, solid state, cadmium telluride [CdTe(C1)] detectors were used for measurements of 133Xe-disappearance rate constants as a measure of subcutaneous (s.c.) blood flow. To eliminate the disturbance on the measurements from combined local convection and diffusion of xenon in the s.c. tissue, two methods were demonstrated to be feasible in both control persons and anaesthetized rabbits. A small volume (50-80 microliters) was injected into the s.c. tissue at a depth of 5 mm and the CdTe(C1) detector elevated 20 mm above the skin surface. In this situation identical disappearance rate constants were recorded by the CdTe(C1) detector and the NaI(T1) reference detector at 15-20 cm from the depot. Similiar results were obtained when either a large volume (greater than or equal to 800 microliters of Xe in humans) was injected into the s.c. tissue or the labelling was performed with a smaller volume in an atraumatic uniform manner to obtain a constant Xe concentration exceeding the field of view of the CdTe(C1) detector, which in these cases was attached directly to the skin surface. The coefficients of variation (CV) of the disappearance rate constants measured by the CdTe(C1) detector were 9% and 11%, and these values did not differ significantly from each other (P greater than 0.2), or from CV-values calculated from measurements with NaI(T1) detectors.