Measurement of body potassium. Calibration and intercomparison of two whole-body radiation counters

The potassium contents of 13 men and 12 women have been estimated by measuring the rate of emission from the body of γ-rays from the natural radioisotope ⁴⁰K. Measurements were made with two whole-body radiation counters. The counting-rates from each subject were measured before and after an oral dose of ⁴²K. From these observations a calibration factor, F (gK/count per min), and an estimate of body potassium, were calculated for each counter.

The observed differences in the pairs of potassium estimates may occur because ⁴²K is not completely in equilibrium with the natural potassium in the body at the time of the second measurement, which was made 18-23 hours after administration of the dose.

The calibration factor, F, varies with the weight W, and height H, of the subject, and the regression coefficients of F on W, on W and H, on (W/H) and on (W/H)^1/2 have been calculated. The regression formulae can be used to predict the values of F for any subject of known height and weight.