CALIBRATION OF A TOTAL-BODY POTASSIUM MONITOR WITH AN ANTHROPOMORPHICPHANTOM

An anthropomorphic phantom was used to calibrate a supine geometry sod ium iodide total body potassium monitor. Correction factors accommodat ing variability in subject size were empirically determined. Measureme nts on 12 males of weight 45-96 kg, height 161-184 cm and 18 females o f weight 48-89 kg, height 153-175 cm, showed that the K-40 calibration factor (F, counts s(-1) (g of potassium)(-1)) was significantly corre lated (r = 0.88, p < 0.0001) to subject (weight/height)(0.5), indicati ng comparable accuracy to K-42-based calibration procedures. Fat-free mass determined from the potassium measurements of 16 subjects correla ted significantly with fat-free mass estimated from skinfold thickness (r = 0.98, p < 0.0001), dual-energy x-ray absorptiometry (r = 0.99, p < 0.0001) and bioimpedance analysis (r = 0.98, p < 0.0001). These dat a, together with the precision (coefficient of variation, CV = 1.5%) a nd accuracy (CV = 4.5%) of the system, indicate that this calibration procedure represents a relatively low-cost, non-invasive alternative t o K-42-based methods of calibrating total body potassium monitors.