QUANTIFICATION OF RENAL UPTAKE OF TECHNETIUM-99M-DTPA USING PLANAR SCINTIGRAPHY - A TECHNIQUE THAT CONSIDERS ORGAN VOLUME

We developed a method to estimate the radioactivity of Tc-99m-DTPA wit hin the kidney by planar scintigraphy. Phantom experiments and renal s tudies were used to compare our method with that of the Gates' method. Our method corrects for scatter and attenuation using the volume dept h-independent buildup factor technique, after which background correct ion is performed with consideration for target organ volume. When the renal phantom-to-background activity concentration ratio (S) was chang ed from 5 to 80 in a water-filled container and the renal phantom dept h was varied from 1 to 11 cm for each value of S, the renal phantom co unt rate calculated by our method was accurate under all conditions in vestigated. In contrast, the Gates' method was significantly affected by phantom depth and S values. In 40 patients, renal uptake in the ima ge obtained 2-3 min after injection of Tc-99m-DTPA was estimated by ou r method and the Gates' method, and the correlation between uptake and creatinine clearance was determined. When a ring background region of interest (ROI) around the kidney was employed, a good correlation was obtained by our method (r = 0.947) in comparison with the Gates metho d (r = 0.887). With both methods, a semilunar background ROI produced poor results than the ring background ROI. In conclusion, renal radioa ctivity levels that correlate well with creatinine clearance can be ob tained by our method, which allows estimation of individual glomerular filtration rates.