CdTe-detector registration of 99mTc-DTPA clearance

Since the most essential function of the kidneys is to regulate the composition and volume of the extracellular fluids the ratio of the extracellular volume (ECV) to the glomerular filtration rate (GFR) seems to be a relevant index of kidney function. This ratio is equal to the mean transit time ( \(\overline t\) ) of an injected ECV-distributed tracer that is exclusively eliminated from the body by glomerular filtration. In 26 patients \(\overline t\) was estimated by means of standard methods after an intravenous injection of ^99mTc-DTPA and was found to be correlated (r=0.98) to the reciprocal final slope of the time-activity curve obtained by means of small CdTe-detectors pasted laterally on the crus, 10–12 cm below the knee joint. It is concluded that this external measurement of kidney function, without blood sampling, may shorten the usual procedure from 4 to 1 h. Furthermore, due to the constant detection geometry throughout the investigation it may provide the means for prolonged continuous monitoring of the kidney function at steady state and when rapid changes are expected.