A single tracer method for background subtraction in 197HgCl2 renal uptake measurements

The 197HgCl2 renal uptake was measured in 70 patients in order to study the degree of the background activity and to determine the best correction method. The deduction of background activity was made: a) From a concentric perirenal region of interest with no additional correction. b) Using a double tracer technique with colloid 99mTc, subtracting consecutively the liver and spleen activity and the residual background. Comparison of the results revealed: a) The correction of background activity significantly altered the uptake estimations, and thus must include both the liver and spleen activity, and the residual background. b) The choice of a median region of interest for the residual background evaluation led to a systematic error. c) The assessment of background activity, based upon a perirenal region of interest provided a sufficiently precise and reliable correction of the total background, while avoiding the inconveniences associated with the double tracer method.