The gamma camera as an absolute measurement device: determination of glomerular filtration rate in 99mTc-DTPA renography using a dual head gamma camera.

AIM: The aim of this study was to design a general nuclear medicine method for fast, accurate and direct determination of the clearance of a radioactive indicator provided that all uptake compartments of the radioactive indicator could be included in the field of view of the gamma camera.
METHODS: The data material for clearance calculation in the gamma camera method (GCM) comprises: (1) a transmission map of a part of the body using a water filled flood field phantom with a uniform distribution of the radioisotope, (2) the background corrected activity curves in the anterior and posterior views over all uptake compartments following the injection of the radioactive indicator, and (3) the activity of the radioactive indicator in at least two blood samples drawn during the examination. With a view to determining glomerular filtration rate (GFR) in 99mTc-DTPA renography the gamma camera method was tested in a group of 26 adult subjects in whom GFR was determined simultaneously using the simplified multiple samples method (MSM) with plasma samples drawn 3-5 h following the injection of 51Cr-EDTA.
RESULTS: For values of GFR above 30 ml.min(-1) the regression line of GFR in the MSM versus GFR in the GCM was not significantly different from the line of identity. The reliability of the GCM alone was about 14%, 11% and 6% for GFR values of 30, 60 and 120 ml.min(-1) and, therefore, the reliability of the GCM and the simplified MSM for prediction of GFR was almost the same.
CONCLUSION: Since the recording of the renal count rates in the anterior and posterior views permits an accurate determination of the split renal function, the GCM yields reliable estimates also of the single kidney GFR.