Effect of background correction on separate technetium-99m-DTPA renal clearance

The estimation of the background constitutes the main difficulty in the accurate determination of the separate renal clearance, using the 99mTc-DTPA complex and the gamma camera. This is due to the low extraction rate of DTPA, giving an unfavorable signal-to-noise ratio, and to the fact that no background area can accurately represent both interstitial and vascular components of the renal curve. Several algorithms have been proposed in the literature for solving the problem of background but their effect on the calculated clearance value has not been sufficiently assessed. In this paper, it has been possible, using a theoretical approach, to predict the respective influence of the different algorithms on the renal clearance. These results were confirmed on the basis of clinical data obtained from 53 renal studies. It was shown that a double background correction, using successively the area ratio method followed by a linear fit method, is probably the most precise method and is less dependent on the choice of the background area.