RENAL DEPTH ESTIMATES TO IMPROVE THE ACCURACY OF GLOMERULAR-FILTRATION RATE

This study was performed to validate a computer implementation of the Gates' method for radionuclide glomerular filtration rate (RGFR) calcu lation. The accuracy of the original method was improved by replacing the Tonnesen formula that estimated renal depth with direct measuremen t from lateral views to calculate tissue attenuation correction. Metho ds: Both the creatinine clearance test (CCT) and dynamic Tc-99m-diethy lenetriamine pentaacetic acid (DTPA) renal scintigraphy (DRS) weve per formed on 38 patients on the same day. RGFR was quantified from the at tenuation corrected absolute DTPA uptake of the kidneys on DRS from 12 0-180 sec after injection. Attenuation correction was estimated using the lateral views of the kidneys taking in account the distance from t he computed geometric center of the kidneys to the posterior body surf ace along a line vertical to the collimator surface. CCT and glomerula r filtration rate estimates from DRS were compared by linear regressio n. Results: RGFR estimates agreed well with CCT, yielding a correlatio n coefficient of 0.92 in 38 patients and 0.90 in a subgroup of 11 pati ents suffering from chronic renal failure. Conclusion: Present modific ations improve RGFR accuracy to the precision range of blood sample ba sed methods. This modified method requires little additional work and no extra cost in patients undergoing DRS. RGFR calculation may be adva ntageous in cases when 24-hr urine collection for CCT cannot be obtain ed, and it should improve the accuracy of the captopril test.