Determination of Glomerular Filtration Rate with CT Measurement of Renal Clearance of Iodinated Contrast Material versus 99m Tc-DTPA Dynamic Imaging "Gates" Method: A Validation Study in Asymmetrical Renal Disease

Purpose To validate a computed tomographic (CT) glomerular filtration rate (GFR) measurement and compare it with renal dynamic imaging GFR obtained by using the "Gates" method, with dual plasma sampling technetium 99m ( Tc) diethylenetriaminepenta-acetic acid (DTPA) clearance ("true GFR") as the reference standard. Materials and Methods This prospective study was approved by the institutional review board, and written informed consent was obtained from all patients. Forty-two patients with unilateral renal disease were included. Single-kidney CT GFR was calculated as excretory phase whole-kidney CT number enhancement divided by the area under the time-attenuation curve for the aorta, multiplied by (1 - hematocrit level). The CT GFR was then obtained by summing the result of the two sides. The true GFR and the Gates GFR were measured by using a single injection of Tc-DTPA. The CT GFR and Gates GFR were respectively compared with the true GFR by using a paired t test and linear regression analysis. Results The difference between CT GFR (mean ± standard deviation, 96.02 mL/min ± 23.11) and true GFR (90.50 mL/min ± 21.46) was 5.51 mL/min ± 6.96 (P < .001), demonstrating 6.09% systemic overestimation. The difference between Gates GFR (93.93 mL/min ± 26.97) and true GFR was 3.42 mL/min ± 16.10 (P = .176). Linear regression findings confirmed the association between CT GFR (y-axis) and true GFR (x-axis) and between Gates GFR (y-axis) and true GFR (x-axis) (P < .001 for both). Both regression lines paralleled the diagonal (intercept = 0 and slope = 1) (P = .599 and P = .945, respectively). The 95% confidence interval of the former was above the diagonal, confirming the systemic overestimation. The standard deviations of residuals of both linear regressions were 7.02 mL/min and 16.30 mL/min, respectively, demonstrating smaller deviation of the CT GFR (P < .001). Conclusion The proposed CT GFR measurement was validated in this study and was proved to be more accurate than the Gates method despite slight (6.09%) systemic overestimation. RSNA, 2016 Online supplemental material is available for this article.