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Measurement of Renal Extraction Fraction with Contrast-enhanced CT¹

¹ From the Department of Radiology, Stanford University School of Medicine, 300 Pasteur Dr, Rm H1307, Stanford, CA 94305 (G.S., E.W.O., L.C., P.S.); Palo Alto Veterans Administration Medical Center, Palo Alto, Calif (E.W.O.); and Department of Radiology, University of California, San Diego (R.R.S.). Received August 6, 2004; revision requested October 14; revision received November 8; accepted December 15. Address correspondence to G.S. (e-mail: gsommer{at}stanford.edu).

Study was approved by the institutional review board, and informed patient consent was waived. A method for minimization of sources of variability in measuring single-kidney extraction fraction (EF) was determined retrospectively with contrast material–enhanced computed tomography (CT). Ten adults underwent CT of the kidneys; precontrast scans were obtained, followed by postcontrast scanning 2 minutes after contrast material injection. Single-kidney EF was then calculated for each patient with the formula EF = (CT_A – CT_V)/(CT_A – CT_PRE), where CT_A and CT_V are the postcontrast CT values (in Hounsfield units) of the systemic blood and renal venous blood, respectively, and CT_PRE is the precontrast CT value of the blood. Both conventional two-dimensional and volumetric three-dimensional regions of interest were used for determining mean CT values of the blood. By using the volumetric regions of interest, left and right renal EF values averaged 17.3% and 18.0%, respectively, for two observers, compared with the accepted value of 15%–20%. This latter technique also minimized right-left kidney and interobserver variability in the measurement of EF.

© RSNA, 2005

This article has been cited by other articles:

				F. G. Sommer Can Single-Kidney Glomerular Filtration Rate Be Determined with Contrast-enhanced CT? Radiology, February 1, 2007; 242(2): 325 - 326. [Full Text] [PDF]