Measuring single-kidney glomerular filtration rate on single-detector helical CT using a two-point Patlak plot technique in patients with increased interstitial space.

OBJECTIVE We measured the single-kidney glomerular filtration rate (GFR) with a two-point Patlak plot technique based on multiphasic CT in patients with hydronephrosis or pyelonephritis or both. The question we sought to answer in our study was, Does increased interstitial space as measured with the Patlak plot technique cause overestimation of GFR? SUBJECTS AND METHODS Twenty adult patients treated with percutaneous nephrostomy were studied. The CT protocol consisted of an unenhanced scan and three subsequent scans obtained 38, 71, and 102 sec after the initiation of the contrast medium injection. Plasma clearance of the contrast medium was determined and used as the reference. Additionally, single-kidney excretory clearance was determined by separate urine collections from the left and right kidneys. A three-compartment model calculation was made using all data available to estimate volume and transfer rate constant of the interstitial space. RESULTS The GFR determined using plasma clearance correlated well with the GFR determined using excretory clearance, with a correlation coefficient of r = 0.94 and a regression line of y = -6 + 0.97 x x. GFR of both kidneys as measured using CT was overestimated according to the GFR determined using plasma clearance, with a correlation coefficient of r = 0.80, and a regression line of y = 35 + 0.79 x x. Single-kidney excretory clearance GFR was similarly overestimated using single-kidney CT GFR, with a correlation coefficient of r = 0.81 and a regression line of y = 20 + 0.84 x x. Single-kidney parenchymal volume was used as an indicator of interstitial space enlargement. The overestimation of excretory clearance GFR using CT correlated significantly with the parenchymal volume of the individual kidneys. A high correlation was also found between overestimation of total GFR determined with CT and interstitial space estimated using a three-compartment model calculation. Relative interstitial space was estimated to be 25% (range, 9-46%) of total kidney volume. CONCLUSION Using the interstitial space as a third compartment may introduce an error into the measurement of GFR with the Patlak plot technique. We found that the CT protocol in our study resulted in considerable overestimation of GFR as determined with the Patlak plot in patients with increased interstitial space.

[1]  Peters Am,et al.  Graphical analysis of dynamic data: the Patlak-Rutland plot. , 1994 .

[2]  David O. Cosgrove,et al.  Textbook of Contrast Media , 1999 .

[3]  N. Hackstein,et al.  Measurement of single kidney contrast media clearance by multiphasic spiral computed tomography: preliminary results. , 2001, European journal of radiology.

[4]  M. Blomley,et al.  The quantification of renal function with enhanced computed tomography , 1996 .

[5]  A. Peters,et al.  Functional Imaging in Computed Tomography: The Use of Contrast‐Enhanced Computed Tomography for the Study of Renal Function and Physiology , 1993, Investigative radiology.

[6]  Y. Tsushima,et al.  Use of contrast-enhanced computed tomography to measure clearance per unit renal volume: a novel measurement of renal function and fractional vascular volume. , 1999, American journal of kidney diseases : the official journal of the National Kidney Foundation.

[7]  C S Patlak,et al.  Graphical Evaluation of Blood-to-Brain Transfer Constants from Multiple-Time Uptake Data , 1983, Journal of cerebral blood flow and metabolism : official journal of the International Society of Cerebral Blood Flow and Metabolism.

[8]  S. Robbins,et al.  Pathologic basis of disease , 1974 .

[9]  D. Altman,et al.  STATISTICAL METHODS FOR ASSESSING AGREEMENT BETWEEN TWO METHODS OF CLINICAL MEASUREMENT , 1986, The Lancet.

[10]  M D Rutland,et al.  A single injection technique for subtraction of blood background in 131I-hippuran renograms. , 1979, The British journal of radiology.

[11]  P Dawson,et al.  Dynamic Contrast Bolus Computed Tomography for the Assessment of Renal Function , 1993, Investigative radiology.

[12]  N. Hackstein,et al.  Contrast media clearance in a single kidney measured on multiphasic helical CT: results in 50 patients without acute renal disorder. , 2002, AJR. American journal of roentgenology.

[13]  Y. Tsushima,et al.  Determination of glomerular filtration rate per unit renal volume using computerized tomography: correlation with conventional measures of total and divided renal function. , 2001, The Journal of urology.

[14]  M. Lipton,et al.  Contrast Bolus Dynamic Computed Tomography for the Measurement of Solid Organ Perfusion , 1993, Investigative radiology.

[15]  H. Osswald,et al.  Acute renal failure in man: new aspects concerning pathogenesis. A morphometric study. , 1990, American journal of nephrology.