Quantification of single-kidney glomerular filtration rate with electron-beam computed tomography

The ability to accurately and noninvasively quantify single-kidney GFR could be invaluable for assessment of renal function. We developed a model that enables this measurement with EBCT. To examine the reliability of this method, EBCT renal flow and volume studies after contrast media administration were performed in pigs with unilateral renal artery stenosis (Group 1), controls (Group 2), and simultaneously with inulin clearance (Group 3). Renal flow curves, obtained from the bilateral renal cortex and medulla, depicted transit of the contrast through the vascular and tubular compartments, and were fitted using extended gamma-variate functions. Renal blood flow was calculated as the sum of products of cortical and medullary perfusions and volumes. Normalized GFR (mL/min/cc) was calculated using the rate (maximal slope) of proximal tubular contrast accumulation, and EBCT-GFR as normalized GFR * cortical volume. In Group 1, the decreased GFR of the stenotic kidney correlated well with its decreased volume and RBF, and with the degree of stenosis (r = -0.99). In Group 3, EBCT-GFR correlated well with inulin clearance (slope 1.1, r = 0.81). This novel approach can be very useful for quantification of concurrent regional hemodynamics and function in the intact kidneys, in a manner potentially applicable to humans.