THE QUANTIFICATION OF RENAL-FUNCTION WITH ENHANCED COMPUTED-TOMOGRAPHY

The changes with time in renal parenchymal and vascular attenuation fo llowing injection of an intravascular contrast medium can be exploited to study renal physiology in several ways. Shortly after injection, b oth contrast medium clearance and fractional vascular volume per unit volume of kidney can be measured on a regional basis by obtaining sequ ential CT data from one anatomical level and the application of a grap hical analysis to the baseline subtracted CT numbers for tissue and va scular regions of interest: c(t) and b(t), respectively. By plotting t he ratio c(t)/b(t) against integral b(t)dt/b(t), both fractional vascu lar volume and contrast medium clearance can be estimated graphically. At later time points, a semilogarithmic plot against time of the decl ining attenuation of vascular or parenchymal regions of interest gives information about overall, as opposed to regional, renal function: th e gradient estimates the glomerular filtration rate per unit volume of extracellular fluid. Absolute glomerular filtration rates can also be calculated with blood sampling. Although further experimental evaluat ion is needed, these techniques have a strong theoretical basis, and e xperimental work performed so far is encouraging. Possible application s of these techniques are discussed.