Functional CT of the kidney.

The iodinated contrast agents used for computed tomography (CT) are filtered at the glomerulus and not reabsorbed by the tubules and have pharmacokinetics comparable to inulin. They can thus measure physiological indices such as contrast clearance per unit volume, which is closely related to glomerular filtration rate per unit renal volume of kidney, after due allowance for the difference between blood and plasma clearance. In this review, we show how dynamic CT can be used to measure both regional and global blood clearance of contrast material. A single slice of kidney is scanned sequentially after bolus intravenous (i.v.) injection of contrast material. Next, time-attenuation curves are constructed and contrast clearance per unit volume is calculated using a Patlak graphical analysis. CT determination of renal volume is made and global contrast clearance can be then also calculated. In normal kidneys, clearance/volume averaged 0.49+/-0.11 ml min(-1) ml(-1) (mean +/- S.D.), and these values agreed with literature data obtained using other techniques. A negative correlation between patient's age and clearance/volume was seen. A strong correlation was observed between creatinine whole blood clearance and the global contrast clearance (the product of renal volume determined by CT and contrast clearance/volume). Dynamic CT can provide quantitative renal physiological information on a regional basis non-invasively.