Functional CT of the kidney

The iodinated contrast agents used for computed tomography (CT) are filtere d at the glomerulus and not reabsorbed by the tubules and have pharmacokine tics comparable to inulin. They can thus measure physiological indices such as contrast clearance per unit volume, which is closely related to glomeru lar filtration rate per unit renal volume of kidney, after due allowance fo r the difference between blood and plasma clearance. In this review, we sho w how dynamic CT can be used to measure both regional and global blood clea rance of contrast material. A single slice of kidney is scanned sequentiall y 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. I n normal kidneys, clearance/volume averaged 0.49 +/- 0.11 mi min(-1) ml(-1) (mean +/- S.D.), and these values agreed with literature data obtained usi ng other techniques. A negative correlation between patient's age and clear ance/volume was seen. A strong correlation was observed between creatinine whole blood clearance and the global contrast clearance (the product of ren al volume determined by CT and contrast clearance/volume). Dynamic CT can p rovide quantitative renal physiological information on a regional basis non -invasively. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.