Contrast enhancement in abdominal CT: bolus vs. infusion.

The accuracy of in vivo iodine estimations by CT in the aortic blood was determined in the dog. Iodine wash-out curves of five patients each receiving either a bolus of 100 ml diatrizoate 60% or a 10 min infusion of 300 ml diatrizoate 30% and 138 nonenhanced abdominal CT scans with various lesions in 104 patients were analyzed. This investigation suggests: (1) In vivo estimations of iodine concentrations are subject to considerable variation. (2) Iodine accumulation and wash-out for a given contrast administration mode are similar in liver, spleen, and pancreas with tissue iodine concentrations always below blood iodine concentrations, while a significant iodine concentration above iodine blood levels is found in the renal parenchyma. (3) If contrast enhancement is analyzed separately for bolus effect (arteriovenous iodine difference [AVID] greater than 30 H), nonequilibrium phase (AVID 10-30 H) and equilibrium phase (AVID less than 10 H), a good correlation between aortic blood and tissue iodine concentration is found for the latter two phases in the kidney, liver, and spleen which is independent of the contrast administration mode. (4) Visualization of all focal (cystic and solid) lesions is improved in the kidneys after contrast enhancement, while in the other investigated abdominal organs only cystic lesions are always better visualized on the enhanced scan regardless of contrast material dose, administration mode, and time of scanning. (5) Improved visualization of a solid lesion in liver, spleen, and pancreas is most likely achieved by scanning during bolus effect and the nonequilibrium phase, that is, within the first 2 min after a contrast material bolus or during a contrast material infusion. The chance to conceal a lesion in these organs increases significantly when performed at a later stage after contrast administration, that is, in the equilibrium phase.