Contrast Bolus Dynamic Computed Tomography for the Measurement of Solid Organ Perfusion

Abstract

The authors have investigated the aortic responses to various intravenous bolus injections of nonionic and ionic contrast media and have presented data illustrating the potential of ultrafast computed tomography (CT) to quantify perfusion in the kidney, liver, and spleen. Bolus Dynamics Study: Performed in 3 healthy dogs (weight: 35 kg to 36 kg). In 2 dogs, 15 mL of the nonionic agent iohexol and the ionic agent sodium-meglumine diatrizoate were injected at 5, 10 and 20 mL/sec via a venous catheter placed in the superior vena cava; the order of injection was alternated between the 2 dogs. In the third dog, 25 mL of iohexol 300 mg I/mL was compared with diatrizoate 370 mg I/mL with injection rates of 10 and 20 mL/sec. Computed tomography scanning at the level of the midabdominal aorta was performed using an ultrafast CT scanner. Time-density curves were drawn for regions of interest over the aorta, and gamma-variate fits performed. Perfusion Studies: Dynamic perfusion scans of the upper abdomen were performed in more than 50 patients. A dose of 25 mL of iohexol 300 mg I/mL was injected at 10 mL/sec via an intravenous cannula in the antecubital fossa, followed immediately by 25 mL of saline, at the same rate. Scanning was performed at a single level using an ultrafast CT scanner. Regions of interest were drawn and gamma-variate fits were applied to the vascular time-density curves. Bolus Dynamics: Excellent curve fits for aortic time-density curves were obtained. A 10-mL/sec versus a 5-mL/sec bolus produced an 8% higher peak density. Nonionic contrast increased the peak density by a mean of 6%, increased the area under the corrected time-density curve by a mean of 22%, and lengthened the increase time by a mean of 21%. Perfusion Studies: Values obtained were reproducible and correlated well with values predicted from inert gas washout techniques. Changes in the CT number in a region after an intravenous injection of contrast medium may be used to calculate blood flow per unit volume of tissue. Ultrafast CT offers sufficient data points for accurate calculation. The quality of the aortic bolus is of great importance. Nonionic media offer several important advantages: hemodynamic perturbation is minimized, and they are better tolerated at the high injection rates needed. Low-osmolality nonionic agents produce "better" curves than conventional high-osmolality ionic agents, all other factors being equal. The resulting data are relevant to intravenous digital subtraction angiography and indirect portography as well as to perfusion measurement. The technique of quantitative dynamic CT is theoretically applicable to any cross-sectional modality, notably magnetic resonance.