Utilities of dynamic scanning in cardiac computed tomography

Dynamic CT scanning comprises the rapid repetition of scans with the shortest interscan time at the same level. We applied this scanning with injection of iodine contrast medium for evaluation of cardiac output and shunt ratio. 1. Cardiac output When dynamic scanning was performed at the level of the main pulmonary artery with bolus injection of contrast medium from the peripheral vein, the dilution curve could be obtained from the change of CT numbers in the great vessels. Consequently, if total volume of contrast medium and correlation between CT numbers and concentration of the contrast are known, cardiac output could be calculated according to the principle of dilution method. 2. Shunt ratio When contrast was injected continuously from the peripheral vein with constant flow rate, the early equilibrium of concentration is obtained in each portion of the great vessels depending on blood flow, and this equilibrium was achieved immediately after the appearance of contrast. Therefore, if dynamic scanning was performed at the level of the main pulmonary artery following the injection of the contrast from the antecubital vein, and CT numbers of the superior vena cava, pulmonary artery and aorta in early equilibrium phase were obtained, both left-to-right and right-to-left shunt ratios and Qp/Qs could be calculated from dilution rate of the contrast on the assumption that the ratio of flows in the superior and inferior vena cava is 3 : 2