If multislice CT (MSCT) of the liver is to yield optimal images, sufficient contrast (meaning an adequate amount of iodine) must be used. The degree to which a hepatic lesion becomes conspicuous in an image is directly related to the grams of iodine present. Exploration of the benefits of using more highly concentrated contrast media began with the recent wide dissemination of MSCT capabilities.
Effective imaging of the liver requires approximately 150 mL of contrast medium at the standard iodine concentration of 300 to 320 mg/mL. The use of MSCT for imaging other areas of the body, on the other hand, has typically permitted a reduction in the amount of contrast required. For example, helical CT of the chest calls for 100 to 150 mL of iodinated contrast, but only 60 to 75 mL of the same contrast medium is needed for an MSCT examination of the same area. The more precise protocols necessary for imaging of the liver, however, mean that conducting studies without sufficient contrast medium will compromise the detectability of hepatic lesions.
At present, the prices charged by vendors for iodinated contrast media have little relationship to the concentration of iodine that is present, that is grams of iodine. Instead, cost is tied to volume. Therefore, it can be cost effective to use contrast media having a higher concentration of iodine because the total volume of contrast used for a particular examination will be reduced.
Contrast media with iodine concentrations of 350, 370, and 400 mg/mL are now in clinical use. By determining the necessary amount of iodine per study and using a lower volume of a more highly concentrated contrast medium to constitute that amount, an imaging facility can decrease its contrast costs. For example, the target range for liver imaging is 37 to 48 grams of iodine. At a concentration of 300 mg/mL, a 150-mL contrast volume would be needed, but only two thirds as much (100 mL) would be required at a concentration of 370 mg/mL or more.
If the contrast medium is more highly concentrated, the rate at which it is administered can also be reduced without compromising the grams of iodine delivered per second. If iodine is to be administered at 1.5 g per second, the delivery rate must be 5 mL per second for contrast containing 300 mg/mL of iodine. For a contrast medium containing 370 mg/mL of iodine, the administration rate can be reduced to 4 g per second. Alternatively, if desired an increased dose of iodine can be delivered by using higher concentration contrast material at the same rate.
By pairing the power of MSCT with the newer, more highly concentrated offerings of contrast manufacturers, imaging providers can produce maximal image quality for their patients at a lower cost than was previously possible.