Lower Iodine Load in Routine Contrast-Enhanced CT

OBJECTIVE: To demonstrate an alternative imaging strategy for routine thoracic computed tomography using low intravenous contrast volume. METHODS: Based on radiologists' clinical judgment, 61 thoracic computed tomographic examinations were performed using 15 mL of iohexol intravenous contrast. Indications included patients with relative con traindications to contrast, American College of Radiology appropriateness rating of 1 to 6 for contrast, rating of 7 or greater for contrast with a modifying condition, and cases without specific rating in which contrast may have been useful although not mandatory. Images were retrospectively reviewed to determine adequacy as part of an American Board of Radiology Practice Quality Improvement project. Ascending aorta and right and left pulmonary artery enhancement was measured and compared to most recent routine contrast protocol examination if available. RESULTS: All studies were adequate for evaluation of the given indication. Degree of vascular opacification was sufficient for discriminating between mediastinal structures. Computed tomography number (Hounsfield units) ± standard deviation using 15 mL of contrast compared to routine protocol was 134 ± 47.8 and 240.8 ± 86.6 in ascending aorta, 109.6 ± 47.6 and 185 ± 59.3 in right pulmonary artery, and 112 ± 50 and 186 ± 56.3 in left pulmonary artery, respectively. Mean difference in computed tomography number was significant. Low contrast dose studies demonstrated relatively decreased soft tissue enhancement. CONCLUSIONS: The 15-mL protocol results in reduced vascular and soft tissue enhancement; however, reasonable-quality images are obtained that are diagnostic for a wide range of indications, namely, those involving thoracic inlet, mediastinal, and hilar structures.