Benefit of iodine density images to reduce out-of-field image artifacts at rapid kVp switching dual-energy CT

Abstract

Purpose To evaluate the reduction of out-of-field artifacts caused by body parts outside the field of view (FOV) at rapid kVp switching dual energy CT (rsDECT). Materials and methods This retrospective study was approved by our institutional review board. Informed consent was not required. We viewed 246 consecutive rsDECT thoracoabdominal scans to identify those with body parts outside the maximal FOV of 50 cm. The maximal length, thickness and subjective severity of the out-of-field artifacts were recorded for the 40, 65 and 140 keV virtual monochromatic and the iodine and water density images. Artifact severity was rated on a 5 point scale from 0=absent to 5=obscures intraabdominal/intrathoracic anatomic detail. Artifact thickness and severity scores were compared by t-test and Wilcoxon tests, respectively. Results In 20 of 246 scans (8.1%), body parts extended past the maximum FOV of 50 cm. The mean BMI of these 20 patients was 40.2 kg/m2 (range, 26.83 to 61.69 kg/m2), and out-of-field artifacts occurred for all 20. The mean out-of-field artifact maximal length was 16.6 cm. The mean artifact thickness was significantly less for iodine density (0.6 mm) than for the 65 keV and water density images (8.4 and 13.5 mm, respectively, p<0.001 each comparison). The mean artifact severity score was lower for iodine density (0.2) than for the 65 keV and water density images (2.5 and 2.6, respectively, p<0.001 each). Conclusion Iodine density images reduce out-of-field image artifact at rsDECT and assists in the evaluation of peripheral tissues that extend beyond the maximal CT FOV.