Focal iodine defects on color-coded iodine perfusion maps of dual-energy pulmonary CT angiography images: a potential diagnostic pitfall.

OBJECTIVE The purpose of this article is to systematically investigate focal iodine defects found in patients without other CT evidence for pulmonary embolism on color-coded iodine perfusion maps of dual-energy pulmonary CT angiography scans. SUBJECTS AND METHODS Forty-three patients (mean age, 56.9 years; range, 29-88 years) who underwent pulmonary CT angiography using dual-energy CT from November 2007 to February 2008 but who had no pulmonary embolism were included in our study. Dark orange- or black-colored areas on color-coded iodine perfusion maps were interpreted as focal iodine defects. Two radiologists recorded the presence, location, and characteristics of the focal iodine defects in consensus and evaluated the examinations with regard to the causes of the focal iodine defects. RESULTS Focal iodine defects were found in 41 patients (95%). The most commonly involved segments were the anterior segment of the right upper lobe (33/38, 86.8%), the apical segment of the right upper lobe (32/38, 84.2%), the medial segment of the right middle lobe (32/38, 84.2%), the apicoposterior segment of the left upper lobe (35/42, 83.3%), the superior and inferior lingular segments of the left upper lobe (23/42, 54.8%), and the medial-basal segment of the right lower lobe (11/32, 34.4%). Beam-hardening artifacts caused by contrast material in the superior vena cava accounted for nearly all defects in the apices of both upper lobes. Cardiac motion was the most common cause of defects in right middle lobe and left upper lobe lingular segments, and diaphragmatic motion was the most common cause in the lung bases. CONCLUSION Knowledge of the focal iodine defects not related to pulmonary embolism leads to more accurate interpretation of dual-energy pulmonary CT angiography scans.