CT angiography for pulmonary embolism detection: the effect of breathing on pulmonary artery enhancement using a 64-row detector system

Abstract

Computed tomography pulmonary angiography (CTPA) is used most often in routine clinical practice for the assessment of a suspected pulmonary embolism. The diagnostic accuracy relies on sufficient contrast enhancement. To evaluate whether image acquisition during shallow breathing can improve the image quality in patients with insufficient contrast enhancement during breath-hold examinations. A total of 2786 CT pulmonary angiographies, acquired on a 64-row CT during deep-inspiration breath-hold, were reviewed. Twenty-four examinations were considered non-diagnostic due to poor contrast enhancement in the pulmonary arteries (PA), although they showed preserved vascular enhancement of the superior vena cava (SVC) and the ascending aorta (AO). Eleven flawed CTPA examinations, including severe breathing artifacts and incorrect triggering were excluded. In 13 of the remaining patients, the examination was repeated during shallow breathing. Vascular contrast enhancement was compared between both scans by measuring the relative enhancement within the SVC, the main PA, and the AO. Image quality was scored by two, clinically experienced radiologists. The values are given as median and [25th;75th] quartile. There was a significant difference in the CT values for the PA between the repeated scans (P = 0.0002, Wilcoxon test), and with the CTPA in deep-inspiration showing a median enhancement of 97 HU (59-173), compared with 303 HU (239-385) in the CTPA acquired during free breathing. The differences for both the AO (P = 0.54) and the SVC (P = 0.78) were not significant. Scoring for the attenuation quality rose significantly (P = 0.0002) and no severe motion artifacts were detected on either scans. If there is insufficient pulmonary artery enhancement during CTPA, attenuation of the pulmonary arteries can be improved by acquisition during shallow breathing and is without significant loss of the overall diagnostic image quality.