Bone-Subtraction CT Angiography: Evaluation of Two Different Fully Automated Image-Registration Procedures for Interscan Motion Compensation

Abstract

BACKGROUND AND PURPOSE: Bone-subtraction techniques have been shown to enhance CT angiography (CTA) interpretation, but motion can lead to incomplete bone removal. The aim of this study was to evaluate 2 novel registration techniques to compensate for patient motion.

Contrast-enhanced magnetic resonance angiography in carotid artery disease: does automated image registration improve image quality?

“…This nonsignificant study result is, nonetheless, a positive finding for conventional carotid MRA since it confirms that carotid MRA is robust against naturally occurring body shifts. This is in contrast to subtraction CTA, where angiographic image quality was found to be decreased by such shifts that may occur between acquisition of the unenhanced and the contrastenhanced CTA sequences [8,9]. The study finding may be explained in the context of neck anatomy and corresponding MRA signal intensities: the T1-weighted MRA images are dominated by signals from contrast-enhanced neck arteries as well as from surrounding fatty tissue.…”

“…Multiplanar reformation allows a detailed analysis of individual arteries, particularly the quantification of luminal narrowing. However, without mask subtraction it is difficult to generate DSA-like images since bony anatomy and calcified plaque components frequently overlie the cervical arteries in radiographic projections, even after manual image segmentation [8,9,21]. Such DSA-like images may, however, still be useful to attending clinicians who are used to interpreting DSA images.…”

“…In this context it is noteworthy that CTA can also be used with mask subtraction whereby an unenhanced CTA data set is subtracted from a subsequently acquired contrastenhanced counterpart [8][9][10]22]. However, subtraction artefacts due to slight body shifts may occur between scans in such examinations [22].…”

“…However, subtraction artefacts due to slight body shifts may occur between scans in such examinations [22]. It has been shown that these artefacts may be eliminated and overall image quality of carotid subtraction CTA improved by image registration [8][9][10]. Furthermore, considering MRA in peripheral arterial disease, it has been shown that automated image registration may improve angiographic image quality significantly, specifically in the lower leg and in circumstances when a patient has shifted their legs by 1 mm or more between acquisition of the unenhanced and the contrast-enhanced MR sequences.…”

“…This socalled image registration intends to eliminate the effect of the patient's body shift, such that the final subtracted DSA images are ideally free of motion artefacts. The quality of carotid subtraction CTA can also be increased by image registration with the intention to eliminate high-density structures such as bones, calcified plaques or implanted stent material from the final angiographic images [8][9][10]. Furthermore, the angiographic quality of lower leg MRA may be improved by image registration if the patient has moved their legs by 1 mm or more between acquisitions of the unenhanced and contrast-enhanced sequences [11].…”