Sixty-four-section multidetector CT angiography of carotid arteries: a systematic analysis of image quality and artifacts.

BACKGROUND AND
PURPOSE: Sixty-four-section CT scanners have recently been introduced for vascular imaging. Before such scanners reach widespread use, scanning protocol should be optimized and image quality assessed. The goals of this study were to systematically measure image quality and determine the prevalence of various types of artifacts produced by a 64-section scanner.
MATERIALS AND METHODS: We retrospectively reviewed CT angiography (CTA) scans obtained on a 64-section CT scanner in 100 consecutive patients presenting to the emergency department during a 2-month period with a suspected acute cerebrovascular event. We evaluated scan quality by using 2 different methods: First, we quantitatively assessed arterial opacification by measuring attenuation values in 9 arterial segments from the aortic arch to the distal cervical internal carotid artery, by using a threshold of 150 HU as an indicator of good opacification. Second, we assessed image contrast between arteries and veins by measuring attenuation within venous segments and recording the number of artery-vein-segment pairs in which the attenuation difference was <or=50 HU. In addition, we recorded the prevalence of the following artifacts: metallic hardware streak, contrast material streak from slow-flowing contrast material in adjacent large veins, streak artifacts from shoulders, contrast material reflux into veins of the neck, motion artifacts, and artifacts causing misrepresentation of flow dynamics simulating arterial dissection or occlusion. These results were compared with those of a historical control group of 113 patients from our institution who were imaged with the same technical parameters on a 16-section CT scanner.
RESULTS: The quantitative assessment of arterial opacification showed that 854 of 885 analyzed arterial segments (96.5%) had good opacification (ie, attenuation values >150 HU). Image contrast between artery and vein segments was also good, with 714 of 763 analyzable segment pairs (85.6%) having >50 HU difference. Artifacts obscuring arterial evaluation included streak from contrast material in the subclavian/brachiocephalic vein (32% of patients), attenuation of the x-ray beam between the shoulders (28%), beam-hardening from metallic hardware (26%), and contrast material reflux into neck veins (16%). The most clinically relevant artifacts were flow artifacts, mimicking dissection or vascular occlusion; they were seen in 14% of patients and likely are related to the rapid data acquisition for CTA on 64-section scanners (compared with the circulation of contrast material in the cervical arteries). None of the patients in our historical control group who underwent 16-section CT had flow artifacts on their CTA studies; the incidence of the other types of artifacts in this group was similar to that in patients imaged with 64-section CT.
CONCLUSIONS: The 64-section CTA imaging protocol for carotid arteries yields high-quality studies in >95% of cases.