Improvements in carotid plaque imaging using a new eight‐element phased array coil at 3T

Carotid Atherosclerosis is a leading cause of stroke-related morbidity and mortality due to rupture of atherosclerotic plaques formed near the carotid bifurcation. Plaque size and composition are known to be important determinants of plaque vulnerability (1–3). Noninvasive evaluation of plaque morphology and composition by imaging techniques is desirable to predict vulnerable plaques. High-resolution magnetic resonance imaging (MRI) of the carotid vessel wall can accurately measure lesion size and comprehensively assess plaque composition (4,5) and thereby assess plaque vulnerability. Multicontrast carotid MRI can identify vulnerable plaque components such as the presence of a large necrotic core (6–8), thin or ruptured fibrous cap (8,9), intraplaque hemorrhage (10,11), and has been shown to predict patient symptoms (12,13). Carotid MRI is increasingly used to monitor lesion progression and regression in response to antiatherosclerotic therapies (14,15). Higher spatial resolution MRI is required to identify the small changes in plaque morphology and composition typical of short drug trials. Maintaining good signal-to-noise ratio (SNR) at a high spatial resolution within a clinically acceptable scan time is crucial for measuring small plaque components. Phased-array (PA) surface coils specifically designed for carotid imaging have been shown to provide improved SNR at the carotid bifurcation (16–18). These studies have demonstrated the superiority of PA coils and identified favorable coil element geometries. Availability of clinical 3T scanners and newer black-blood multicontrast pulse sequences optimized for imaging at 3T provide improved SNR over 1.5 T (19). However, limited experience with PA coils for carotid imaging is available at 3 T (20). Current coil designs have shortcomings for use in large-scale clinical trials and prospective epidemiologic studies of carotid atherosclerosis. The location of the carotid bifurcation varies significantly from patient to patient, and from side to side within the same patient. Thus, larger anatomical coverage along the length of the artery is needed to avoid coil repositioning. Additionally, in large subjects with thicker necks the carotid arteries are deep and located away from the surface. Coil sensitivity at these depths is an important design consideration for studies involving such subjects. With the development of faster scanning techniques and improvements in 3D carotid vessel wall imaging (21–23), longer segments of the artery can be assessed by increasing coil coverage along the length of the artery. Additionally, longitudinal coverage of up to 5 cm of the carotids is desirable for assessment of plaque away from the bifurcation and for maintaining lesion coverage in serial studies. Thus, a dedicated carotid coil optimized to improve both SNR and coverage of the carotid bifurcation, is required to enable high-resolution imaging for use in clinical studies at 3T. A high SNR four-element PA (4PA) coil for carotid imaging has been previously demonstrated at 1.5T (16). In this study a new coil of similar design with eight elements (8PA) is compared against the 4PA design at 3T in terms of coverage, SNR, and contrast-to-noise ratio (CNR).