Comparison between 2D and 3D high-resolution black-blood techniques for carotid artery wall imaging in clinically significant atherosclerosis

High-resolution mri provides information about both gross morphology and tissue composition of the carotid atherosclerotic plaque (1,2). Measurements of plaque burden from black-blood MRI are widely used in clinical trials (1–3) to serially monitor response to therapy and/or disease progression. Plaque composition has also been shown to be an important indicator of plaque vulnerability and a possible endpoint in clinical studies (1–4). Detection of small plaque components (such as necrotic core, thrombus, and calcification) and their segmentation require high-resolution in all three dimensions. However, current protocols (1,2,5) for carotid imaging are typically based on two-dimensional (2D) black-blood sequences with low spatial resolution in the slice-select direction as compared to in-plane resolution (2–3 mm vs. 0.5–0.6 mm). In such a situation, reliable detection and reproducible measurements of plaque components are difficult due to the partial volume effect (4), and the gross morphological measurements in serial studies are prone to errors caused by variations in the slice position and alignment (6). Three-dimensional (3D) black-blood imaging can provide increased resolution in the slice-select direction with an increased signal-to-noise (SNR) ratio, and therefore may be advantageous in carotid MRI. Improved slice resolution would also provide the opportunity to register images in serial studies, and thus minimize slice-positioning errors. While the advantages of 3D acquisition have been demonstrated in black-blood angiography of relatively small vascular structures, such as brain vasculature (7,8) and coronary arteries (9,10), the experience in 3D black-blood vessel wall imaging of carotid arteries is limited (11–13). Common problems in 3D black-blood carotid artery imaging are time-consuming acquisition and less effective flow suppression. To decrease scan time, 3D turbo spin-echo (TSE) (11) and gradient and spin-echo (GraSE) (12) black-blood techniques have been applied with reduced field-of-view (FOV) acquisition by using either an inner volume imaging technique (11) or 2D spatial-selective excitation (12). While such methods require specialized pulse sequences that are not widely available, a regular 3D fast spin-echo (FSE) sequence with a relatively short TR can be used for carotid artery imaging with an acceptable scan time (13). To reduce flow sensitivity, 3D sequences have been equipped with the double inversion-recovery (DIR) preparation (9,11–13). In addition, the thickness of the imaged slab was shown to be important for achieving good flow suppression (13). With potential benefits of 3D acquisition, there is a clear interest in using this approach in serial clinical studies. However, quantitative clinical applications of 3D black-blood imaging require establishing compatibility between morphological measurements obtained using more traditional 2D and newer 3D techniques. The goal of this study was to compare morphological measurements of the carotid artery and atherosclerotic plaque between a 3D high-resolution black-blood imaging technique with a two-fold improvement in slice resolution based on a previously described design (13) and a 2D technique of similar coverage.