Comparison of 2D and multislab 3D magnetic resonance techniques for measuring carotid wall volumes

Abstract

Purpose: To compare a multislab three-dimensional volume-selective fast spin-echo (FSE) magnetic resonance (MR) sequence with a routine two-dimensional FSE sequence for quantification of carotid wall volume. Materials and Methods:One hundred normal subjects (50 men, mean age 44.6 years) underwent carotid vessel wall MR using 2D and 3D techniques. Carotid artery total vessel volume, lumen volume, wall volume, and wall/outer wall (W/OW) ratio were measured over 20 contiguous slices. Two-(2D) and three-dimensional (3D) results were compared. Results:The mean difference between 2D and 3D datasets (as a percentage of the mean absolute value) was 1.7% for vessel volume, 4.9% for lumen volume, 4.7% for wall volume, and 5.8% for W/OW ratio. There was good correlation between 2D and 3D models for total vessel volume (R 2 ϭ 0.93, P Ͻ 0.001), lumen area (R 2 ϭ 0.92, P Ͻ 0.001), and wall volume (R 2 ϭ 0.77, P Ͻ 0.001). The correlation for the W/OW ratio was weaker (R 2 ϭ 0.30; P Ͻ 0.001). The signalto-noise ratio (SNR) for the 3D technique was 2.1-fold greater than for the 2D technique (P Ͻ 0.001). When using the 3D sequence, scan time was reduced by 63%. Conclusion:Multislab volume selective 3D FSE carotid arterial wall imaging performs similarly to a conventional 2D technique, but with over twice the SNR and substantially reduced scan time. CARDIOVASCULAR MAGNETIC RESONANCE (MR) is a good technique for assessing atherosclerosis in the carotid artery, with much development over the last 15 years in plaque characterization and assessment of the structure and function of the arterial wall (1-6). Quantitative carotid wall imaging typically requires a stack of two-dimensional (2D) images, which can be contoured and analyzed. Acquisition protocols vary, but scan times of the order of 1 hour are common so as to cover an adequate length of the carotid artery with contiguous slices. Long scan times limit the applicability of the technique. As scan times increase, patient comfort and acceptability decrease, and patient movement increases, leading to image degradation from movement artifact (7). Long scan times also limit the feasibility of using carotid MR in large clinical studies. To reduce the scan time, a localized three-dimensional (3D) fast spinecho (FSE) sequence for carotid artery imaging has been developed and validated (8 -13).In conventional 3D imaging, rather than a single slice, a slab of tissue is excited by the radiofrequency (RF) pulse. Spatial encoding is performed in 3D by using additional phase encoding in the direction perpendicular to the selected slab, along with an additional dimension of Fourier transformation for image reconstruction (14). The 3D images have an inherently higher signal-to-noise ratio (SNR), so fewer cardiac cycles are needed than with 2D to produce similar image quality at the same voxel size (8,15). In theory, the SNR advantage of 3D over 2D is ͌N, where N is the number of 3D phase-encode steps in the partition direction. Using perpendicular 90°and 180°selection gradients, the 3D slab can ...

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