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Carotid Plaque Morphology and Composition: Initial Comparison between 1.5- and 3.0-T Magnetic Field Strengths¹

¹ From the Departments of Radiology (H.R.U., V.L.Y., J.W., N.B., C.E.H., M.O., W.Y., D.X., B.C., C.Y.) and Surgery (T.S.H.), University of Washington, 815 Mercer St, Box 358050, Seattle, WA 98109; Pfizer, Groton, Conn (B.T.W.); and Mountain-Whisper-Light Statistical Consulting, Seattle, Wash (N.L.P.). Received June 25, 2007; revision requested August 23; revision received October 11; accepted December 19; final version accepted January 31, 2008. Supported by Pfizer and the National Institutes of Health (R01 HL61851, P01 HL072262, R01 HL073401, T-32 HL07838). Address correspondence to C.Y.(e-mail: cyuan{at}u.washington.edu).

Purpose: To prospectively compare the interpretation and quantification of carotid vessel wall morphology and plaque composition at 1.5-T with those at 3.0-T magnetic resonance (MR) imaging.

Materials and Methods: Twenty participants (mean age, 69.8 years [standard deviation] ± 10.5; 75% men) with 16%–79% carotid stenosis at duplex ultrasonography were imaged with 1.5-T and 3.0-T MR imaging units with bilateral four-element phased-array surface coils. This HIPAA-compliant study was approved by the institutional review board, and all participants gave written informed consent. Protocols designed for similar signal-to-noise ratios across platforms were implemented to acquire axial T1-weighted, T2-weighted, intermediate-weighted, time-of-flight, and contrast material–enhanced T1-weighted images. Lumen area, wall area, total vessel area, wall thickness, and presence or absence and area of plaque components were documented. Continuous variables from different field strengths were compared by using the intraclass correlation coefficient (ICC) and repeated measures analysis. The Cohen was used to evaluate agreement between 1.5 T and 3.0 T on compositional dichotomous variables.

Results: There was a strong level of agreement between field strengths for all morphologic variables, with ICCs ranging from 0.88 to 0.96. Agreement in the identification of presence or absence of plaque components was very good for calcification ( = 0.72), lipid-rich necrotic core ( = 0.73), and hemorrhage ( = 0.66). However, the visualization of hemorrhage was greater at 1.5 T than at 3.0 T (14.7% vs 7.8%, P < .001). Calcifications measured significantly (P = .03) larger at 3.0 T, while lipid-rich necrotic cores without hemorrhage were similar between field strengths (P = .9).

Conclusion: At higher field strengths, the increased susceptibility of calcification and paramagnetic ferric iron in hemorrhage may alter quantification and/or detection. Nevertheless, imaging criteria at 1.5 T for carotid vessel wall interpretation are applicable at 3.0 T.

© RSNA, 2008