Carotid Plaque Characterization Using 3D T1-Weighted MR Imaging with Histopathologic Validation: A Comparison with 2D Technique

BACKGROUND AND PURPOSE:3D FSE T1WI has recently been used for carotid plaque imaging, given the potential advantages in contrast and spatial resolutions. However, its diagnostic performance remains unclear. Hence, we compared the ability of this technique to readily assess plaque characteristics with that of conventional images and validated the results with histologic classification.MATERIALS AND METHODS:We prospectively examined 34 patients with carotid stenosis who underwent carotid endarterectomy by using 1.5T scanners and obtained 3D-FSE T1WI and 2D spin-echo T1WI scans. After generating reformatted images obtained from the 3D-FSE T1-weighted images, we calculated the contrast ratios for the plaques and the adjacent muscles and compared these findings with the pathologic classifications.RESULTS:Carotid plaques were histologically classified as types VII, VIII, IV–V, or VI. With 3D-FSE T1WI, the range of contrast ratios for each classification was the following: 0.94–0.97 (median, 0.95), 0.95–1.29 (median, 1.10), 1.33–1.54 (median, 1.42), and 1.53–2.12 (median, 1.80), respectively. With 2D imaging, the range of contrast ratios for each classification was the following: 0.79–1.02 (median, 0.90), 0.88–1.19 (median, 1.01), 1.17–1.46 (median, 1.23), and 1.55–2.51 (median, 2.07), respectively. Results were significantly different among the 4 groups (P < .001). Sensitivity and specificity for discriminating vulnerable plaques (IV–VI) from stable plaques (VII, VIII) were both 100% for the 3D technique and 100% and 91%, respectively, for the 2D technique.CONCLUSIONS:3D-FSE T1WI accurately characterizes intraplaque components of the carotid artery, with excellent sensitivity and specificity compared with those of 2D-T1WI.

Cervical carotid stenosis is an important cause of cerebral infarction and transient ischemic attack. Carotid endarterectomy or carotid artery stent placement is performed to prevent future stroke events but may also cause embolic complications during the surgery, especially if the plaque contains substantial vulnerable components such as intraplaque hemorrhage or lipid.^1,2 Therefore, establishing a method for characterizing intraplaque components is an important prerequisite for predicting perisurgical complications.Several modalities have been used for plaque characterization, including ultrasonography and MR imaging. Although ultrasonography is widely used, the interpretation is typically subjective and may be impossible in the presence of extensive calcification or a high-positioned carotid bifurcation. Although gray-scale median and integrated backscatter have been introduced as quantitative metrics, previous reports suggest that they are unsuitable for evaluating intraplaque components.^3,4 MR plaque imaging is another popular method for assessing plaque characteristics. Although various imaging techniques have been used, a 2D spin-echo (SE) T1WI technique with appropriate scanning parameters has been reported to accurately quantify intraplaque components, compared with other conventional techniques.^5–8 Recently, a 3D T1WI FSE technique has been adopted for this purpose because it can minimize partial volume effects and motion artifacts, as well as enhance black-blood effects, while maintaining T1WI contrast. However, whether the 3D-FSE technique can more accurately discriminate among intraplaque components than the more conventional techniques, such as 2D-SE T1WI, remains unknown. Hence, in the present study, we investigated whether the diagnostic accuracy of 3D-FSE T1WI, in terms of carotid plaque characterization, is comparable with that of 2D-SE T1WI, by using pathologic specimens excised from carotid endarterectomy as our validation standards.