Intraplaque characteristics assessed by preoperative 2D magnetic resonance (MR) carotid plaque imaging may be associated with development of microembolic signals (MES) ¹ during carotid dissection in carotid endarterectomy (CEA). On the other hand, it is unclear what position of the plaque, especially at the position showing maximum stenosis or maximum signal intensity, is deeply associated with development of MES, however, it is difficult to validate it by 2D plaque imaging. The aim of the present study was to determine what position of the plaque signal intensity identified by preoperative 3D fast spin echo (3D-FSE) T1-weighted (T1W) plaque imaging² in carotid artery stenosis is deeply associated with development of MES on transcranial Doppler (TCD) during exposure procedure of the carotid arteries in CEA.Sixty patients with intracranial artery (ICA) stenosis (≧70%) underwent preoperative sagittal 3D-FSE T1WI of the affected carotid bifurcation within 1 week prior to CEA using a 1.5T MR imaging scanner (Signa HDxt; GE Healthcare, Milwaukee, Wisconsin) and an 8-channel neurovascular coil. The pulse sequence parameters were as follows: flow-sensitized 3D-FSE with variable flip angles; TR/TE, 500/18.3 ms; echo-train length, 24; b-value of the flow-sensitized gradients along 3 axes, 2.2 s/mm²; FOV, 25 × 19 cm²; matrix size, 512 × 512 (after zero-fill interpolation); section interval, 0.5 mm (after zero- fill interpolation); partitions, 248; voxel size, 0.5 × 0.5 × 0.5 mm³; parallel imaging factor, 2; NEX, 1; fat suppression, chemical shift selective suppression; and acquisition time, 3 minutes 54 seconds. Motion-sensitized gradients of 2.2 s/mm² were used as the black-blood technique. Data of 3D-FSE T1W plaque imaging were processed by using a free software package (OsiriX, Pixmeo, Geneva, Switzerland) as follows (Fig.1): curved planar reformation (CPR) image was automatically generated along the carotid artery by carefully placing reference points in the center of the vessel on each axial source image. And then, new axial images perpendicular to the center line, connecting reference points in the center of the vessel, were reformatted with 1.0 mm thickness. In each patient, a reformatted axial image with the maximal plaque size and that with maximal plaque intensity were identified. In these two images, contrast ratio (CR) of the carotid plaque was calculated by dividing plaque signal intensity by sternocleidomastoid muscle signal intensity. Then CEA under TCD monitoring of MES in the ipsilateral middle cerebral artery (MCA). TCD was performed using a PIONEER TC2020 system (EME, Uberlingen, Germany; software version 2.50, 2-MHz probe; diameter, 1.5 cm; insonation depth, 40-66 mm; scale, -100 and +150 cm/s; sample volume, 2 mm; 64-point fast Fourier transform; fast Fourier transform length, 2 mm, fast Fourier transform overlap, 60%; high-pass filter, 100 Hz; detection threshold, 9 dB; minimum increase time, 10 ms) for insonation of the MCA ipsilateral to the carotid artery undergoing CEA. TCD data were stored on a hard disk using a coding system and were later analyzed manually by a clinical neurophysiologist who was blinded to patient information. MES were identified during exposure of the carotid arteries (from skin incision until ICA clamping).CR_{max_size} and CR_{max_intensity} were significantly higher in 16 patients with MES than in 44 patients without MES (p<0.0001). For all patients, the area under the receiver operating characteristic curve (AUC) to discriminate between presence and absence of MES was significantly greater with CR_{max_intensity} (0.929) than with CR_{max_size} (0.879) (p=0.0246). For 27 patients with identification of the image with the maximal plaque size and that with the maximal plaque intensity, AUCs for CR_{max_size} and CR_{max_intensity} were 1.000. For 33 patients without this identification, the AUC was significantly greater for CR_{max_intensity} (0.866) than for CR_{max_size} (0.787) (p=0.0110).Consequently, preoperative 3D-FSE T1W plaque imaging for cervical carotid artery stenosis could demonstrate the deference in the ability for development of MES on TCD during exposure procedure of the carotid arteries in CEA between the highest signal intensity in the plaque and the signal intensity at the position with showing the highest degree of stenosis. It may be important for assessment for the plaque vulnerability in cervical carotid artery stenosis to carefully choose the position to measure the signal intensity of the plaque, not only the position with showing the maximum stenosis but also that with showing the highest signal intensity.