Diagnostic value of magnetic resonance imaging in carotid atherosclerotic disease

PURPOSE: İmaging methods used for diagnosing carotid disease can show the degree of stenosis but are inefficient at evaluating the vessel wall and composition of the atheroma plaque. Magnetic Resonance Imaging (MRI) has excellent contrast resolution and ability to distinguish between fibrotic, hemorrhagic and calcific components. The aim of our study is to diagnose symtomatic and asymtomatic plaque morphology with pathologic specimens after carotid endartectomy; to investigate whether or not the plaque components are identified with MRI and to find out the MRI characteristics of the plaque components in case that they are identified.METHODS: 37 patients who were scheduled for carotid endarterectomy for carotid stenosis (24 symtomatic, 13 asymptomatic) were imaged at 1.5 T Philips İntera Achieva MR system equipped with a surface coil (Philips Sense Flex Medium IPX4). The carotid bifurcation was centered around a five-centimeter-segment of the artery imaged. All patients underwent MR imaging within a week before surgery. Axial T1, T2, proton weighted images were performed for black blood imaging while 3D TOF MR angiography for bright blood imaging. Data were collected from electrocardiogram gated images. Black blood double inversion recovery technique with T1 and presaturation pulses with T2 and proton weighted images were used to reduce luminal signal.Plaque tissue components such as lipid-rich necrotic core (NC), hemorrhage, calcification, luminal trombus were identified by using previously published MR imaging criteria. All signal intensities were compared with the sternocleidomastoid muscle at a point adjecent to and at the same depth as the carotid arteries. All necrotic core diamensions measured at two axises. The fibrous caps were categorized as thinner or thicker than 0.5 mm. Two patients were excluded from the study becase of poor image quality.Thirtythree patients underwent carotid endarterectomy surgery. Plaque components, inflammatory cell infiltration and smooth muscle cells were searched at histological examination.RESULTS: Of the 33 patients all had necrotic core at histology sections and 30 of them were seen at MR imaging. There was no significant difference in necrotic core area measured between symtomatic and asymptomatic patients.The NC areas measured by MRI and histology were 9.17 ± 8.92 and 11.06 ± 10.68 respectively.Of the 33 patients, 30 showed calcification by MRI imaging and histology and there was no difference between the symtomatic and asymtomatic group.The senstivity of MRI to show hemorrhage was % 82.3 and the specificity was % 68.75 . meaning that MRI can be used to identify hemorrhagic areas of the plaque but there was no difference between the symtomatic and asymtomatic group.Smooth muscle cells were found much more frequently in asymtomatic patiens and macrophage cells were were in turn more frequently encountered in symtomatic ones.Fibrous cap (FC) thickness measuments by histology showed that patiens without symptoms had thicker FCs than the symtomatic ones but there was no significant statistical difference.Necrotic core signals were best shown at T2 weighted and hemorrhage signal at T1 and T2 weighted imagesCONCLUSIONS: Invivo MRI is capable of identifying NC, FC, hemorrhage and calcification at atheroma plaque. The statistical performance of our study was poorer than we thought becose of the fewer number of asymptomatic patients. Our experience of atheroma plaques with this study will be usefull for imaging large patient series without the need for histologic corelation.