Intravascular magnetic resonance imaging of aortic atherosclerotic plaque composition

Magnetic resonance imaging (MRI) may be an excellent tool to define atherosclerotic plaque composition, but surface MRI (SMRI) suffers from a low signal-to-noise ratio and low resolution of arterial images. Intravascular MRI (IVMRI) represents a potential solution for acquiring high-quality in vivo images of atherosclerotic plaques. Isolated segments of 11 thoracic human aortas obtained at autopsy were imaged by IVMRI using an intravascular receiver catheter coil designed and built at our institution. Images obtained by IVMRI were compared with corresponding images obtained by SMRI and with histopathological aortic cross sections. The intensity of intimal thickness and plaque components was graded by IVMRI and histopathology using a score of 1 for mild 2 for moderate, and 3 for severe intensity. IVMRI had an agreement of 75% with histopathology in fibrous cap grading (37.5% expected, kappa=0.60, P<0.001) and of 74% in necrotic core grading (39% expected, kappa=0.57, P<0.001). Intraplaque calcification was correctly graded by IVMRI in six of the eight plaques in which histopathology recognized calcium. The analysis of intimal thickness showed 80% agreement between IVMRI and histopathology (52% expected, kappa=0.59, P<0.001). IVMRI image features were similar to those of SMRI. In addition, NMRI accurately determined atherosclerotic plaque size in comparison with histopathology and SMRI (slope=1.25 cm(2), r=0.99, P<0.001 for luminal area by IVMRI vs histopathology; slope=0.97 cm(2), r=0.996, P<0.001 for luminal area by IVMRI vs SMRI). IVMRI has the potential to provide important prognostic information in patients with atherosclerosis because of its ability to accurately assess both plaque composition and size.