MR imaging of the vessel wall

Abstract

Since the risks for thrombosis are more dependent on plaque composition than on the degree of luminal narrowing, the radiological assessment of atherosclerosis should extend beyond mere depiction of the arterial lumen. High-resolution MRI of the vessel wall can provide important information about the individual makeup of atherosclerotic plaques, potentially enabling early detection and characterization of lesions before narrowing of the vessel lumen occurs. The MR-based assessment of the vessel wall with sufficient spatial resolution and image contrast, however, remains challenging. Requirements include high signal-to-noise ratio, high contrast-to-noise ratio, good signal penetration depth and homogeneous signal throughout the vessel under investigation, as well as imaging protocols encompassing various contrast weightings. Numerous dedicated radiofrequency (RF) coils have been developed to achieve these goals employing either external surface phased-array coils, or alternatively, utilizing intravascular coils to image the vessel wall from inside the vessel and thus being invasive. For the non-invasive approach of imaging with surface coils, the carotid and the right coronary arteries have been favoured since they are of critical importance and since they are relatively superficial structures, accessible from the outside. To detect the early development of plaque and visualize it globally rather than locally, intravascular contrast agents on the basis of ultrasmall particles of iron oxide can be used as a marker of macrophage activity within the plaque. In the long run, it appears likely that the combination of luminal MR angiography with the administration of susceptibility-based contrast agents and subsequent high-resolution MR of detected atherosclerotic lesions with dedicated RF coils could evolve as the diagnostic concept of choice for the assessment of atherosclerotic disease.

Characterization of Carotid Atherosclerosis and Detection of Soft Plaque with Use of Black-Blood MR Imaging

“…Along with recent advances in imaging devices and techniques, many studies have documented the usefulness of high-resolution MR imaging in the diagnosis of plaque. [14][15][16][17][18][19][20][21] In addition to sorting plaque composition on the basis of MR signal intensity, if soft plaque can be differentiated from nonsoft plaque by overall plaque MR signal intensity, MR imaging will be a simple, objective, and useful method to diagnose carotid atherosclerosis. To our knowledge, however, few studies have closely assessed the MR imaging signals of plaque components by comparing CEA specimens with carotid MR imaging in vivo, 22 and the findings on MR imaging of carotid soft plaque have not been described.…”

Quadrature coil design for high‐resolution carotid artery imaging scores better than a dual phased‐array coil design with the same volume coverage

“…Plaque imaging and composition assessment at high resolution in the carotid arteries demands a high SNR and, therefore, optimal coil/signal reception (2,4,5,9,10). Previous studies demonstrated that phased-array coils provide better SNR than single-loop surface coils (6,11,12).…”

“…MRI HAS THE POTENTIAL to define atherosclerotic plaque components in vivo at the carotid artery (1)(2)(3)(4)(5)(6). Normally, the atherosclerotic plaque in the carotid artery has an averaged length of 2.0 -2.5 cm and the thickness in the axial plane is 5-10 mm.…”

“…In a previous study we compared a 3-inch single-loop coil with a phased-array coil and demonstrated that a more than 100% increase in SNR can be achieved at a depth of 3 cm at the center of the coil for the phased-array configuration (1)(2)(3)(4)(5)(6).…”

MR coil sensitivity inhomogeneity correction for plaque characterization in carotid arteries

“…Magnetic resonance imaging (MRI) can be used to diagnose and stage blood vessel disease by identifying lumen narrowing in a stenosis, by measuring blood flow, and by imaging plaque in the arterial wall 1 . We are focusing on the latter application in a comprehensive program that includes new imaging technologies such as intravascular coils, high field MRI, imaging agents, and advanced computer image analysis.…”