Magnetic Resonance Imaging Detection of Intraplaque Hemorrhage

Abstract

Carotid artery atherosclerosis is a major cause of ischemic stroke. For more than 30 years, future stroke risk and carotid stroke etiology have been determined using percent diameter stenosis based on clinical trials in the 1990s. In the past 10 years, magnetic resonance imaging (MRI) sequences have been developed to detect carotid intraplaque hemorrhage. By detecting carotid intraplaque hemorrhage, MRI identifies potential stroke sources that are often overlooked by lumen imaging. In addition, MRI can dramatically improve assessment of future stroke risk beyond lumen stenosis alone. In this review, we discuss the use of heavily T1-weighted MRI sequences used to detect carotid intraplaque hemorrhage. In addition, advances in ciné imaging, motion robust techniques, and specialized neck coils will be reviewed. Finally, the clinical use and future impact of MRI plaque hemorrhage imaging will be discussed.

Keywords: MRI; atherosclerosis; intraplaque hemorrhage; stroke.

Figure 1.

Intraplaque hemorrhage (IPH) detection and histology: (A) in vivo and (B) ex vivo 3-T magnetic resonance images of carotid plaque with T2-weighted, T1-weighted, and magnetization-prepared rapid acquisition gradient echo (MPRAGE) sequences from left to right. MPRAGE-positive plaque is outlined with a solid line, as defined using a 2-fold threshold compared with adjacent muscle. IPH and lipid/necrotic core were defined on histology with trichrome stain with (C) 1× and (D) 20× images. MPRAGE (+) signal corresponded to areas of IPH (solid line) as opposed to lipid/necrosis (dashed line). Hematoxylin-eosin and phosphotungstic acid hematoxylin stains were also used to confirm the presence of recent hemorrhage.

Figure 2.

Neck-shape–specific coils. (A) Standard neck coils with a large all-encompassing anterior neck coil are made to accommodate all patient shapes and sizes at the expense of poor signal-to-noise ratio (SNR). (B) The standard magnetic resonance imaging head/neck coil can be fitted with a 7-channel neck-shape–specific coil that fits close to the surface of the neck. This provides significantly higher SNR than the commercial coil alone.

Figure 3.

Full head/neck images with high signal-to-noise ratio (SNR) carotid coils: three-dimensional (3D) ciné-Retrospective Ordering and Compressed Sensing (ciné-ROCS), delay alternating with nutation for tailored excitation with fast low-angle shot (DASH) coronal images acquired with the standard magnetic resonance imaging (MRI) head/neck coil (A) without or (B) with the addition of 7-channel coils on the same volunteer. Imaging parameters for the 3D ciné-ROCS DASH image: isotropic voxel dimensions = 0.63 mm, repetition time/echo time = 2.5/8.0 ms, field of view = 240 × 240 mm, matrix size = 384 × 384 × 96, delay alternating with nutation for tailored excitation prep. = 150 ms, flip angle = 8.0°, and scan time = 8 minutes 20 seconds. SNR maps demonstrate 200- to 400-fold increased SNR comparing the standard MRI head/neck coil (C) without versus (D) with the 7-channel coils.

Figure 4.

Optimized magnetic resonance imaging-intraplaque hemorrhage imaging with magnetization-prepared rapid acquisition gradient echo (MPRAGE): comparison of (A) standard Cartesian MPRAGE (top = coronal, bottom = axial reformat) with (B) an optimized stack of stars MPRAGE sequence (top = coronal, bottom = axial reformat) demonstrates complete suppression of flow artifact and background tissue signal. This patient has bilateral carotid intraplaque hemorrhage centered at the bifurcations. Both sequences were acquired in the same patient with neck-shape–specific coils.