Carotid Artery Wall Imaging: Perspective and Guidelines from the ASNR Vessel Wall Imaging Study Group and Expert Consensus Recommendations of the American Society of Neuroradiology

Abstract

Identification of carotid artery atherosclerosis is conventionally based on measurements of luminal stenosis and surface irregularities using in vivo imaging techniques including sonography, CT and MR angiography, and digital subtraction angiography. However, histopathologic studies demonstrate considerable differences between plaques with identical degrees of stenosis and indicate that certain plaque features are associated with increased risk for ischemic events. The ability to look beyond the lumen using highly developed vessel wall imaging methods to identify plaque vulnerable to disruption has prompted an active debate as to whether a paradigm shift is needed to move away from relying on measurements of luminal stenosis for gauging the risk of ischemic injury. Further evaluation in randomized clinical trials will help to better define the exact role of plaque imaging in clinical decision-making. However, current carotid vessel wall imaging techniques can be informative. The goal of this article is to present the perspective of the ASNR Vessel Wall Imaging Study Group as it relates to the current status of arterial wall imaging in carotid artery disease.

Quantitative susceptibility mapping of carotid plaques using nonlinear total field inversion: Initial experience in patients with significant carotid stenosis

“…The carotid plaque MRI protocol was based on recent recommendations by the American Society of Neuroradiology Vessel Wall Imaging Study Group and consisted of 3D GRE TOF, 2D black‐blood fat‐suppressed T1w and T2w turbo spin echo, and 3D‐MPRAGE sequences for mcMRI as well as 3D multi‐echo GRE sequence for QSM with approximately 6‐cm longitudinal coverage of the carotid bifurcation. The pertinent imaging parameters were as follows: Axial T1w turbo spin echo: TR/TE = 885/9.4 ms, echo train length = 7, number of signal averages = 2, readout bandwidth (rBW) = 410 Hz/pixel, voxel size = 0.63 × 0.63 × 2 mm 3 , and scan time = 4:12 minutes; axial T2w turbo spin echo: TR/TE = 4770/58 ms, echo train length = 12, number of signal averages = 3, rBW = 410 Hz/pixel, voxel size = 0.63 × 0.63 × 2 mm 3 , and scan time = 6:21 minutes; coronal MPRAGE: TR/TE/TI = 840/3.4/500 ms, flip angle = 15°, rBW = 331 Hz/pixel, voxel size = 0.63 × 0.63 × 0.83 mm 3 , and scan time = 3:44 minutes; axial TOF: TR/TE = 20/3.6 ms, flip angle = 30°, rBW = 250 Hz/pixel, voxel size = 0.63 × 0.63 × 2 mm 3 , and scan time = 4:03 minutes; and axial QSM: TR/first TE/TE spacing = 21/2.9/4.7 ms, echo train length = 4, flip angle = 10°, number of signal averages = 2, rBW = 580 Hz/pixel, voxel size = 0.63 × 0.63 × 2 mm 3 , and scan time = 8:03 min.…”

CT and MR Imaging of Carotid Wall and Plaque

“…CT is a non-invasive and widely used technique that allows assessment of the atherosclerotic plaque burden and the degree of stenosis. [13][14][15][16][17] Modern CT scanners are able to perform detailed imaging of the carotid artery lumen and of the plaque. Visualization of the vessel lumen is achieved by performing a CTA which requires the injection of an iodinated contrast medium.…”

“…Because of its excellent spatial resolution, CT imaging is a promising tool for the quantification of the volume of the carotid plaque and its sub-components (fattymixed -calcified) and it is potentially able to detect IPH. 13,[18][19][20] In particular, the introduction of multi-energy 21 technology further increases the capabilities of CT in the detection and characterization of carotid atherosclerosis. Advantages of multi-energy CT compared with conventional CT include the ability to differentiate calcified plaque from iodinated contrast, while also facilitating bone subtraction.…”

“…Limitations of CT are mainly related to the radiation dose delivered to the patients and to the potential side effects of contrast materials. 13,22,23 In the last years, several papers have been published using positron emission tomography (PET)-CT which can identify various functional images. 24 For PET, the most commonly used tracer is 18F-fluoro-2-deoxy-D-glucose (18F-FDG).…”

“…The impact of plaque imaging is considered in the recently published guidelines and perspectives. In particular, the perspective and guidelines from the American Society of Neuroradiology vessel wall imaging study group and expert consensus recommendations of the American Society of Neuroradiology, released in February 2018, 13 focused on the technological implications and impact of the imaging technologies for the carotid plaque imaging. In this document it is suggested that for carotid artery imaging some technological thresholds are necessary, and in particular for the CT at least a 32-detector-row CT scanner whereas for the MR at least a 1.5T with carotid coil or a 3T system (with or without dedicated carotid coil); moreover in order to obtain the necessary level of information by using the MR a minimum set of sequences are needed and are described in the document.…”