High resolution 7T MR imaging in characterizing culprit intracranial atherosclerotic plaques

Abstract

Background: Current imaging modalities underestimate the severity of intracranial atherosclerotic disease (ICAD). High resolution vessel wall imaging (HR-VWI) MRI is a powerful tool in characterizing plaques. We aim to show that HR-VWI MRI is more accurate at detecting and characterizing intracranial plaques compared to digital subtraction angiography (DSA), time-of-flight (TOF) MRA, and computed tomography angiogram (CTA).

Methods: Patients with symptomatic ICAD prospectively underwent 7T HR-VWI. We calculated: degree of stenosis, plaque burden (PB), and remodeling index (RI). The sensitivity of detecting a culprit plaque for each modality as well as the correlations between different variables were analyzed. Interobserver agreement on the determination of a culprit plaque on every imaging modality was evaluated.

Results: A total of 44 patients underwent HR-VWI. Thirty-four patients had CTA, 18 TOF-MRA, and 18 DSA. The sensitivity of plaque detection was 88% for DSA, 78% for TOF-MRA, and 76% for CTA. There's significant positive correlation between PB and degree of stenosis on HR-VWI MRI (p < 0.001), but not between PB and degree of stenosis in DSA (p = 0.168), TOF-MRA (p = 0.144), and CTA (p = 0.253). RI had a significant negative correlation with degree of stenosis on HR-VWI MRI (p = 0.003), but not on DSA (p = 0.783), TOF-MRA (p = 0.405), or CTA (p = 0.751). The best inter-rater agreement for culprit plaque detection was with HR-VWI (p = 0.001).

Conclusions: The degree of stenosis measured by intra-luminal techniques does not fully reflect the true extent of ICAD. HR-VWI is a more accurate tool in characterizing atherosclerotic plaques and may be the default imaging modality in clinical practice.

Keywords: 7T; culprit plaques; high-resolution vessel wall imaging; intracranial atherosclerosis; plaque burden.

Figure 1.

Plaque analysis based on 2D diameters measurements and ROIs. This figure is copyrighted to Edgar Samaniego and published with permission.

Figure 2.

Culprit plaque identification for every image modality. High-resolution vessel wall imaging (HR-VWI) is considered the gold standard.

Figure 3.

A patient with a history of vertebro-basilar insufficiency symptoms presented with a cerebellar infarct. The measurement of the vertebral artery (VA) culprit plaque on all modalities is illustrated: upper row shows measurement of the stenotic segment and lower row of the normal proximal parent artery segment. A ROI is delineated at the level of the plaque (A, upper row) and the normal vessel (A, lower row) in orthogonal planes. The degree of stenosis (DS) is determined by ROIs = 78.1% (A) and diameter measurements = 68.6% (B). DS vary significantly (78 to 40%) based on the imaging modality used: DSA (C) = 67.7%, TOF MRA (D) = 54.3%, and CTA (E) = 40%. In this example the plaque has circumferential positive remodeling which directly translates into luminal stenosis. In the DSA (C), the plaque appears to occupy only one side of the VA, but on HR-VWI the plaque extends along the entire arterial segment.