Seven-Tesla magnetic resonance imaging: new vision of microvascular abnormalities in multiple sclerosis

Abstract

Background: Although the role of vascular pathology in multiple sclerosis (MS) lesions was suggested long ago, the derivation of these lesions from the vasculature has been difficult to assess in vivo. Ultrahigh-field (eg, 7-T) magnetic resonance imaging (MRI) has become a tool for assessing vascular involvement in MS lesions owing to markedly increased image resolution and susceptibility contrast of venous blood.

Objective: To describe the perivenous association of MS lesions on high-resolution and high-contrast 7-T susceptibility-sensitive MRI.

Design: Case study.

Setting: University hospital.

Patients: Two women with clinically definite relapsing-remitting MS.

Results: We demonstrated markedly enhanced detection of unique microvascular involvement associated with most of the visualized MS lesions with abnormal signals on and around the venous wall on 7-T compared with 3-T MRI.

Conclusions: These findings, which have never been shown on conventional fields of MRI, not only allow for direct evidence of vascular pathogenesis in MS in vivo but also have important implications for monitoring lesion activity and therapeutic response.

Figure 1. 7T high resolution axial T2*-weighted images in Patient 1

Two representative images at the levels of the lateral ventricles (A) and centrum semiovale (B) depict centrally-coursing veins in a context of various vascular abnormalities associated with MS lesions. These abnormalities include small lesions with clearly distinguishable central veins (white arrows), small lesions with hazy-appearing and indistinct central veins (green arrows), large lesions with well-defined central veins (yellow arrows), and large lesions with ill-defined central veins (red arrows). These different presentations may indicate different stages of lesion development and associated levels of vascular involvement.

Figure 2. T2*-weighted images at the level of the basal ganglia on 7T MRI in Normal Control (A) and Patient 1 (B) as well as on 3T MRI in Patient 1 (C)

The lesions (yellow arrows) in close proximity to the optic radiations (white arrowheads), as depicted, seem to follow a perivenous distribution and not that of the dense white matter fiber tracts. Compared to normal control, there is marked increased iron deposition in the basal ganglia and thalamic areas (white arrows). Also shown is a cortical lesion originating from the cortical sulcus (red arrows). Furthermore, the perivenous relationship of lesions and cortical lesion is poorly demonstrated on 3T compared to 7T MRI with the similar sequence acquisitions.

Figure 3. High resolution axial T2*-weighted images in Patient 1 at baseline (A) and follow up over nine months (B) on 7T as well as enhanced T1-weighted image (C) on 3T

An example of one small lesion with abnormal perivascular signal (arrow) demonstrates an increased size of lesion and increased signal of central venous structure on the same 7T T2*-weighted images acquired 9 months later. On Gd-enhanced scans on 3T, no contrast enhancement is noted associated this lesion with increased size.

Figure 4. 7T high resolution axial T2*-weighted images in Patient 2

Four representative images at different levels also demonstrate a variety of vascular abnormalities associated with MS lesions.