Diagnosis of multiple sclerosis through the lens of ultra-high-field MRI

Abstract

The long-standing relationship between ultra-high-field (7 T) MRI and multiple sclerosis (MS) has brought new insights to our understanding of lesion evolution and its associated pathology. With the recent FDA approval of a commercially available scanner, 7 T MRI is finally entering the clinic with great expectations about its potential added value. By looking through the prism of MS diagnosis, this perspective article discusses current limitations and prospects of 7 T MRI techniques relevant to helping clinicians diagnose patients encountered in daily practice.

Keywords: Brain; Diagnosis; Magnetic Resonance Imaging; Multiple sclerosis; Ultra-high-field.

Published by Elsevier Inc.

Figures

Figure 1

Left: T2-weighted images acquired with 3D SPACE (TSE with variable flip angles) at 0.8 mm isotropic. Main sequence parameters: TE = 399 ms, TR = 8000 ms, R = 4 (GRAPPA), scan time = 6 min 20 sec. In addition to the image bias field coming from the receive B1- field (32-channel head coil used here), there are signal voids in the cerebellum on both contrasts due to poor homogeneity of the transmit B1+ field (yellow arrows). Right: T2-FLAIR images acquired using 3D SPACE with inversion recovery at 0.8 mm isotropic. Main sequence parameters: TI =2150 ms, TE = 399 ms, TR = 8000 ms, R = 4 (GRAPPA), scan time = 6 min 26 sec. Although CSF suppression is fairly homogenous across the brain on T2-FLAIR, tissue and lesion contrasts are reduced due to some T1 weighting effects coming from the elongated T1 values at 7 T.

Figure 2

Top: T1-weighted 3D MPRAGE acquired at 0.7 mm isotropic. Main sequence parameters: TI = 1050 ms, FA = 7 degrees, TE = 2.96 ms, TR = 2200 ms, R = 2 (GRAPPA), scan time = 6 min 35 sec. Bottom: T1-weighted 3D MP2RAGE acquired at 0.7 mm isotropic. Main sequence parameters: TI1 = 800 ms, TI2 = 2700 ms, FA = 4, 5 degrees, TE = 3 ms, TR = 6000 ms, R = 3 (GRAPPA), scan time = 10 min 3 sec. Both acquisitions are from the same MS patient. Compared to MPRAGE, MP2RAGE image is almost entirely free of image bias and allows detection of MS-related pathology in the pons and cerebellum (yellow arrows).

Figure 3

Top: T1-weighted 3D MP2RAGE before injection of GBCA. Bottom: T1-weighted 3D MP2RAGE acquired 5 minutes after injection of GBCA (single dose of gadobutrol). Both acquisitions are from the same MS patient and performed at 0.7 mm isotropic with the same sequence parameters: TI1 = 800 ms, TI2 = 2700 ms, FA = 4, 5 degrees, TE = 3 ms, TR = 6000 ms, R = 3 (GRAPPA), scan time = 10 min 3 sec.

Figure 4

T2*-weighted 2D gradient-echo sequences performed on two MS patients at 7 T using an in-plane resolution of 250 μm × 250 μm, a slice thickness of 1 mm, and 25 contiguous slices. Image on left (first MS patient) was acquired in an axial orientation and shows multiple white matter MS lesions with a central vein (arrows). Images on the right (second MS patient) were acquired in a coronal orientation, and minimum intensity projection was performed for the image on top. The ‘fan-shaped’ distribution of the deep medullary veins (top image, dashed boxes) and the oblique course of a vein running centrally through a MS lesion (bottom image, yellow arrow) are illustrated. Main sequence parameters were: FA = 50 degrees, TE = 20 ms, TR = 1300 ms, R = 2 (GRAPPA), scan time = 8 min 40 sec.

Figure 5

T2*w multi-shot EPI sequence performed on a MS patient at 7T using 0.5 mm isotropic voxels. Whole-brain coverage was achieved in less than 8 min. Multi-planar reconstruction allows visualization of a central vein within a deep white matter lesion (yellow arrows in magnified views). Main sequence parameters were: FA = 10, TE = 23 ms, TR = 52 ms, EPI factor = 15 (echo train length of ~ 26 ms). This multi-shot EPI acquisition provides a 15-fold acceleration compared to a GRE acquisition at similar resolution and TR.

Figure 6

Left: T2*-weighted 3D gradient-echo acquired at 0.5 mm isotropic. Main sequence parameters: FA = 70 degrees, TE = 33 ms, TR = 4095 ms, R = 2 (SENSE), 60 axial slices, scan time = 13 min 28 sec. Right: T1-weighted 3D MP2RAGE acquired at 0.5 mm isotropic. Main sequence parameters: TI1 = 1000 ms, TI2 = 2700 ms, FA = 4, 5 degrees, TE = 3 ms, TR = 6000 ms, R = 3 (GRAPPA), scan time = 10 min 32 sec. A small (intra) cortical lesion is depicted on both contrasts (yellows crossbars) in this MS patient.