Seven‐Tesla Magnetization Transfer Imaging to Detect Multiple Sclerosis White Matter Lesions

Abstract

BACKGROUND AND PURPOSE: Fluid-attenuated inversion recovery (FLAIR) imaging at 3 Tesla (T) field strength is the most sensitive modality for detecting white matter lesions in multiple sclerosis. While 7T FLAIR is effective in detecting cortical lesions, it has not been fully optimized for visualization of white matter lesions and thus has not been used for delineating lesions in quantitative magnetic resonance imaging (MRI) studies of the normal appearing white matter in multiple sclerosis. Therefore, we aimed to evaluate the sensitivity of 7T magnetization-transfer-weighted (MT w ) images in the detection of white matter lesions compared with 3T-FLAIR. METHODS:Fifteen patients with clinically isolated syndrome, 6 with multiple sclerosis, and 10 healthy participants were scanned with 7T 3-dimensional (D) MT w and 3T-2D-FLAIR sequences on the same day. White matter lesions visible on either sequence were delineated. RESULTS: Of 662 lesions identified on 3T-2D-FLAIR images, 652 were detected on 7T-3D-MT w images (sensitivity, 98%; 95% confidence interval, 97% to 99%). The Spearman correlation coefficient between lesion loads estimated by the two sequences was .910. The intrarater and interrater reliability for 7T-3D-MT w images was good with an intraclass correlation coefficient (ICC) of 98.4% and 81.8%, which is similar to that for 3T-2D-FLAIR images (ICC 96.1% and 96.7%). CONCLUSION: Seven-Tesla MT w sequences detected most of the white matter lesions identified by FLAIR at 3T. This suggests that 7T-MT w imaging is a robust alternative for detecting demyelinating lesions in addition to 3T-FLAIR. Future studies need to compare the roles of optimized 7T-FLAIR and of 7T-MT w imaging.

Reduced Myelin Signal in Normal-appearing White Matter in Neuromyelitis Optica Measured by 7T Magnetic Resonance Imaging

“…Second, lesion detection was performed using MT sat (MTR based on proton- and T2*-weighted imaging with presaturation to water) images, which might not be as accurate as 3T fluid-attenuated inversion recovery (FLAIR) images. However, we previously showed that 7T-MT sat sequences detected most of the WM lesions identified by 3T-FLAIR sequences, and missed only approximately 1.5% of small lesions 34 ; hence, patients do not need to undergo both 7T and 3T scans on the same day. Third, the temporal lobes were not all included because the signal loss caused by inhomogeneity in the applied transmit radiofrequency (RF) field at high field strength was more pronounced in these regions.…”

Selective Inversion Recovery Quantitative Magnetization Transfer Brain MRI at 7T: Clinical and Postmortem Validation in Multiple Sclerosis

“…The latter protons do not directly contribute to the observed MRI signal in conventional sequences because of their short transverse relaxation times. The MT ratio (MTR) is a semi‐quantitative measure of the MT effect that can be estimated from an MT‐weighted and reference image . Studies indicate that MTRs change with myelin and axonal content, indicative of the degree of neurodegeneration.…”

“…The MT ratio (MTR) is a semiquantitative measure of the MT effect that can be estimated from an MT-weighted and reference image. 10,11 Studies indicate that MTRs change with myelin and axonal content, 12,13 indicative of the degree of neurodegeneration. In addition, MTR is sensitive to inflammation and edema.…”

MRI with ultrahigh field strength and high-performance gradients: challenges and opportunities for clinical neuroimaging at 7 T and beyond

“…The contribution of 7-T MRI for detecting MS white matter lesions is less robust than that for the cortex [ 43 ] with ongoing research in the optimization of sequences to reduce limitations secondary to high SAR and to reduce RF field inhomogeneities [ 43 – 45 ]. T2*, FLAIR, magnetization transfer imaging, and magnetization-prepared rapid gradient-echo have been suggested as currently recommended sequences to visualize white matter lesions at 7 T [ 43 , 46 , 47 ].…”