Key clinical benefits of neuroimaging at 7T

Abstract

The growing interest in ultra-high field MRI, with more than 35.000 MR examinations already performed at 7T, is related to improved clinical results with regard to morphological as well as functional and metabolic capabilities. Since the signal-to-noise ratio increases with the field strength of the MR scanner, the most evident application at 7T is to gain higher spatial resolution in the brain compared to 3T. Of specific clinical interest for neuro applications is the cerebral cortex at 7T, for the detection of changes in cortical structure, like the visualization of cortical microinfarcts and cortical plaques in Multiple Sclerosis. In imaging of the hippocampus, even subfields of the internal hippocampal anatomy and pathology may be visualized with excellent spatial resolution. Using Susceptibility Weighted Imaging, the plaque-vessel relationship and iron accumulations in Multiple Sclerosis can be visualized, which may provide a prognostic factor of disease. Vascular imaging is a highly promising field for 7T which is dealt with in a separate dedicated article in this special issue. The static and dynamic blood oxygenation level-dependent contrast also increases with the field strength, which significantly improves the accuracy of pre-surgical evaluation of vital brain areas before tumor removal. Improvement in acquisition and hardware technology have also resulted in an increasing number of MR spectroscopic imaging studies in patients at 7T. More recent parallel imaging and short-TR acquisition approaches have overcome the limitations of scan time and spatial resolution, thereby allowing imaging matrix sizes of up to 128×128. The benefits of these acquisition approaches for investigation of brain tumors and Multiple Sclerosis have been shown recently. Together, these possibilities demonstrate the feasibility and advantages of conducting routine diagnostic imaging and clinical research at 7T.

Keywords: 7T; MRSI; clinical; fMRI; high resolution; neuroimaging.

Fig. 1

Sagittal 3D DIR of an MS patient acquired at 3 T (A) and 7 T (B). A cortical lesion - type I neocortical lesion (NL) (Yao et al., 2014) (leukocortical lesion, mixed lesion) (red arrow) - is more clearly depicted at 7 T.

Fig. 2

Axial SWI images of an MS patient acquired at 3 T (A) and 7 T (B) and corresponding T2-weighted images acquired at 3 T (C) and 7 T (D). Note iron deposits (rims) and central vessels within MS lesions in SWI images (A, B) (white arrows). In T2-weighted images central vessels are difficult to detect (C, D) (white arrows).

Fig. 3

Coronal T2-weighted images at 3 T (A) and 7 T (B) of a patient suffering from right-sided MTS type 1. Neuronal loss in all hippocampal subfields CA1, CA2, CA3, and CA4. Corresponding histopathological correlate, NeuN staining (C).

Fig. 4

Presurgical mapping of the primary hand motor representation in a patient with 2 oligo-dendrogliomas grade II (1 right frontal, 1 right central). Activation in primary motor, somatosensory and supplementary areas can be seen in fMRI results showing voxels which were activated with between 20% and 100% reliability (overlaid on the mean EPI). No smoothing or coregistration of the functional results was performed.

Fig. 5

Data acquired via an ultra-short TE MRSI sequence at 7 T in a 38-year-old male patient with an anaplastic oligoastrocytoma WHO grade III. In the left top, a T₁ weighted post-contrast image is shown. Sample maps of seven different brain metabolites are presented including total N-acetyl aspartate (tNAA), total choline (tCho), total creatine (tCr), glutamate (Glu), glutamine (Gln), myo-inositol (mIns), and sum of lipids (Lip). Note the increased tCho in the tumor border zone and contra-lateral side, decreased tNAA in the hemisphere containing the tumor, increased myo-inositol in the contralateral hemisphere, increased Glu and Gln in the tumor border zone, and increased lipids in the necrotic zone of the tumor.