Ultrahigh-Resolution Imaging of the Human Brain with Phase-Cycled Balanced Steady-State Free Precession at 7 T

Abstract

Objective To acquire ultra-high resolution images of the brain using balanced steady-state free precession (bSSFP) at 7.0T and to identify the potential utility of this sequence. Materials and Methods 8 subjects participated in this study after providing informed consent. Each subject was scanned with 8 phase-cycles of bSSFP at 0.4mm isotropic resolution using 0.5 NEX and two-dimensional parallel acceleration of 1.75 × 1.75. Each phase cycle required 5 minutes of scanning, with pauses between the phase cycles allowing short periods of rest. The individual phase cycles were aligned and then averaged. The same subjects underwent scanning using 3D multi-echo GRE at 0.8mm isotropic resolution, 3D CUBE T2 at 0.7mm isotropic resolution, and thin-section coronal oblique T2-weighted FSE at 0.22 × 0.22 × 2.0 mm resolution for comparison. Two neuroradiologists assessed image quality and potential research and clinical utility. Results Subjects generally tolerated the scan sessions well, and composite high-resolution bSSFP images were produced for each subject. Rater analysis demonstrated that bSSFP had superior 3D visualization of the microarchitecture of the hippocampus, very good contrast to delineate the borders of the subthalamic nucleus, and relatively good B1 homogeneity throughout. In addition to excellent visualization of the cerebellum, subtle details of brain and skull base anatomy were also easier to identify on the bSSFP images, including the line of Gennari, membrane of Lillequist, and cranial nerves. bSSFP had a strong iron contrast similar to or better than the comparison sequences. However, cortical gray-white contrast was significantly better with CUBE T2 and T2-weighted FSE. Conclusions bSSFP can facilitate ultra-high resolution imaging of the brain. While total imaging times are long, the individually short phase-cycles can be acquired separately, improving exam tolerability. These images may be beneficial for studies of the hippocampus, iron-containing structures such as the subthalamic nucleus and line of Gennari, and the basal cisterns and their contents.

Gastric Carcinoma: Ex Vivo MR Imaging at 7.0 T–Correlation with Histopathologic Findings

“…MR imaging at 7.0 T recently has been introduced Implication for Patient Care n MR imaging at 7.0 T may provide a powerful tool with which to noninvasively visualize the depth of mural invasion by gastric carcinomas. as a means of acquiring high-spatialresolution MR images of the brain and intracranial diseases (19,20). To our knowledge, however, there have been no reports of using high-spatial-resolution 7.0-T MR imaging to evaluate the depth of mural invasion by gastric carcinomas.…”

“…MR imaging at 7.0 T yields the highest field strength that is currently available in clinical MR systems (19,20). Since the signal-to-noise ratio increases almost linearly with field strength, 7.0-T MR imaging systems offer the flexibility to use a higher intrinsic signal-tonoise ratio than standard-field-strength systems.…”

“…The acquisition time was 102 minutes for the T2-weighted images and 20 minutes for the T1-weighted images. We chose an effective echo time of 80 msec for the T2-weighted images because the previous study used an effective echo time of 47 or 83 msec for T2-weighted images of the brain at 7.0 T (19) and because T2 value changes are very pronounced at 7.0 T (20). We also TECHNICAL DEVELOPMENTS: Gastric Carcinoma Yamada et al considered that a longer effective echo time might reduce the signal-to-noise ratio considerably.…”

Ultra-high resolution in-vivo 7.0 T structural imaging of the human hippocampus reveals the endfolial pathway

“…Studying the hippocampus at high-resolution in-vivo may lead to better imaging biomarkers and improve diagnostic accuracy (Kerchner, 2011; Kerchner et al, 2010; Yushkevich et al, 2009). We have recently shown that at 7.0 T, balanced steady state free precession (bSSFP) demonstrates high signal-to-noise ratio and produces a superior depiction of the MTL (Zeineh et al, 2014). In this study we have used the bSSFP sequence at 7.0 T to further investigate the ultra-structure of the hippocampus, and have found that we can reliably identify the EF pathway in vivo .…”

Magnetic Resonance Imaging and Computed Tomography of the Brain—50 Years of Innovation, With a Focus on the Future

“…3). [37][38][39][40] As with other specific techniques such as susceptibility weighted imaging, 39 time of flight magnetic resonance angiography at ultrahigh field should be markedly superior to that at 3 T. Advances in TOF imaging technique are ongoing, with amelioration of SAR constraints enabling venous suppression, 41 improving excitation fidelity, leading to higher contrast, and achieving smooth slab transitions. 42 Carotid imaging at 7 T has attracted substantial attention, given the importance of spatial resolution in evaluating the carotid wall and atherosclerotic disease.…”