Cerebrospinal fluid–suppressed T₂‐weighted MR imaging at 7 T for human brain

Abstract

Purpose T 2 ‐weighted lesional imaging is most commonly performed using inversion recovery turbo spin echoes. At 7 T, however, this acquisition is limited for specific absorption rate and resolution. This work describes and implements a method to generate CSF‐suppressed T 2 ‐weighted imaging. Methods The strategy uses a driven equilibrium spin‐echo preparation within an inversion recovery with multiple 3D gradient‐echo imaging blocks. Images are combined using the self‐normalization approach, which achieves CSF suppression through optimized timing of individual blocks and minimizes sources of variation due to coil receptivity, T 2 * , and proton density. Simulations of the magnetization‐prepared fluid‐attenuated inversion recovery gradient‐echo (MPFLAGRE) method over T 1 and T 2 relaxation values are performed, and in vivo demonstrations using an 8 2 transceiver array in healthy controls are shown. Results The specific absorption rate of the calculated MPFLAGRE sequence is 11.1 ± 0.5 W (n = 5 volunteers), which is 74 ± 2% of the US Food and Drug Administration guidelines. This method acquires both contrasts for CSF suppression with detection of long T 2 components and T 2 ‐weighted imaging in a single acquisition. In healthy controls, the former contrast generates increased signal in the cortical rim and ependyma. A comparison is shown with a conventional 3D SPACE fluid‐attenuated inversion recovery acquisition, and sensitivity to pathology is demonstrated in an epilepsy patient. Conclusion As applied with the 8 2 transceiver, the MPFLAGRE sequence generates both whole‐brain contrast suitable for lesional and T 2 ‐weighted imaging at 7 T in fewer than 10 minutes within the US Food and Drug Administration's specific absorption rate guidelines.

7T Epilepsy Task Force Consensus Recommendations on the Use of 7T MRI in Clinical Practice

“…As a consequence, finding the balance between signal intensities across the brain may be subject to radiologic priorities, that is, whether a radiologist wants to focus on medial (prioritize low FA) or lateral (prioritize high FA) structures. These difficulties have led to research into new types of RF pulse strategies and sequence designs 24,25 to mitigate these problems.…”

The Role of Advanced Imaging in Neurosurgical Diagnosis

“…Other pathologies of a vascular nature, such as cerebral hemorrhage, thrombosed aneurysm, arteriovenous malformation, cavernoma, and microhemorrhage, are also seen in T2-weighted images [14] . Unfortunately, T2 is limited by the signal produced by CSF with partial volume effects and flow artifacts which significantly inhibit periventricular and subcortical brain region 4/14 https://www.doi.org/10.53964/jmmi.2023002 evaluation [15] . Within the spine, T2-weighted imaging is helpful in the detection and diagnosis of stenosis, nerve root compression, disc disease, or infection [16] .…”

“…Cerebrovascular disease: Cerebral blood flow in reversible cerebral ischemia has been investigated using 15 O-H 2 O PET and perfusion-weighted imaging (PWI) [68] . Adoption of PWI methods, including DSC and ASL, is still lacking for regular clinical usage due to the lack of consistency and unpredictability in the values the techniques produce.…”

“…The best imaging method for studying cerebral vascular perfusion continues to be PET and MRI [69] . However, because it is difficult to provide a radiotracer with a brief half-life in the right amount of time to examine brain hemodynamics during an acute stroke, the practical use of 15 O-H 2 O PET in stroke remains a challenge.…”

Clinical 7T MRI for epilepsy care: Value, patient selection, technical issues, and outlook

“…While FDA approved 2D and 3D FLAIR T2WI sequences modified to stay within SAR, spatial and temporal limitations are available at 7T, the T2‐weighting is generally poor compared to 3 or 1.5T 2 . Innovative approaches currently in research/development that have been reported to improve T2WI and FLAIR‐T2WI include novel pulse sequences, such as gradient and spin echo, simultaneous multislice with power independent of number of slices, magnetization‐prepared fluid‐attenuated inversion recovery gradient‐echo approaches, 3D tailored RF pulses, and synthetic MR with deep learning reconstruction , 2,38,39 but to date, none are available as FDA‐approved sequences. For now, the use of 7T as the final tier in our multitier imaging strategy reduces the impact of this issue, because a combination of comparison 1.5T or 3T FLAIR T2WI images and 7T T2WI is generally sufficient to evaluate for transmantle sign and hippocampal edema/gliosis.…”