Ultra-high field MR imaging lacks B 1 + inhomogeneity due to shorter RF wavelengths used at higher field strengths compared to human anatomy.CEST techniques tend to be highly susceptible to B 1 + inhomogeneities due to a high and uniform B 1 + field being necessary to create the endogenous contrast.High-permittivity dielectric pads have seen increasing usage in MR imaging due to their ability to tailor the spatial distribution of the B 1 + field produced. The purpose of this work is to demonstrate that dielectric materials can be used to improve glutamate weighted CEST (gluCEST) at 7T. Theory and Methods:GluCEST images were acquired on a 7T system on six healthy volunteers. Aqueous calcium titanate pads, with a permittivity of approximately 110, were placed on either side in the subject ′ s head near the temporal lobes. A post-processing correction algorithm was implemented in combination with dielectric padding to compare contrast improvement. Tissue segmentation was performed to assess the effect of dielectric pads on gray and white matter separately. Results: GluCEST images demonstrated contrast enhancement in the lateral temporal lobe regions with dielectric pad placement. Tissue segmentation analysis showed an increase in correction effectiveness within the gray matter tissue compared to white matter tissue. Statistical testing suggested a significant difference in gluCEST contrast when pads were used and showed a difference in the gray matter tissue segment. Conclusion:The use of dielectric pads improved the B 1 + field homogeneity and enhanced gluCEST contrast for all subjects when compared to data that did not incorporate padding.

Purpose Nuclear Overhauser effect (NOE) is based on dipolar cross‐relaxation mechanism that enables the indirect detection of aliphatic protons via the water proton signal. This work focuses on determining the reproducibility of NOE magnetization transfer ratio (NOEMTR) and isolated or relayed NOE (rNOE) contributions to the NOE MRI of the healthy human brain at 7 Tesla (T). Methods We optimized the B1+$$ {\mathrm{B}}_1^{+} $$ amplitude and length of the saturation pulse by acquiring NOE images with different B1+$$ {\mathrm{B}}_1^{+} $$ values with multiple saturation lengths. Repeated NOE MRI measurements were made on five healthy volunteers by using optimized saturation pulse parameters including correction of B0 and B1+$$ {\mathrm{B}}_1^{+} $$ inhomogeneities. To isolate the individual contributions from z‐spectra, we have fit the NOE z‐spectra using multiple Lorentzians and calculated the total contribution from each pool contributing to the overall NOEMTR contrast. Results We found that a saturation amplitude of 0.72 μT and a length of 3 s provided the highest contrast. We found that the mean NOEMTR value in gray matter (GM) was 26%, and in white matter (WM) was 33.3% across the 3D slab of the brain. The mean rNOE contributions from GM and WM values were 8.9% and 9.6%, which were ∼10% of the corresponding total NOEMTR signal. The intersubject coefficient of variations (CoVs) of NOEMTR from GM and WM were 4.5% and 6.5%, respectively, whereas the CoVs of rNOE were 4.8% and 5.6%, respectively. The intrasubject CoVs of the NOEMTR range was 2.1%–4.2%, and rNOE range was 2.9%–10.5%. Conclusion This work has demonstrated an excellent reproducibility of both inter‐ and intrasubject NOEMTR and rNOE metrics in healthy human brains at 7 T.

The nuclear Overhauser effect (NOE) quantification from the steady-state NOE imaging suffers from multiple confounding non-NOE-specific sources, including direct saturation, magnetization transfer, and relevant chemical exchange species, and is affected by B 0 and B 1 + inhomogeneities. The B 0 -dependent and B 1 + -dependent data needed for deconvolving these confounding effects would increase the scan time substantially, leading to other issues such as patient tolerability. Here, we demonstrate the feasibility of brain lipid mapping using an easily implementable transient NOE (tNOE) approach.Methods: This 7T study used a frequency-selective inversion pulse at a range of frequency offsets between 1.0 and 5.0 parts per million (ppm) and −5.0 and −1.0 ppm relative to bulk water peak. This was followed by a fixed/variable mixing time and then a single-shot 2D turbo FLASH readout. The feasibility of tNOE measurements is demonstrated on bovine serum albumin phantoms and healthy human brains. Results:The tNOE measurements from bovine serum albumin phantoms were found to be independent of physiological pH variations. Both bovine serum albumin phantoms and human brains showed broad tNOE contributions centered at approximately −3.5 ppm relative to water peak, with presumably aliphatic moieties in lipids and proteins being the dominant contributors. Less prominent tNOE contributions of approximately +2.5 ppm relative to water, presumably from aromatic moieties, were also detected. These aromatic signals were free from any CEST signals. Conclusion:In this study, we have demonstrated the feasibility of tNOE in human brain at 7 T. This method is more scan-time efficient than steady-state NOE and provides NOE measurement with minimal confounders.

Nuclear Overhauser Effect (NOE) is an emerging technique to study mobile macromolecules such as lipids in the gray (GM) and white matter (WM) of the brain. In this work, we optimized the saturation pulse parameters of NOE Magnetization Transfer Ratio (MTR) MRI and investigated its reproducibility on a healthy human volunteer at 7 Telsa. We found that NOE-MTR of GM and WM regions of the brain was highly reproducible (COV<10%) over a three year time span. In addition, a saturation length of 3 to 4 sec provided optimal NOE-MTR contrast from both GM and WM regions of the brain.

In order to probe the metabolism of glutamate and myo-inositol for better understanding of the Alzheimer’s diseases (AD) we have employed the chemical exchange saturation transfer of glutamate (GluCEST) and myoinositol (MICEST) in a fast progressing, 5xFAD mouse model. There were significant differences observed in the GluCEST and MICEST maps of 5XFAD mice when compared to the wild-type (WT) mice for regions of interest drawn on hippocampus and thalamus, which are further supported by the spectroscopy results.