Feasibility of transient nuclear Overhauser effect imaging in brain at 7 T

Abstract

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.

B1+$$ {\mathrm{B}}_1^{+} $$ inhomogeneity correction of volumetric brain NOEMTR via high permittivity dielectric padding at 7 T

“…Therefore, multifaceted correction techniques that combine postprocessing and pad usage and, even in the future, pTx, and artificial intelligence should be considered. Consideration should also be given to using dielectric pads and other methods to correct for the same $$$ {\mathrm{B}}_1^{+} $$$ inhomogeneities present in similar sequences at 7 T such as creatine CEST 33 and transient NOE 34 …”

Personalized and muscle-specific OXPHOS measurement with integrated CrCEST MRI and proton MR spectroscopy

“…One contained deionized water and the other contained 100 mM creatine in DPBS, each had a pH of 7.05 and were scanned at room temperature. The same parameters were used as in previous work 27 .…”

In vivo reproducibility of 3D relayed NOE in the healthy human brain at 7 T

“…Patients with high-grade tumors (World Health Organization grade IV) have shown to have reduced rNOE signals in the tumor region due to a degradation of protein content in the brain. 7 Recently, another study has shown the feasibility of measuring transient NOE from the lipids of human brains in vivo at 7 T. 29 Mehrabian et al 30 and Regnery et al 31 demonstrated that rNOE can characterize tumor aggressiveness and identify early progressors even before beginning the treatment. Regnery et al 31 and Meissner et al 32 showed that rNOE-CEST can be used as a biomarker to predict early progression after therapy of CRT in glioblastoma, discriminating between responders and nonresponders.…”