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

Abstract

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.

In Vivo Mapping of the Chemical Exchange Relayed Nuclear Overhauser Effect using Deep Magnetic Resonance Fingerprinting (rNOE-MRF)

“…Several previous works were able to mitigate or eliminate the water T 1 , T 2 , and semisolid MT contributions from the rNOE signals 12,[14][15][16] . However, these approaches still require a lengthy full Zspectrum acquisition or are directly affected by the saturation pulse settings employed 2,17 , limiting the ability to compare image ndings across different sites. In any case, rNOE-weighted images represent a combined contribution from the aliphatic proton volume fraction and exchange rate, hindering the direct evaluation of the compound of interest concentration.…”

Early-stage mapping of macromolecular content in APPNL-F mouse model of Alzheimer’s disease using nuclear Overhauser effect MRI

“…Simple, yet informative, techniques for assessing metabolic, related to glucose and neurotransmitter metabolism, and macromolecular content, related to lipid and protein content, of brain tissue include chemical exchange saturation transfer (CEST) and nuclear Overhauser effect (NOE) MRI ( Van Zijl and Yadav, 2011 ; Jones et al, 2013 ; Benyard et al, 2023 ). A typical CEST experiment involves the saturation of exchangeable metabolite protons at a resonance frequency offset from that of water protons.…”