# Neurochemical Profiles of Prefrontal Cortex and Hypothalamus at 3 and 7 T During Controlled Euglycemia: Evaluation in a Cohort With Type 1 Diabetes

## TL;DR

This study compares brain metabolite levels measured at 3 T and 7 T MRI in people with Type 1 diabetes, finding consistent overall profiles but some systematic differences.

## Contribution

The study is the first to compare MRS data at 3 T and 7 T in a clinical cohort under controlled glycemic conditions.

## Key findings

- Neurochemical profiles were highly similar between 3 T and 7 T, but some metabolites showed systematic differences.
- Using creatine ratios did not reduce biases and increased significant differences in metabolite quantifications.
- Strong correlations between 3 T and 7 T measurements suggest detectable inter-individual differences in neurochemical levels.

## Abstract

With the increasing adoption of ultrahigh‐field MRI scanners, there is a growing interest in migrating MRS studies from 3 to 7 T. Prior field comparisons of MRS in healthy volunteers demonstrated better reliability of quantification at 7 T, particularly for weakly represented metabolites. Neurochemical quantification has not been compared at 3 T versus 7 T in clinical cohorts and under controlled physiological conditions. In this exploratory study, we analyzed MRS data from the hypothalamus and prefrontal cortex volumes of interest (VOIs) that were collected from the same individuals with Type 1 diabetes at 3 and 7 T as a part of a larger study investigating cerebral responses to glycemic changes. Seventeen individuals underwent MRS during euglycemic clamps at both 3 T and 7 T, allowing us to compare metabolite concentrations obtained at the two fields with a consensus‐recommended short‐echo semi‐LASER protocol under the same physiological conditions. Our aim was to examine whether there are systematic biases in neurochemical concentrations measured at 3 T versus 7 T and to assess whether creatine (tCr) ratios would reduce or eliminate such biases. High‐quality spectra were obtained from both VOIs and fields, with 8–15 reliably quantified (mean Cramér–Rao lower bounds ≤ 20%) metabolites from LCModel. Whereas neurochemical profiles were highly similar between 3 and 7 T, several metabolites exhibited systematic differences with water‐referenced quantifications, such as glucose + taurine (Glc + Tau) and phosphoethanolamine. Quantifications with tCr as reference did not alleviate the biases and, in fact, resulted in a larger number of significant differences due to systematic biases in the tCr concentration. Pearson correlation analysis showed significant associations for several metabolites between 3 and 7 T, suggesting that interindividual differences in neurochemical levels are detectable. Associations were stronger when using tCr ratios. Importantly, hypothalamic Glc + Tau showed a strong correlation between fields at these tightly regulated euglycemic conditions, opening the possibility to detect individualized glucose concentrations in this brain region that participates in the regulation of blood glucose levels.

This study compares MRS data acquired at 3 T and 7 T from the hypothalamus and prefrontal cortex in individuals with Type 1 diabetes. Despite similar metabolite levels, systematic differences were observed, particularly in phosphoethanolamine and the sum of glucose and taurine. Using creatine ratios did not eliminate and, in fact, exacerbated these biases. Significant correlations between concentration estimates at 3 T and 7 T suggest that inter‐individual differences in select neurochemical levels are detectable over a narrow range of blood glucose levels.