Henry, Pierre‐Gilles

PurposeAdvanced MRS protocols improve data quality and reproducibility relative to vendor‐provided protocols; however, they are challenging to incorporate into the clinical workflow and require local MRS expertise for successful implementation. Here, we developed an automated advanced MRS acquisition protocol at 3T to facilitate acquisition of high‐quality spectroscopic data without local MRS expertise.MethodsFirst, a B0 shimming protocol was selected for automation by comparing 3 widely used B0 algorithms (2 vendor protocols and FAST(EST)MAP). Next, voxel‐based B0 and B1 calibrations were incorporated into the consensus‐recommended semi‐LASER sequence and combined with an automated VOI prescription tool, a recently developed method for automated voxel prescription. The efficiency of collecting single‐voxel data from a clinical cohort (N = 40) with the automated protocol (calibration time and fraction of usable datasets) was compared with the nonautomated semi‐LASER protocol (N = 35) whereby all prescan calibrations were executed manually in the academic hospital setting with rotating MR technologists in the neuroradiology unit.ResultsA multi‐iteration FAST(EST)MAP protocol resulted in narrower water linewidths than vendor’s B0 shim protocols for data acquired from 6 brain locations (p < 1e‐5) and was selected for automation. The automated B0 and B1 calibrations resulted in a time saving of ~4.5 minutes per voxel relative to the same advanced protocol executed manually. All spectra acquired with the automated protocol were usable, whereas only 86% of those collected with the manual protocol were usable and spectral quality was more variable.ConclusionThe plug‐and‐play advanced MRS protocol allows automated acquisition of high‐quality MRS data with high success rate and consistency on a clinical 3T platform.

In vivo MRS is a non‐invasive measurement technique used not only in humans, but also in animal models using high‐field magnets. MRS enables the measurement of metabolite concentrations as well as metabolic rates and their modifications in healthy animals and disease models. Such data open the way to a deeper understanding of the underlying biochemistry, related disturbances and mechanisms taking place during or prior to symptoms and tissue changes. In this work, we focus on the main preclinical 1H, 31P and 13C MRS approaches to study brain metabolism in rodent models, with the aim of providing general experts’ consensus recommendations (animal models, anesthesia, data acquisition protocols). An overview of the main practical differences in preclinical compared with clinical MRS studies is presented, as well as the additional biochemical information that can be obtained in animal models in terms of metabolite concentrations and metabolic flux measurements. The properties of high‐field preclinical MRS and the technical limitations are also described.

Currently no definitive biomarker of Alzheimer's disease (AD) is available, and this impedes both clinical diagnosis in humans and drug discovery in transgenic animal models. Proton magnetic resonance spectroscopy ( 1 H MRS) provides a noninvasive way to investigate in vivo neurochemical abnormalities. Each observable metabolite can potentially provide information about unique in vivo pathological processes at the molecular or cellular level. In this study, the age-dependent 1 H MRS profile of transgenic AD mice was compared to that of wild-type mice. Twenty-seven APP-PS1 mice (which coexpress mutated human presenilin 1 and amyloid-β precursor protein) and 30 wild-type mice age 66-904 days were examined, some repeatedly. A reduction in the levels of N -acetylaspartate and glutamate, compared with total creatine levels, was found in APP-PS1 mice with advancing age. The most striking finding was a dramatic increase in the concentration of myo -inositol with age in APP-PS1 mice, which was not observed in wild-type mice. The age-dependent neurochemical changes observed in APP-PS1 mice agree with results obtained from in vivo human MRS studies. Among the different transgenic mouse models of AD that have been studied with 1 H MRS, APP-PS1 mice seem to best match the neurochemical profile exhibited in human AD. 1 H MRS could serve as a sensitive in vivo surrogate indicator of therapeutic efficacy in trials of agents designed to reduce neurotoxicity due to microglial activation. Because of its noninvasive and repeatable nature, MRS in transgenic models of AD could substantially accelerate drug discovery for this disease.