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When more is less: Higher magnetic fields and their limited impact on signal-to-noise ratio per unit of acquisition time in unlocalized and single-voxel magnetic resonance spectroscopy

Guodong Weng1,2,3,* and Johannes Slotboom1,2,†

  • 1Institute for Diagnostic and Interventional Neuroradiology, Inselspital, University Hospital and University of Bern, Bern, Switzerland
  • 2Translational Imaging Center, sitem-insel, Bern, Switzerland
  • 3Department of Radiology & Biomedical Imaging, Yale University, New Haven, Connecticut, USA

  • *Contact author: guodong.weng@unibe.ch
  • †Contact author: johannes.slotboom@insel.ch
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Phys. Rev. Applied 24, 054066 – Published 21 November, 2025

DOI: https://doi.org/10.1103/j138-v9gr

Abstract

Magnetic resonance spectroscopy (MRS) offers significant diagnostic potential but is inherently constrained by a low signal-to-noise ratio (SNR). While increasing the main magnetic field strength B0 is theoretically linked to increased SNR, practically obtained gains in SNR from B07/4 to B0, depending on the domination of thermal noise at high B0, are not always realized. Especially in clinical settings, the maximum reachable SNR is further constrained by the total available acquisition time (TA) and the regulatory limits on maximum tolerable specific absorption rate (SAR). This work attempts to derive mathematical expressions that enable systematic analysis of the theoretically achievable SNR gain. One important notion in this context is the SNR gain per unit of measurement time as a function of the main magnetic field B0 strengths in the case of unlocalized X-nuclei and localized (1H and X-nuclei) single-voxel spectroscopy (SVS) pulse sequences. Our findings indicate that, under given fixed total amount of (patient acceptable) measurement time TA and maximum tolerable SAR limitation, together with conditions that ensure the adiabaticity of specific sequences, there exists an optimal magnetic field strength B0 that maximizes SNR per unit of measurement time (SNRt). Beyond this optimal B0, further increases in field strength do not yield proportional improvements in SNRt. Key factors are identified, including rf-pulse bandwidth scaling with B0 and longitudinal relaxation time (T1) dependencies, that impact the net gain as well. Our theoretical analysis emphasizes critical considerations for optimizing SNR per unit time in clinical MRS, even challenging the presumption that higher magnetic fields B0 always yield improved SNR per unit of measurement time performance.

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Phys. Rev. Applied 24, 054066– Published 21 November, 2025
  • Received 11 April 2025
  • Revised 7 August 2025
  • Accepted 29 August 2025
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

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