Quantification of cross-relaxation in downfield 1 H MRS at 7 T in human calf muscle

Sophia Swago; Mark A Elliott; Ravi Prakash Reddy Nanga; Neil E Wilson; Abigail Cember; Ravinder Reddy; Walter R Witschey

doi:10.1002/mrm.29615

Quantification of cross-relaxation in downfield ¹ H MRS at 7 T in human calf muscle

Magn Reson Med. 2023 Jul;90(1):11-20. doi: 10.1002/mrm.29615. Epub 2023 Feb 18.

Authors

Sophia Swago¹, Mark A Elliott², Ravi Prakash Reddy Nanga², Neil E Wilson², Abigail Cember², Ravinder Reddy², Walter R Witschey²

Affiliations

¹ Department of Bioengineering, School of Engineering and Applied Sciences, University of Pennsylvania, Philadelphia, Pennsylvania, USA.
² Department of Radiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA.

PMID: 36807934
PMCID: PMC10149600 (available on 2024-07-01)
DOI: 10.1002/mrm.29615

Abstract

Purpose: The purpose of this study was to characterize the ¹ H downfield MR spectrum from 8.0 to 10.0 ppm of human skeletal muscle at 7 T and determine the T₁ and cross-relaxation rates of observed resonances.

Methods: We performed downfield MRS in the calf muscle of 7 healthy volunteers. Single-voxel downfield MRS was collected using alternately selective or broadband inversion-recovery sequences and spectrally selective 90° E-BURP RF pulse excitation centered at 9.0 ppm with bandwidth = 600 Hz (2.0 ppm). MRS was collected using TIs of 50-2500 ms. We modeled recovery of the longitudinal magnetization of three observable resonances using two models: (1) a three-parameter model accounting for the apparent T₁ recovery and (2) a Solomon model explicitly including cross-relaxation effects.

Results: Three resonances were observed in human calf muscle at 7 T at 8.0, 8.2, and 8.5 ppm. We found broadband (broad) and selective (sel) inversion recovery T₁ = mean ± SD (ms): T_{1-broad,8.0ppm} = 2108.2 ± 664.5, T_1-sel,8.0ppm = 753.6 ± 141.0 (p = 0.003); T_{1-broad,8.2ppm} = 2033.5 ± 338.4, T_1-sel,8.2ppm = 135.3 ± 35.3 (p < 0.0001); and T_{1-broad,8.5ppm} = 1395.4 ± 75.4, T_1-sel,8.5ppm = 107.1 ± 40.0 (p < 0.0001). Using the Solomon model, we found T₁ = mean ± SD (ms): T_1-8.0ppm = 1595.6 ± 491.1, T_1-8.2ppm = 1737.2 ± 963.7, and T_1-8.5ppm = 849.8 ± 282.0 (p = 0.04). Post hoc tests corrected for multiple comparisons showed no significant difference in T₁ between peaks. The cross-relaxation rate σ_AB = mean ± SD (Hz) of each peak was σ_AB,8.0ppm = 0.76 ± 0.20, σ_AB,8.2ppm = 5.31 ± 2.27, and σ_AB,8.5ppm = 7.90 ± 2.74 (p < 0.0001); post hoc t-tests revealed the cross-relaxation rate of the 8.0 ppm peak was significantly slower than the peaks at 8.2 ppm (p = 0.0018) and 8.5 ppm (p = 0.0005).

Conclusion: We found significant differences in effective T₁ and cross-relaxation rates of ¹ H resonances between 8.0 and 8.5 ppm in the healthy human calf muscle at 7 T.

Keywords: T1 relaxation time; cross-relaxation; downfield spectroscopy; magnetic resonance spectroscopy; skeletal muscle; spectral excitation.

Quantification of cross-relaxation in downfield ¹ H MRS at 7 T in human calf muscle

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