RESEARCH ARTICLE

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

Sophia Swago

orcid.org/0000-0001-8334-4746

Department of Bioengineering, School of Engineering and Applied Sciences, University of Pennsylvania, Philadelphia, Pennsylvania, USA

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Mark A. Elliott,

Mark A. Elliott

Department of Radiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA

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Ravi Prakash Reddy Nanga,

Ravi Prakash Reddy Nanga

orcid.org/0000-0002-3644-5656

Department of Radiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA

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Neil E. Wilson,

Neil E. Wilson

Department of Radiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA

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Abigail Cember,

Abigail Cember

Department of Radiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA

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Ravinder Reddy,

Ravinder Reddy

Department of Radiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA

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Walter R. Witschey,

Corresponding Author

Walter R. Witschey

[email protected]

orcid.org/0000-0003-1669-2120

Department of Radiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA

Correspondence

Walter Witschey, Department of Radiology, 3400 Civic Center Blvd., South Pavilion, Room 11-155, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA.

Email: [email protected]

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Sophia Swago,

Sophia Swago

orcid.org/0000-0001-8334-4746

Department of Bioengineering, School of Engineering and Applied Sciences, University of Pennsylvania, Philadelphia, Pennsylvania, USA

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Mark A. Elliott,

Mark A. Elliott

Department of Radiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA

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Ravi Prakash Reddy Nanga,

Ravi Prakash Reddy Nanga

orcid.org/0000-0002-3644-5656

Department of Radiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA

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Neil E. Wilson,

Neil E. Wilson

Department of Radiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA

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Abigail Cember,

Abigail Cember

Department of Radiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA

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Ravinder Reddy,

Ravinder Reddy

Department of Radiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA

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Walter R. Witschey,

Corresponding Author

Walter R. Witschey

[email protected]

orcid.org/0000-0003-1669-2120

Department of Radiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA

Correspondence

Walter Witschey, Department of Radiology, 3400 Civic Center Blvd., South Pavilion, Room 11-155, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA.

Email: [email protected]

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First published: 18 February 2023

https://doi.org/10.1002/mrm.29615

Citations: 2

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Funding information: National Heart, Lung, and Blood Institute, Grant/Award Numbers: F31 HL158217, R01 HL137984; National Institute of Biomedical Imaging and Bioengineering, Grant/Award Number: P41 EB029460

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Abstract

Purpose

The purpose of this study was to characterize the ¹H 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 ¹H resonances between 8.0 and 8.5 ppm in the healthy human calf muscle at 7 T.

Supporting Information

Filename

Description

mrm29615-sup-0001-Supinfo.docxWord 2007 document , 2.2 MB

Figure S1. The ¹H downfield region in a single subject after frequency-selective excitation (E-BURP 90° pulse centered at 9.0 ppm with bandwidth (BW) = 2 ppm, voxels = 40 × 40 × 40 mm, TR/TE = 7 s/20 ms), without water suppression (left), and with VAPOR (variable pulse power and optimized relaxation delays) water suppression showing attenuated metabolite peaks (right)

Figure S2. Antisymmetric water sidebands are visible (solid arrows) in the ¹H spectrum of a water phantom (top row) and in vivo (bottom row) with frequency-selective excitation (E-BURP 90° pulse with BW = 2 ppm, voxels = 40 × 40 × 40 mm, TR/TE = 1 s/20 ms) centered at 4.7 ppm on water (left column). Sidebands are not visible in the same frequency locations (dashed arrows) when the same sequence is applied with excitation centered at 9.0 ppm (right column, zoomed × 140) in either the phantom (top row) or in vivo (bottom row)

Figure S3. Recovery of magnetization and three-parameter fits for all subjects (n = 7) using broadband and selective inversion-recovery (IR) data. Both selective and broadband data for each subject were normalized to the magnetization of the subject's last selective TI (2500 ms) for each resonance

Figure S4. Percent error between estimated T₁ and true T₁ in 1000 simulated selective IR data sets, plotted against selective inversion efficiency k (k = 0 indicating no inversion, k = 1 indicating perfect inversion). The maximum error across the three resonances is < 16%. The average percent error was 2.01 ± 1.56%, 1.79 ± 1.40%, and 2.12 ± 2.00% for the 8.0, 8.2, and 8.5 ppm peaks, respectively

Figure S5. Percent error between estimated cross-relaxation rate σ_AB and true σ_AB of 1000 simulated data sets plotted against selective (k_sel) and broadband (k_broad) inversion efficiencies (k = 0 indicating no inversion, k = 1 indicating perfect inversion). The maximum error across the three resonances is < 16%. The average percent error was 2.18 ± 1.68%, 2.23 ± 1.77%, and 2.45 ± 1.95% for the 8.0, 8.2, and 8.5 ppm peaks respectively

Table S1. Empirically determined constraints [min, max] for the component frequencies, line widths, and phases used to assign Hankel singular value decomposition (HSVD) components

Note: The 8.2-ppm and 8.5-ppm peaks were always assigned one component, and the 8.0-ppm component was assigned between one and three components.

Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

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Citing Literature

Volume90, Issue1

July 2023

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Ultra-High Field MR

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

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