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Improved free-breathing liver fat and iron quantification using a 2D chemical shift–encoded MRI with flip angle modulation and motion-corrected averaging

Abstract

Objectives

3D chemical shift–encoded (CSE) MRI enables accurate and precise quantification of proton density fat fraction (PDFF) and R2*, biomarkers of hepatic fat and iron deposition. Unfortunately, 3D CSE-MRI requires reliable breath-holding. Free-breathing 2D CSE-MRI with sequential radiofrequency excitation is a motion-robust alternative but suffers from low signal-to-noise-ratio (SNR). To overcome this limitation, this work explores the combination of flip angle–modulated (FAM) 2D CSE imaging with a non-local means (NLM) motion-corrected averaging technique.

Methods

In this prospective study, 35 healthy subjects (27 children/8 adults) were imaged on a 3T MRI-system. Multi-echo 3D CSE (“3D”) and 2D CSE FAM (“FAM”) images were acquired during breath-hold and free-breathing, respectively, to obtain PDFF and R2* maps of the liver. Multi-repetition FAM was postprocessed with direct averaging (DA)– and NLM-based averaging and compared to 3D CSE using Bland-Altmann and regression analysis. Image qualities of PDFF and R2* maps were reviewed by two radiologists using a Likert-like scale (score 1–5, 5 = best).

Results

Compared to 3D CSE, multi-repetition FAM-NLM showed excellent agreement (regression slope = 1.0, R2 = 0.996) for PDFF and good agreement (regression slope 1.08–1.15, R2 ≥ 0.899) for R2*. Further, multi-repetition FAM-NLM PDFF and R2* maps had fewer artifacts (score 3.8 vs. 3.2, p < 0.0001 for PDFF; score 3.2 vs. 2.6, p < 0.001 for R2*) and better overall image quality (score 4.0 vs. 3.5, p < 0.0001 for PDFF; score 3.4 vs. 2.7, p < 0.0001 for R2*).

Conclusions

Free-breathing FAM-NLM provides superior image quality of the liver compared to the conventional breath-hold 3D CSE-MRI, while minimizing bias for PDFF and R2* quantification.

Key Points

2D CSE FAM-NLM is a free-breathing method for liver fat and iron quantification and viable alternative for patients unable to hold their breath.

2D CSE FAM-NLM is a feasible alternative to breath-hold 3D CSE methods, with low bias in proton density fat fraction (PDFF) and no clinically significant bias in R2*.

Quantitatively, multiple repetitions in 2D CSE FAM-NLM lead to improved SNR.

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Abbreviations

CSE:

Chemical shift–encoded

DA:

Direct averaging

FAM:

Flip angle modulation

NLM:

Non-local means

PDFF:

Proton density fat fraction

REP:

Repetition

SNR:

Signal-to-noise ratio

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Acknowledgements

The authors thank David T Harris, PhD, for his assistance with the organization and recruitment.

Funding

The authors wish to acknowledge support from GE Healthcare and Bracco Diagnostics who provide research support to the University of Wisconsin, and support from the NIH (K24 DK102595, R01 DK088925, R01 DK100651, R44-EB025729, R01-DK117354). Dr. Reeder is a Romnes Faculty Fellow, and has received an award provided by the University of Wisconsin-Madison Office of the Vice Chancellor for Research and Graduate Education with funding from the Wisconsin Alumni Research Foundation. All funding was in compliance with ethical standards.

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Corresponding author

Correspondence to Diego Hernando.

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Guarantor

The scientific guarantor of this publication is Diego Hernando, PhD.

Conflicts of interest

The authors of this manuscript declare relationships with the following companies unrelated to this work: SBR has ownership interests in Calimetrix, Reveal Pharmaceuticals, Elucent Medical, Cellectar Biosciences, and HeartVista; DH has ownership interests in Calimetrix. SAW is a paid consultant for Ethicon Inc. The authors of this manuscript declare no relationships with any companies, whose products or services may be related to the subject matter of the article.

Statistics and biometry

No complex statistical methods were necessary for this paper.

Informed consent

Written informed consent was obtained from all subjects (patients) in this study.

Ethics approval

Institutional Review Board approval was obtained.

Study subjects or cohorts overlap

All of the subjects used in this manuscript were reported in a previous manuscript (https://pubmed.ncbi.nlm.nih.gov/32243665/) focused on the development of FAM-based fat quantification. However, the previous manuscript used separate FAM acquisitions obtained on these subjects, as well as different image processing and analysis.

Methodology

• prospective

• prospective cohort study

• performed at one institution

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Starekova, J., Zhao, R., Colgan, T.J. et al. Improved free-breathing liver fat and iron quantification using a 2D chemical shift–encoded MRI with flip angle modulation and motion-corrected averaging. Eur Radiol 32, 5458–5467 (2022). https://doi.org/10.1007/s00330-022-08682-x

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  • DOI: https://doi.org/10.1007/s00330-022-08682-x

Keywords

  • Flip angle modulation
  • NLM
  • Free-breathing
  • PDFF
  • R2*