Motion-resolved fat-fraction mapping with whole-heart free-running multiecho GRE and pilot tone

Adèle L C Mackowiak; Christopher W Roy; Jérôme Yerly; Mariana B L Falcão; Mario Bacher; Peter Speier; Davide Piccini; Matthias Stuber; Jessica A M Bastiaansen

doi:10.1002/mrm.29680

Motion-resolved fat-fraction mapping with whole-heart free-running multiecho GRE and pilot tone

Magn Reson Med. 2023 Sep;90(3):922-938. doi: 10.1002/mrm.29680. Epub 2023 Apr 27.

Authors

Adèle L C Mackowiak^{1

2

3}, Christopher W Roy³, Jérôme Yerly^{3

4}, Mariana B L Falcão³, Mario Bacher^{3

5}, Peter Speier⁵, Davide Piccini^{3

6}, Matthias Stuber^{3

4}, Jessica A M Bastiaansen^{1

2}

Affiliations

¹ Department of Diagnostic, Interventional and Pediatric Radiology (DIPR), Inselspital, Bern University Hospital, University of Bern, Bern, Switzerland.
² Translation Imaging Center (TIC), Swiss Institute for Translational and Entrepreneurial Medicine, Bern, Switzerland.
³ Department of Radiology, Lausanne University Hospital (CHUV) and University of Lausanne (UNIL), Lausanne, Switzerland.
⁴ Center for Biomedical Imaging (CIBM), Lausanne, Switzerland.
⁵ Siemens Healthcare GmbH, Erlangen, Germany.
⁶ Advanced Clinical Imaging Technology (ACIT), Siemens Healthcare AG, Lausanne, Switzerland.

PMID: 37103471
DOI: 10.1002/mrm.29680

Abstract

Purpose: To develop a free-running 3D radial whole-heart multiecho gradient echo (ME-GRE) framework for cardiac- and respiratory-motion-resolved fat fraction (FF) quantification.

Methods: (N_TE = 8) readouts optimized for water-fat separation and quantification were integrated within a continuous non-electrocardiogram-triggered free-breathing 3D radial GRE acquisition. Motion resolution was achieved with pilot tone (PT) navigation, and the extracted cardiac and respiratory signals were compared to those obtained with self-gating (SG). After extra-dimensional golden-angle radial sparse parallel-based image reconstruction, FF, R₂ *, and B₀ maps, as well as fat and water images were generated with a maximum-likelihood fitting algorithm. The framework was tested in a fat-water phantom and in 10 healthy volunteers at 1.5 T using N_TE = 4 and N_TE = 8 echoes. The separated images and maps were compared with a standard free-breathing electrocardiogram (ECG)-triggered acquisition.

Results: The method was validated in vivo, and physiological motion was resolved over all collected echoes. Across volunteers, PT provided respiratory and cardiac signals in agreement (r = 0.91 and r = 0.72) with SG of the first echo, and a higher correlation to the ECG (0.1% of missed triggers for PT vs. 5.9% for SG). The framework enabled pericardial fat imaging and quantification throughout the cardiac cycle, revealing a decrease in FF at end-systole by 11.4% ± 3.1% across volunteers (p < 0.0001). Motion-resolved end-diastolic 3D FF maps showed good correlation with ECG-triggered measurements (FF bias of -1.06%). A significant difference in free-running FF measured with N_TE = 4 and N_TE = 8 was found (p < 0.0001 in sub-cutaneous fat and p < 0.01 in pericardial fat).

Conclusion: Free-running fat fraction mapping was validated at 1.5 T, enabling ME-GRE-based fat quantification with N_TE = 8 echoes in 6:15 min.

Keywords: 3D radial; cardiac MRI; fat quantification; motion; multiecho GRE; parametric mapping; pilot tone.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Electrocardiography
Heart* / diagnostic imaging
Humans
Image Processing, Computer-Assisted / methods
Imaging, Three-Dimensional / methods
Magnetic Resonance Imaging* / methods
Respiration