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

• Published in: European radiology Vol. 32; no. 8; pp. 5458 - 5467
• Main Authors: Starekova, Jitka, Zhao, Ruiyang, Colgan, Timothy J., Johnson, Kevin M., Rehm, Jennifer L., Wells, Shane A., Reeder, Scott B., Hernando, Diego
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01-08-2022; Springer Nature B.V
• Subjects: Bias; Biomarkers; Chemical equilibrium; Diagnostic Radiology; Image acquisition; Image processing; Image quality; Imaging; Internal Medicine; Interventional Radiology; Iron; Liver; Magnetic Resonance; Magnetic resonance imaging; Medical imaging; Medicine; Medicine & Public Health; Neuroradiology; Proton density (concentration); Radio frequency; Radiology; Regression analysis; Repetition; Signal to noise ratio; Three dimensional motion; Ultrasound; R2; PDFF; Flip angle modulation; NLM; Free-breathing
• ISSN: 1432-1084; 0938-7994; 1432-1084
• DOI: 10.1007/s00330-022-08682-x

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,
R
2
= 0.996) for PDFF and good agreement (regression slope 1.08–1.15,
R
2
≥ 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.