Addressing concomitant gradient phase errors in time-interleaved chemical shift-encoded MRI fat fraction and R 2 mapping with a pass-specific phase fitting method

• Published in: Magnetic resonance in medicine 2022-06, Vol.87 (6), p.2826-2838
• Main Authors: Roberts, Nathan T, Hernando, Diego, Panagiotopoulos, Nikolaos, Reeder, Scott B
• Format: Article
• Language: English
• Subjects: Adipose Tissue - diagnostic imaging; Humans; Liver - diagnostic imaging; Liver - metabolism; Magnetic Resonance Imaging - methods; Phantoms, Imaging; Protons; Reproducibility of Results
• ISSN: 0740-3194; 1522-2594
• DOI: 10.1002/mrm.29175

Concomitant gradients induce phase errors that increase quadratically with distance from isocenter. This work proposes a complex-based fitting method that addresses concomitant gradient phase errors in chemical shift encoded (CSE) MRI estimation of proton density fat fraction (PDFF) and R through joint estimation of pass-specific phase terms. This method is applicable to time-interleaved multi-echo gradient-echo acquisitions (i.e., multi-pass acquisitions) and does not require prior knowledge of gradient waveforms typically needed to address concomitant gradient phase errors. A CSE-MRI spoiled gradient echo signal model, with pass-specific phase terms, is introduced for non-linear least squares estimation of PDFF and R in the presence of concomitant gradient phase errors. Cramér-Rao lower bound analysis was used to determine noise performance tradeoffs of the proposed fitting method, which was then validated in both phantom and in vivo experiments. The proposed fitting method removed PDFF and R estimation errors up to 12% and 10 s , respectively, at ±12 cm off isocenter (S/I) in a water phantom. In healthy volunteers, PDFF and R bias was reduced by ~10% (12 cm off-isocenter) and ~30 s (16 cm off-isocenter), respectively. An evaluation in 29 clinical liver datasets demonstrated reduced PDFF bias and variability (8.4% improvement in the coefficient of variation), even with the imaging volume centered at isocenter. Concomitant gradient induced phase errors in multi-pass CSE-MRI acquisitions can result in PDFF and R estimation biases away from isocenter. The proposed fitting method enables accurate PDFF and R quantification in the presence of concomitant gradient phase errors without knowledge of imaging gradient waveforms.