In-vivo liver proton density fat fraction quantification at 0.55 T: a pilot study with comparison against 3 T MRI.

BACKGROUND

Proton density fat fraction (PDFF)- the ratio of unconfounded fat signal to the sum of the unconfounded fat and water signals, is a valuable quantitative imaging biomarker of metabolic associated steatotic liver disease (MASLD) widely applied in clinical practice and clinical trials. PDFF of the liver is commonly measured using 3 T MRI systems. However, low-field systems are increasingly favored due to lower cost, improved safety profile, minimized artifacts around metallic implants, and enhanced patient comfort.

OBJECTIVE

In this pilot study, we used knowledge of standardized and widely used 3 T liver PDFF protocols, and adapted parameters to be appropriate for the 0.55 T MRI. We evaluate a liver fat quantification protocol at 0.55 T compared to a standard clinical 3 T protocol to measure liver fat in patients with MASLD.

MATERIAL AND

METHODS

Eight adult patients (average age 53.6 ± 13.6 years, 5 females) with ≥ 5% PDFF on 3 T MRI underwent a 0.55 T MRI PDFF protocol within 90 days. To keep the acquisition time to be within a reasonable breath hold duration and with reasonable signal-to-noise ratio (SNR), four echoes were acquired at a lower resolution and fewer number of slices at 0.55 T compared to 3 T which uses a 6-echo multi-echo Dixon volumetric interpolated breath hold examination (VIBE) protocol. PDFF quantification accuracy of the 0.55 T approach was evaluated using a commercial PDFF phantom and in vivo.

RESULTS

In the phantom, there was excellent match (R2 > 0.999) between PDFF estimated by 0.55 T MRI and ground truth. Mean in vivo 3 T MRI-PDFF was 16.5%, compared to 16.3% 0.55 T MRI-PDFF (correlation coefficient r = 0.99). The Bland-Altman analysis showed good agreement of in vivo PDFF measurements across 0.55 T and 3 T estimating a bias or mean difference of - 0.25% and the limits of agreements (LoA) of - 3.98% and 3.48%.

DISCUSSION: Our data demonstrate that 0.55 T MRI is feasible and comparable to 3 T MRI in quantifying liver PDFF among patients with MASLD.