Wong Rochelle E, Tasdelen Bilal, Tian Ye, Hwang Darryl, Cui Sophia X, Yuan Liyun, Nayak Krishna S
Division of Gastroenterology and Hepatology, University of Southern California Keck Medical Center, 1510 San Pablo St., HC1 - Suite 200, Los Angeles, CA, 90033, USA.
Ming Hsieh Department of Electrical and Computer Engineering, University of Southern California, Los Angeles, CA, USA.
MAGMA. 2025 Jul 15. doi: 10.1007/s10334-025-01277-9.
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.
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.
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.
In the phantom, there was excellent match (R > 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%.
Our data demonstrate that 0.55 T MRI is feasible and comparable to 3 T MRI in quantifying liver PDFF among patients with MASLD.
质子密度脂肪分数（PDFF）——无干扰脂肪信号与无干扰脂肪和水信号总和的比值，是代谢相关脂肪性肝病（MASLD）一种有价值的定量成像生物标志物，广泛应用于临床实践和临床试验。肝脏的PDFF通常使用3T MRI系统进行测量。然而，低场系统因其成本较低、安全性提高、金属植入物周围伪影最小化以及患者舒适度提高而越来越受到青睐。
在这项初步研究中，我们利用标准化且广泛使用的3T肝脏PDFF方案的知识，并调整参数使其适用于0.55T MRI。我们评估了0.55T时的肝脏脂肪定量方案与标准临床3T方案相比，用于测量MASLD患者肝脏脂肪的情况。
8名在3T MRI上PDFF≥5%的成年患者（平均年龄53.6±13.6岁，5名女性）在90天内接受了0.55T MRI的PDFF方案。为了将采集时间控制在合理的屏气持续时间内并保持合理的信噪比（SNR），与使用6回波多回波狄克逊容积内插屏气检查（VIBE）方案的3T相比，0.55T以较低分辨率和较少层数采集了4个回波。使用商用PDFF体模和体内评估0.55T方法的PDFF定量准确性。
在体模中，0.55T MRI估计的PDFF与真实值之间有极好的匹配度（R>0.999）。3T MRI体内平均PDFF为16.5%，而0.55T MRI体内平均PDFF为16.3%（相关系数r = 0.99）。布兰德-奥特曼分析显示，0.55T和3T的体内PDFF测量结果具有良好的一致性，偏差或平均差异为-0.25%，一致性界限（LoA）为-3.98%和3.48%。
我们的数据表明，在量化MASLD患者的肝脏PDFF方面，0.55T MRI是可行的，且与3T MRI相当。
