1 Departments of Radiology and Medical Physics, University of Wisconsin School of Medicine and Public Health, 600 Highland Ave, Madison, WI 53705.
AJR Am J Roentgenol. 2018 Sep;211(3):W151-W157. doi: 10.2214/AJR.17.19391. Epub 2018 Jul 17.
The purpose of this study was to evaluate the relation between unenhanced CT liver attenuation values and MRI-derived proton density fat fraction (PDFF) for estimation of liver fat content at CT.
A CT-MRI phantom was constructed and imaged containing 12 vials with lipid fractions ranging from 0% to 100%. For the retrospective clinical arm, 221 patients (120 men, 101 women; mean age, 54 years) underwent both unenhanced CT and chemical shift-encoded MRI of the liver between 2007 and 2017. Among these patients, 92 had more than one 120-kV CT scan for comparison. CT attenuation and MRI PDFF were derived with coregistered ROI measurements in the right hepatic lobe. The 120-kV subgroup of CT examinations performed within 1 month of MRI PDFF examinations (n = 72) served as the primary cohort for linear correlation. The effects of different tube voltage settings, time intervals between CT and MRI, and iron overload were assessed. Linear least squares regression analysis was performed.
Phantom results showed excellent linear fit between CT attenuation and MRI PDFF (r = 0.986). In patients, 120-kV CT performed within 1 month of MRI PDFF exhibited strong linear correlation (r = 0.828) that closely matched the phantom data, yielding the following clinical CT-MRI conversion formula: MRI PDFF (%) = -0.58 × CT attenuation (HU) + 38.2. Correlation worsened for CT-to-MRI intervals longer than 1 month (r = 0.565), and this specific relationship did not apply as well to non-120-kV settings (r = 0.554). For patients with multiple scans, correlation progressively worsened over time. CT-based liver fat content was underestimated in several patients with iron overload.
The linear correlation between unenhanced CT attenuation and MRI PDFF allows quantification of liver fat content by means of unenhanced CT in clinical practice. As expected, correlation worsened with increasing CT-MRI time interval, variable tube voltage settings, and iron overload.
本研究旨在评估 CT 平扫肝脏衰减值与 MRI 衍生质子密度脂肪分数（PDFF）之间的关系，以评估 CT 肝脏脂肪含量的估计。
构建并成像了包含 12 个小瓶的 CT-MRI 体模，脂质分数范围为 0%至 100%。在回顾性临床臂中，2007 年至 2017 年间，221 例患者（120 例男性，101 例女性；平均年龄 54 岁）接受了 CT 平扫和化学位移编码 MRI 检查。其中 92 例患者有多个 120kV CT 扫描进行比较。在右肝叶中进行配准 ROI 测量，得出 CT 衰减和 MRI PDFF。在 MRI PDFF 检查后 1 个月内进行的 120kV CT 亚组检查（n=72）作为线性相关性的主要队列。评估了不同管电压设置、CT 和 MRI 之间的时间间隔以及铁过载的影响。进行线性最小二乘回归分析。
体模结果显示 CT 衰减与 MRI PDFF 之间具有极好的线性拟合（r=0.986）。在患者中，120kV CT 在 MRI PDFF 后 1 个月内进行，表现出强烈的线性相关性（r=0.828），与体模数据非常吻合，产生了以下临床 CT-MRI 转换公式：MRI PDFF（%）=-0.58×CT 衰减（HU）+38.2。CT-MRI 间隔大于 1 个月时相关性变差（r=0.565），这种特定关系不适用于非 120kV 设置（r=0.554）。对于有多个扫描的患者，随着时间的推移，相关性逐渐恶化。在几个铁过载患者中，CT 基于的肝脂肪含量被低估。
CT 平扫衰减值与 MRI PDFF 之间的线性相关性可通过 CT 平扫在临床实践中定量肝脏脂肪含量。正如预期的那样，随着 CT-MRI 时间间隔、管电压设置和铁过载的增加，相关性会变差。
