铁过载状态下的脂肪定量的局限性。
Limits of Fat Quantification in the Presence of Iron Overload.
机构信息
Department of Radiology, University of Wisconsin, Madison, Wisconsin, USA.
Department of Electrical and Computer Engineering, University of Wisconsin, Madison, Wisconsin, USA.
出版信息
J Magn Reson Imaging. 2021 Oct;54(4):1166-1174. doi: 10.1002/jmri.27611. Epub 2021 Mar 29.
BACKGROUND
Chemical shift encoded magnetic resonance imaging (CSE-MRI)-based tissue fat quantification is confounded by increased R2* signal decay rate caused by the presence of excess iron deposition.
PURPOSE
To determine the upper limit of R2* above which it is no longer feasible to quantify proton density fat fraction (PDFF) reliably, using CSE-MRI.
STUDY TYPE
Prospective.
POPULATION
Cramér-Rao lower bound (CRLB) calculations, Monte Carlo simulations, phantom experiments, and a prospective study in 26 patients with known or suspected liver iron overload.
FIELD STRENGTH/SEQUENCE: Multiecho gradient echo at 1.5 T and 3.0 T.
ASSESSMENT
CRLB calculations were used to develop an empirical relationship between the maximum R2* value above which PDFF estimation will achieve a desired number of effective signal averages. A single voxel multi-TR, multi-TE stimulated echo acquisition mode magnetic resonance spectroscopy acquisition was used as a reference standard to estimate PDFF. Reconstructed PDFF and R2* maps were analyzed by one analyst using multiple regions of interest drawn in all nine Couinaud segments.
STATISTICAL TESTS
None.
RESULTS
Simulations, phantom experiments, and in vivo measurements demonstrated unreliable PDFF estimates with increased R2*, with PDFF errors as large as 20% at an R2* of 1000 s . For typical optimized Cartesian acquisitions (TE1 = 0.75 msec, ΔTE = 0.67 msec at 1.5 T, TE1 = 0.65 msec, ΔTE = 0.58 msec at 3.0 T), an empirical relationship between PDFF estimation errors and acquisition parameters was developed that suggests PDFF estimates are unreliable above an R2* of ~538 s and ~779 s at 1.5 T and 3 T, respectively. This empirical relationship was further investigated with phantom experiments and in vivo measurements, with PDFF errors at an R2* of 1000 s at 3.0 T as large as 10% with TE1 = 1.24 msec, ΔTE = 1.01 msec compared to 3% with TE1 = 0.65 msec, ΔTE = 0.58 msec.
DATA CONCLUSION
We successfully developed a theoretically-based empirical formula that may provide an easily calculable guideline to identify R2* values above which PDFF is not reliable in research and clinical applications using CSE-MRI to quantify PDFF in the presence of iron overload.
LEVEL OF EVIDENCE
1 TECHNICAL EFFICACY STAGE: 1.
背景
基于化学位移编码磁共振成像（CSE-MRI）的组织脂肪定量会受到过量铁沉积引起的 R2*信号衰减率增加的影响。
目的
使用 CSE-MRI 确定 R2*值上限，超过该上限后，可靠地定量质子密度脂肪分数（PDFF）已不再可行。
研究类型
前瞻性。
人群
Cramér-Rao 下限（CRLB）计算、蒙特卡罗模拟、体模实验以及 26 例已知或疑似肝铁过载患者的前瞻性研究。
磁场强度/序列：1.5T 和 3.0T 多回波梯度回波。
评估
CRLB 计算用于开发一个经验关系，该关系将确定最大 R2值，超过该值后，PDFF 估计将达到所需的有效信号平均次数。使用单像素多重复 TR、多 TE 激发回波采集模式磁共振波谱采集作为参考标准来估计 PDFF。使用在所有九个 Couinaud 段中绘制的多个感兴趣区域对重建的 PDFF 和 R2图进行分析。
统计学检验
无。
结果
模拟、体模实验和体内测量显示，随着 R2的增加，PDFF 估计不可靠，在 R2为 1000s 时，PDFF 误差最大可达 20%。对于典型的优化笛卡尔采集（1.5T 时 TE1=0.75ms，ΔTE=0.67ms，TE1=0.65ms，ΔTE=0.58ms；3.0T 时），开发了一个 PDFF 估计误差与采集参数之间的经验关系，表明在 1.5T 和 3.0T 时，PDFF 估计分别在 R2约 538s 和 779s 以上不可靠。该经验关系进一步通过体模实验和体内测量进行了研究，在 3.0T 时 R2为 1000s 时，TE1=1.24ms，ΔTE=1.01ms 时 PDFF 误差高达 10%，而 TE1=0.65ms，ΔTE=0.58ms 时 PDFF 误差为 3%。
数据结论
我们成功开发了一种基于理论的经验公式，该公式可能为使用 CSE-MRI 量化铁过载时的 PDFF 提供一个易于计算的指南，以确定 R2*值上限，超过该上限后，PDFF 不可靠。
证据水平
1 技术功效分期：1。
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