不用b=0图像的活体组织体素内不相干运动分析：应用在肝脏纤维化评估的一个例子

摘要/Abstract

摘要： 体素内不相干运动(intravoxel incoherent motion,IVIM)成像系列的组成一般由开始没有弥散成像梯度磁场的成像(b=0s/mm²) 及一系列不同强度 (或不同持续时间) 的弥散成像梯度磁场的成像。在人体的许多器官,比如肝脏,b值与成像信号的关系一般分为两部分：①低b值时信号快速下降与组织内的血液灌注导致的快速水分子移位有关;②高b值时信号相对较为缓慢下降与组织内的水分子弥散相关。这些关系大致表现为b值系列与信号的双指数衰减下降关系,并由三个参数来表示即Dslow(D)、Dfast(D^*)、PF(f)。Dslow反映水分子弥散移位的快慢,Dfast反映血液灌注的水分子移位的快慢,PF反映灌注占的百分比。IVIM成像虽然理论上有许多优越性,但是以前常规描述的方式在临床医学中没有实际应用起来,其原因是公式拟合困难,测量结果不稳定。肝脏为富血供器官,适合IVIM观察,但是肝脏同时受到一些生理性运动的影响,比如呼吸运动以及心脏的跳动,左肝还受到胃内容物引起的磁敏感伪影的影响。最近我们发表了两个小型临床研究,第一个研究中有16位健康志愿者及33位乙型肝炎性肝纤维化患者(其中15例为1期肝纤维化);第二个研究中有26位健康志愿者及12位乙型肝炎性肝纤维化患者(其中4例为1期肝纤维化)。这两个研究中所有的健康人与肝纤维化患者均可以通过IVIM区别。而且,第二个研究中有4例活检病理无肝纤维化的患者,其IVIM结果与正常人类似。虽然迄今为止我们的IVIM扫描参数以及数据处理方式尚未最优化,我们推想,优良的结果是基于我们采取了下面的方法：①IVIM 数据分析去除b=0的图像;②仔细选择b值分布及合理选择分段拟阀值b;③去除质量不好的图像;④将所有的IVIM 参数考虑进临床判断。本文描述的IVIM评估肝脏纤维化的图像采集及图像后处理分析尚未最优化。可以预期,优化后的IVIM对于检出早期肝脏纤维化会有很高的敏感性及特异性。

关键词: 体素内不相干运动, 弥散成像, 肝脏, 纤维化

Abstract: With the reported intravoxel incoherent motion (IVIM) analyses, the diffusion image signal decay is computed starting from b=0 s/mm² image and then increasingly higher b-values using a biexponential decay model. In many organs such as the liver, the relationship between b-value and diffusion signal is composed of two parts: ① low b-values are associated with quick signal decay caused by fast moving water associated with blood perfusion; ② high b-values are associated with slow signal decay caused by pure water diffusion. These associations are represented by three parameters associated with a bi-exponential model, i.e. Dslow (D), Dfast (D^*), PF (f). PF is the fraction of the pseudo-diffusion linked to microcirculation, Dslow is the true diffusion coefficient representing the pure molecular diffusion, and Dfast is the perfusion-related diffusion. Although the theory of IVIM is very appealing, the practical application in the liver is difficult due to the difficulties in curve fitting and instability of results. Due to its relatively high blood supply, the liver is a very suitable organ for IVIM study. However, the liver is in the meantime particularly affected by physiological motions such as respiration and heart beating; meanwhile, the left liver is also affected by susceptibility artefact due to contents in the stomach. Recently we published two small cohort studies. Study-1 had 16 healthy volunteers and 33 viral hepatitis-b liver fibrosis patients among them 15 patients had stage-1 liver fibrosis. Study-2 had 26 healthy volunteers and 12 viral hepatitis-b liver fibrosis patients among them 4 patients had stage-1 liver fibrosis. All patients and healthy volunteers can be separated by IVIM analysis. Interestingly, study-2 had four patients with biopsy showing no or minimal fibrosis, and these four subjects’ IVIM measurements resembled healthy volunteers. While our current data acquisition and analysis still remain not optimal, we believe we were able to achieve these good results by the following measures: ①IVIM analysis without b=0 data; ②Carefully select b value distribution and the threshold b-value; ③ Discard poor image quality files; ④ Incorporating all IVIM parameters for consideration. We expect that with further improvement in data acquisition and post-processing, IVIM technique will have high sensitivity and specificity for early liver fibrosis evaluation.

Key words: Intravoxel incoherent motion, Diffusion, Liver, Fibrosis

王毅翔. 不用b=0图像的活体组织体素内不相干运动分析：应用在肝脏纤维化评估的一个例子[J]. 新发传染病电子杂志, 2019, 4(1): 8-14.

WANG Yi-xiang. Living tissue intravoxel incoherent motion (IVIM) diffusion MR analysis without b=0 image: an example for liver fibrosis evaluation[J]. Electronic Journal of Emerging Infectious Diseases, 2019, 4(1): 8-14.

参考文献

[1] Le Bihan D, Breton E, Lallemand D, et al.MR imaging of intravoxel incoherent motions: application to diffusion and perfusion in neurologic disorders[J]. Radiology, 1986, 161(2):401-407.
[2] Le Bihan D, Breton E, Lallemand D, et al.Separation of diffusion and perfusion in intravoxel incoherent motion MR imaging[J]. Radiology, 1988, 168(2):497-505.
[3] Le Bihan D, Turner R, Moonen CT, et al.Imaging of Diffusion and Microcirculation with Gradient Sensitization: Design, Strategy, and Significance[J]. J Magn Reson Imaging, 1991, 1(1):7-28.
[4] Yamada I, Aung W, Himeno Y, et al.Diffusion coefficients in aBdominal organs and hepatic lesions: evaluation with intravoxel incoherent motion echo-planar MR imaging[J]. Radiology, 1999, 210(3):617-23.
[5] Li YT, Cercueil JP, Yuan J, et al.Liver intravoxel incoherent motion (IVIM) magnetic resonance imaging: a comprehensive review of puBlished data on normal values and applications for fiBrosis and tumor evaluation[J]. Quant Imaging Med Surg, 2017, 7(1):59-78.
[6] Luciani A, Vignaud A, Cavet M,et al.Liver cirrhosis: intravoxel incoherent motion MR imaging--pilot study[J]. Radiology, 2008, 249(3):891-899.
[7] Guiu B, Petit JM, Capitan V, et al.Intravoxel incoherent motion diffusion-weighted imaging in nonalcoholic fatty liver disease: a 3.0-T MR study[J]. Radiology, 2012, 265(1):96-103.
[8] Andreou A, Koh DM, Collins DJ, et al.Measurement reproduciBility of perfusion fraction and pseudodiffusion coefficient derived By intravoxel incoherent motion diffusion-weighted MR imaging in normal liver and metastases[J]. Eur Radiol, 2013, 23(2):428-434.
[9] Wáng YX, Li YT, Chevallier O, Huang H, et al.Dependence of intravoxel incoherent motion diffusion MR threshold B-value selection for separating perfusion and diffusion compartments and liver fiBrosis diagnostic performance[J]. Acta Radiol, 2019,60(1):3-12.
[10] Wáng YX, Deng M, Li YT, et al.A ComBined Use of Intravoxel Incoherent Motion MRI Parameters Can Differentiate Early-Stage Hepatitis-B FiBrotic Livers from Healthy Livers[J]. SLAS Technol, 2018,23(3):259-268.
[11] Huang H, Che-Nordin N, Wang LF, et al.High performance of intravoxel incoherent motion diffusion MRI in detecting viral hepatitis-B induced liver fiBrosis[J]. Ann Transl Med, 2019,7(4):39.
[12] Cercueil JP, Petit JM, Nougaret S, et al.Intravoxel incoherent motion diffusion-weighted imaging in the liver: comparison of mono-, Bi- and tri-exponential modelling at 3.0-T[J]. Eur Radiol, 2015, 25(6):1541-1550.
[13] Chevallier O, Zhou N, Cercueil JP, et al.Comparison of tri-exponential decay vs. Bi-exponential decay and full fitting vs. segmented fitting for modeling liver intravoxel incoherent motion diffusion MRI[J]. BioRxiv, 2018; Available online: Comparison of tri-exponential decay vs. Bi-exponential decay and full fitting vs. segmented fitting for modeling liver intravoxel incoherent motion diffusion MRI[J]. BioRxiv, 2018; Available online: http://dx.doi.org/10.1101/429977.
[14] Le Bihan D. What can we see with IVIM MRI?[J].2017 Dec 22. doi: 10.1016/j.neuroimage.2017.12.062.
[15] Lemke A, Stieltjes B, Schad LR, et al.Toward an optimal distriBution of B values for intravoxel incoherent motion imaging[J]. Magn Reson Imaging, 2011, 29(6):766-776.
[16] Dyvorne H, Jajamovich G, Kakite S, et al.Intravoxel incoherent motion diffusion imaging of the liver: optimal B-value suBsampling and impact on parameter precision and reproduciBility[J]. Eur J Radiol, 2014, 83(12):2109-2113.
[17] ter Voert EE, Delso G, Porto M, et al. Intravoxel incoherent motion protocol evaluation and data quality in normal and malignant liver tissue and comparison to the literature[J]. Invest Radiol, 2016, 51(2):90-99.
[18] Wurnig MC, Donati OF, UlBrich E, et al. Systematic analysis of the intravoxel incoherent motion threshold separating perfusion and diffusion effects: Proposal of a standardized algorithm[J]. Magn Reson Med, 2015, 74(5):1414-1422.
[19] Chevallier O, Zhou N, He J, et al.Removal of evidential motion-contaminated and poorly fitted image data improves IVIM diffusion MRI parameter scan-rescan reproduciBility. Acta Radiol[J]. 2018, 59(6):1157-1167.
[20] Jean-Pierre Cercueil.一种诊断肝纤维化的有效方法–评Wang等体素内不相干运动MRI成像在区分早期肝纤维化与正常肝脏的论文[J].新发传染病电子杂志,2017,2(3):196-197.
[21] Do RK, Rusinek H, Taouli B.Dynamic contrast-enhanced MR imaging of the liver: current status and future directions[J]. Magn Reson Imaging Clin N Am, 2009, 17(2):339-49.
[22] Regini F, Colagrande S, Mazzoni LN, et al.Assessment of Liver Perfusion By IntraVoxel Incoherent Motion (IVIM) Magnetic Resonance-Diffusion-Weighted Imaging: Correlation With Phase-Contrast Portal Venous Flow Measurements[J]. J Comput Assist Tomogr, 2015, 39(3):365-72.
[23] Burkart DJ, Johnson CD, Reading CC, et al.MR measurements of mesenteric venous flow: prospective evaluation in healthy volunteers and patients with suspected chronic mesenteric ischemia[J]. Radiology 1995, 194(3):801-806.