Desrosiers Paul Audain, Michalowicz Gabrielle, Jouk Pierre-Simon, Usson Yves, Zhu Yuemin
CREATIS, CNRS UMR 5220, INSERM U1206, University of Lyon, INSA Lyon, Lyon 69621, France and TIMC-IMAG, CNRS UMR 5525, University of Grenoble Alps, Grenoble 38706, France.
TIMC-IMAG, CNRS UMR 5525, University of Grenoble Alps, Grenoble 38043, France and Genetics Department, CHU Grenoble-Alps, CS 10217 Grenoble, Grenoble Cedex 9 38043, France.
Med Phys. 2016 May;43(5):2273. doi: 10.1118/1.4945272.
The arrangement or architecture of myocardial cells plays a fundamental role in the heart's function and its change was shown to be directly linked to heart diseases. Inhomogeneity level is an important index of myocardial cell arrangements in the human heart. The authors propose to investigate the inhomogeneity level of myocardial cells using polarized light imaging simulations and experiments.
The idea is based on the fact that the myosin filaments in myocardial cells have the same properties as those of a uniaxial birefringent crystal. The method then consists in modeling the myosin filaments of myocardial cells as uniaxial birefringent crystal, simulating the behavior of the latter by means of the Mueller matrix, and measuring the final intensity of polarized light and consequently the inhomogeneity level of myocardial cells in each voxel through the use of crossed polarizers. The method was evaluated on both simulated and real tissues and under various myocardial cell configurations including parallel cells, crossed cells, and cells with random orientations.
When myocardial cells run perfectly parallel to each other, all the polarized light was blocked by those parallel myocardial cells, and a high homogeneity level was observed. However, if myocardial cells were not parallel to each other, some leakage of the polarized light was observed, thus causing the decrease of the polarized light amplitude and homogeneity level. The greater the crossing angle between myocardial cells, the smaller the amplitude of the polarized light and the greater the inhomogeneity level. For two populations of myocardial cell crossing at an angle, the resulting azimuth angle of the voxel was the bisector of this angle. Moreover, the value of the inhomogeneity level began to decrease from a nonzero value when the voxel was not totally homogeneous, containing for example cell crossing.
The proposed method enables the physical information of myocardial tissues to be estimated and the inhomogeneity level of a volume or voxel to be quantified, which opens new ways to study the microstructures of the human myocardium and helps understanding how heart diseases modify myocardial cells and change their mechanical properties.
心肌细胞的排列或结构在心脏功能中起着基础性作用，且其变化被证明与心脏病直接相关。不均匀性水平是人体心脏中心肌细胞排列的一个重要指标。作者提议利用偏振光成像模拟和实验来研究心肌细胞的不均匀性水平。
该想法基于心肌细胞中的肌球蛋白丝具有与单轴双折射晶体相同性质这一事实。该方法包括将心肌细胞的肌球蛋白丝建模为单轴双折射晶体，通过穆勒矩阵模拟后者的行为，并使用交叉偏振器测量偏振光的最终强度，从而确定每个体素中心肌细胞的不均匀性水平。该方法在模拟组织和真实组织上以及在各种心肌细胞配置（包括平行细胞、交叉细胞和随机取向细胞）下进行了评估。
当心肌细胞彼此完美平行时，所有偏振光都被那些平行的心肌细胞阻挡，观察到高均匀性水平。然而，如果心肌细胞彼此不平行，则会观察到一些偏振光泄漏，从而导致偏振光振幅和均匀性水平降低。心肌细胞之间的交叉角度越大，偏振光的振幅越小，不均匀性水平越高。对于以一定角度交叉的两群心肌细胞，体素的最终方位角是该角度的平分线。此外，当体素不完全均匀（例如包含细胞交叉）时，不均匀性水平的值从非零值开始下降。
所提出的方法能够估计心肌组织的物理信息并量化体积或体素的不均匀性水平，这为研究人类心肌的微观结构开辟了新途径，并有助于理解心脏病如何改变心肌细胞及其力学性能。
