3.0T MR扩散张量成像在心肌梗死后微观结构重构中的监测价值

Evaluation of microstructure remodeling after myocardial infarction using 3.0 T magnetic resonance imaging

目的运用3.0 T MR扩散张量成像(diffusion tensor imaging,DTI)对心肌梗死后梗死区、边缘区及非梗死区的心肌重构进行动态监测,以发现心室重构的规律性和异质性。材料与方法选用50只成年雄性兔,分为正常组(5只),假手术组(5只)和实验组(40只),实验组根据心肌梗死术后1、2、4、8周及16周分为5个亚组(8只)。通过结扎冠状动脉左室支,建立兔心肌梗死模型,术后死亡7只,实验组存活33只。将离体兔心脏标本进行3.0 T DTI扫描,测量梗死区、边缘区和非梗死区的各向异性分数(fractional anisotropy,FA)值和平均扩散系数(mean diffusion coefficient,MD)值,动态观察DTI指标的演变过程。结果 (1)梗死区和边缘区的FA值在术后第1周时均显著下降,之后下降较缓慢,均在第4周时达最低。之后梗死区FA基本稳定,而边缘区FA小幅度升高至8周时稳定。(2)在术后4周内,梗死区MD呈迅速明显上升趋势而边缘区MD渐进性轻度升高,两者均是在第4周时达高峰。之后梗死区MD基本稳定至8周,在第16周时有小幅度下降。边缘区MD在第8周时轻度下降,之后稳定。结论心肌梗死后心室重构是复杂且动态变化的过程,在心梗后第1周内,梗死区和边缘区组织重构最为迅速且明显,在第4周时重构达高峰,即组织破坏最为严重,心梗长达8周后重构基本稳定。DTI能够揭示心室不同区域重构的规律性,对指导临床治疗有着重要意义。

Objective： To detect myocardial microstructure remodeling dynamically in the core-infarction zone（CIZ）, peri-infarction zone（PIZ） and non-infarction zone（NIZ） using 3.0 T diffusion tensor imaging, so as to find out the ventricular remodeling（VR） mechanism and heterogeneity. Materials and Methods： Fifty adult male rabbits were split into a normal group（n=5）, a sham-operation group（n=5）, and a myocardial infarction（MI） group（n=40）, the MI group was further split into 5 subgroups at 1, 2, 4, 8 weeks, and 16 weeks after operation, while 33 survived and 7 died. The rabbit MI model was established by ligating the left ventricular branch of the coronary artery. The vitro heart specimens were gained to proceed the 3.0 T DTI. Fractional anisotropy（FA） and mean diffusion（MD） coefficient values were measured in the CIZ, PIZ and NIZ. DTI indicators were monitored dynamically. Results：（1）Both the FA values of the CIZ and PIZ significantly decreased in the 1st week, then decreased slowly, both reached the lowest values at the 4th week. Then the FA of the CIZ tended to be stable, while in the PIZ, they appeared a small increase and became stable at the 8th week.（2）The MD values in the CIZ increased rapidly and dramatically in the 4th week after operation, while those in the PIZ increased slowly and gradually, both reaching the peak at the 4th week synchronously. Subsequently, the MD of the CIZ stayed stable until the 8th week, then decreased slightly at the 16 th week. The MD of the PIZ decreased slowly and became stable at the 8th week. Conclusions： Ventricular remodeling after myocardial infarction was a complex and dynamic process, the CIZ and PIZ remodeled very quickly and obviously in the 1st week, and reached the peak at the 4th week, which meant the tissue destruction was the most serious, then remodeling stayed stable until the 8th week. DTI can reveal the remodeling regularity in different areas and play an important role on the guidance for clinical treatment.