Luo Jianwen, Fujikura Kana, Homma Shunichi, Konofagou Elisa E
Department of Biomedical Engineering, Columbia University, New York, NY 10027, USA.
Ultrasound Med Biol. 2007 Aug;33(8):1206-23. doi: 10.1016/j.ultrasmedbio.2007.01.019. Epub 2007 Jun 13.
Myocardial elastography is a novel method for noninvasively assessing regional myocardial function, with the advantages of high spatial and temporal resolution and high signal-to-noise ratio (SNR). In this paper, in-vivo experiments were performed in anesthetized normal and infarcted mice (one day after left anterior descending coronary artery [LAD] ligation) using a high-resolution (30 MHz) ultrasound system (Vevo 770, VisualSonics Inc., Toronto, ON, Canada). Radiofrequency (RF) signals of the left ventricle (LV) in longitudinal (long-axis) view and the associated electrocardiogram (ECG) were simultaneously acquired. Using a retrospective ECG gating technique, 2-D full field-of-view RF frames were acquired at an extremely high frame rate (8 kHz) that resulted in high-quality incremental displacement and strain estimation of the myocardium. The incremental results were further accumulated to obtain the cumulative displacements and strains. Two-dimensional and M-mode displacement images and strain images (elastograms), as well as displacement and strain profiles as a function of time, were compared between normal and infarcted mice. Incremental results clearly depicted cardiac events including LV contraction, LV relaxation and isovolumetric phases in both normal and infarcted mice, and also evidently indicated reduced motion and deformation in the infarcted myocardium. The elastograms indicated that the infarcted regions underwent thinning during systole rather than thickening, as in the normal case. The cumulative elastograms were found to have higher elastographic SNR (SNR(e)) than the incremental elastograms (e.g., 10.6 vs. 4.7 in a normal myocardium, and 6.0 vs. 2.4 in an infarcted myocardium). Finally, preliminary statistical results from nine normal (m = 9) and seven infarcted (n = 7) mice indicated the capability of the cumulative strain in differentiating infracted from normal myocardia. In conclusion, myocardial elastography could provide regional strain information at simultaneously high temporal (>/=0.125 ms) and spatial ( approximately 55 microm) resolution as well as high precision ( approximately 0.05 microm displacement). This technique was thus capable of accurately characterizing normal myocardial function throughout an entire cardiac cycle, at the same high resolution, and detecting and localizing myocardial infarction in vivo.
心肌弹性成像术是一种用于无创评估局部心肌功能的新方法，具有高空间和时间分辨率以及高信噪比（SNR）的优点。在本文中，使用高分辨率（30 MHz）超声系统（Vevo 770，VisualSonics公司，加拿大多伦多）对麻醉后的正常小鼠和梗死小鼠（左冠状动脉前降支[LAD]结扎后一天）进行了体内实验。同时采集左心室（LV）纵切（长轴）视图中的射频（RF）信号以及相关的心电图（ECG）。采用回顾性心电图门控技术，以极高的帧率（8 kHz）采集二维全视野RF帧，从而实现对心肌的高质量增量位移和应变估计。将增量结果进一步累加，以获得累积位移和应变。比较了正常小鼠和梗死小鼠的二维和M型位移图像、应变图像（弹性图）以及位移和应变随时间变化的曲线。增量结果清晰地描绘了正常小鼠和梗死小鼠的心脏事件，包括左心室收缩、左心室舒张和等容相，并且还明显显示梗死心肌的运动和变形减少。弹性图表明，梗死区域在收缩期变薄而非增厚，与正常情况不同。发现累积弹性图比增量弹性图具有更高的弹性成像信噪比（SNR(e)）（例如，正常心肌中为10.6对4.7，梗死心肌中为6.0对2.4）。最后，来自9只正常小鼠（m = 9）和7只梗死小鼠（n = 7）的初步统计结果表明，累积应变能够区分梗死心肌和正常心肌。总之，心肌弹性成像术能够在同时具有高时间（>/=0.125 ms）和空间（约55微米）分辨率以及高精度（约0.05微米位移）的情况下提供局部应变信息。因此，该技术能够以相同的高分辨率在整个心动周期中准确表征正常心肌功能，并在体内检测和定位心肌梗死。
