COMPENSATING FOR ANISOTROPY IN MYOCARDIAL ULTRASOUND

拟议研究的总体目标是促进 心肌病理无创检测与评价 基于组织的定量超声表征 本身，而不是评估尺寸或运动。 以前的研究表明，综合（频率平均） 反向散射显示了心肌组织表征的前景。 时间平均（在心动周期内）背向散射积分 在缺血心肌中升高。 此外，心肌 收缩和松弛被一个周期性的变化所代替， 积分反向散射，即使在 狗短暂缺血，再灌注后恢复。 一 将这些研究结果扩展到 患者的结果是， 心肌的结构引起系统变化（即， 各向异性）在其超声性质中。 的临床应用 超声组织表征要求测量结果 通过以不同角度传播超声波而制成， 相对于心脏的平均纤维取向， 在收缩-舒张周期中。 成功 用超声表征心肌需要 补偿这种角度变化的影响。 我们 建议研究超声特性的各向异性 及其与心脏依赖性变异的关系 心肌背向散射： 1)通过测量心肌的角度依赖性， 在开胸和闭胸狗体内的反向散射， 2)通过描述负责观察到的 通过应用时域在心肌中的各向异性 超声波散射的低对比度近似 圆柱形散射体，以及 3)通过评估临床组织的各向异性的后果 通过标准超声心动图进行表征 在正常志愿者和患者的研究中， 有记录的远端梗死或肥厚性 心肌病 这项研究的结果应允许实施 适当补偿各向异性的影响， 通过有助于提高超声的诊断能力， 组织定征的基础， 高分辨率超声成像的模式。

The overall objective of the proposed research is to contribute to the noninvasive detection and evaluation of myocardial pathology based on quantitative ultrasonic characterization of the tissue itself, as opposed to assessment of dimensions or motion. Previous research suggests that integrated (frequency averaged) backscatter shows promise for myocardial tissue characterization. The time averaged (over the heart cycle) integrated backscatter is elevated in ischemic myocardium. Furthermore, myocardial contraction and relaxation are paralleled by a cyclic variation in integrated backscatter, which is reduced substantially with even brief ischemia in dogs, and which recovers with reperfusion. A significant obstacle for extending these findings to studies of patients results from the fact that spatial orientation of the structure of myocardium gives rise to systematic variations (i.e., anisotropy) in its ultrasonic properties. Clinical applications of ultrasonic tissue characterization require measurements to be made with the propagation of ultrasound at varying angles with respect to the average fiber orientation of the heart and throughout the contraction-relaxation cycle. Successful characterization of myocardium with ultrasound will require compensation for the effects of this angular variation. We propose to investigate the anisotropy in the ultrasonic properties of the heart and their relationships to cardiac-dependent variation in myocardial backscatter: 1) by measuring the angular dependence of myocardial backscatter in vivo in open- and closed-chest dogs, 2) by characterizing the mechanisms responsible for the observed anisotropy in myocardium through application of a time domain low contrast approximation for the scattering of ultrasonic waves from cylindrical scatterers, and 3) by evaluating the consequences of anisotropy for clinical tissue characterization carried out through standard echocardiographic windows in studies of normal volunteers and patients with documented scar from remote infarct or with hypertrophic cardiomyopathy. Results of this research should permit the implementation of appropriate compensation for the effects of anisotropy and thus broaden the diagnostic power of ultrasound by contributing to the foundation of tissue characterization as a complementary modality to high resolution ultrasonic imaging.