Wedeen V J
Department of Radiology, Massachusetts General Hospital, Boston 02114.
Magn Reson Med. 1992 Sep;27(1):52-67. doi: 10.1002/mrm.1910270107.
A magnetic resonance imaging (MRI) method is presented to detect, localize, and quantify myocardial kinematics by measuring the material rate-of-strain tensor at each pixel in gated NMR images of the heart. The immediate, local effect of muscular activity is self-deformation, and the strain tensor is the basic mathematical device by which such deformation may be quantified. The present method, called "strain-phase" MRI (SP-MRI), entails four steps: (1) the velocity of the myocardium is encoded by means of a set of motion-sensitive NMR image acquisitions, one image per velocity component; (2) the spatial derivatives of the velocity are computed at each pixel; (3) the velocity-derivative data are combined to compute an approximation of the strain-rate tensor of the myocardium at each pixel; and (4) the strain-rate tensor data are simplified to produce a color-coded functional image which represents strain-rate components which are of particular biomedical interest in the myocardium. We present a quantitative SP-MRI methodology suited to conventional MRI, and in addition present an "echo-planar" methodology, able to produce qualitative functional images of myocardial kinematics at almost real-time speeds. Two-dimensional strain-phase MRI data acquired in normal human subjects are presented. These data demonstrate the practicability of SP-MRI in vivo, that SP-MRI resolves myocardial kinematics at the single-pixel scale, having resolution comparable to that of conventional MRI, and that SP-MRI data may have a signal-to-noise ratio up to 50% as great as that of the conventional MRI data from which they are produced. SP-MRI measurements of the local instantaneous strain rates in the human left ventricular myocardium are quantitatively consistent with known transmural average values of myocardial strain.
本文提出了一种磁共振成像（MRI）方法，通过测量心脏门控NMR图像中每个像素处的材料应变率张量，来检测、定位和量化心肌运动学。肌肉活动的直接局部效应是自身变形，而应变张量是量化这种变形的基本数学工具。目前的方法称为“应变相位”MRI（SP-MRI），包括四个步骤：（1）通过一组运动敏感的NMR图像采集对心肌速度进行编码，每个速度分量采集一幅图像；（2）计算每个像素处速度的空间导数；（3）合并速度导数数据，以计算每个像素处心肌应变率张量的近似值；（4）简化应变率张量数据，以生成一个彩色编码的功能图像，该图像表示心肌中具有特定生物医学意义的应变率分量。我们提出了一种适用于传统MRI的定量SP-MRI方法，此外还提出了一种“回波平面”方法，该方法能够以几乎实时的速度生成心肌运动学的定性功能图像。展示了在正常人类受试者中获取的二维应变相位MRI数据。这些数据证明了SP-MRI在体内的实用性，即SP-MRI在单像素尺度上解析心肌运动学，其分辨率与传统MRI相当，并且SP-MRI数据的信噪比可能高达其产生所基于的传统MRI数据的50%。SP-MRI对人类左心室心肌局部瞬时应变率的测量在定量上与已知的心肌跨壁平均值一致。
