6 Strain and Strain Rate Imaging
Basic Principles
Assessment of Left Ventricular Function
Defining Strain

Figure 6-1 Morphology of radial (above) and longitudinal (below) strain curves. Systolic strain (measured at aortic valve closure, AVC), may be exceeded by peak strain, and the difference may be measured in timing or strain magnitude (postsystolic shortening), usually measured as postsystolic index (PSI).

Figure 6-2 Parametric map of apical long axis in which colors express velocity (above) and strain rate magnitudes and timing (below) starting at the posterior and progressing to the anteroseptal wall. The example shows the relative sensitivity of strain rate imaging (SRI) to small regions of wall motion abnormality. An infarct in the posterior wall (zone A) is not detected by tissue velocity imaging, which shows a red color, consistent with movement toward the transducer. This is the same as the anterior wall (zone B) and reflects tethering by the remainder of the wall, causing translational movement within the infarct area (upper panel). Because of the site specificity of SRI, tethering does not alter the deformation of the risk area (zone A), which is identified correctly as infarcted (note the blue color in systole), and contrasts with the anterior wall (zone A), which shows a gold color, consistent with thickening (zone B). As this is a Doppler-based technique, the apex (zone C) is not well evaluated by either method.
Benefits of Strain

Figure 6-3 Regional variation of strain (A) and tissue velocity (B) in the septum. As the apex is fixed and the base moves away and toward this like a piston, there is a gradation of velocity from base (green) to apex (turquoise). In contrast, although there are minor regional variations of strain, strain values from apex and base are relatively uniform.
Disadvantages of Strain

Figure 6-4 Impact of angulation on strain measurement. In the apical view, the mid-septum (yellow) is closest to parallel with the ultrasound beam. As the incident angle increases towards 45 degrees, apparent strain measurement decreases (turquoise). In the apex, the incident angle increases to 90 degrees, so radial strain is measured, the strain direction being opposite to that of longitudinal strain.
Key Points
Methodologies

Figure 6-5 Myocardial imaging method. A, Tissue velocity imaging. B, Tissue velocity imaging (TVI)-based strain rate (SR) and strain. C, Speckle-based strain using velocity vector imaging. D, Speckle-based SR.
Tissue Doppler-based Strain
Speckle-based Strain
Speckle- versus TVI-based Strain

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