Speckle tracking echocardiography (STE) is a new, non-invasive method for the assessment of left ventricular (LV) global and regional function. STE offers the opportunity to track myocardial deformation independently of both cardiac translation and the insonation angle. Before the advent of STE, the only technique for angle-independent assessment of LV deformation and rotation was tagged cardiac magnetic resonance (cMR). Although tagged cMR remains the reference method for the assessment of LV deformation, its use is limited by an inherent low frame rate acquisition, high cost, and time-consuming and complex data analysis. Recently, STE was proposed as an alternative method to assess LV deformation and torsion, and it has been systematically validated by reference to sonomicrometry, tagged cMR and colour-coded tissue Doppler echocardiography. Several studies have proven its accuracy and consistency.
Because of scattering, reflection and interference of the ultrasound beam in myocardial tissue, speckles appear in grey scale two-dimensional (2-D) echographic images. These speckles represent tissue markers that can be tracked from frame to frame throughout the cardiac cycle (see Figure1).
These fingerprints are randomly distributed throughout the myocardium. Each speckle can be identified and tracked by calculating frame to frame changes – similar to analysis with tagged cMR – using a sum of absolute difference algorithms. Motion is analysed by integrating frame to frame changes. Out-of-plane motion occurs due to rotation and motion of the heart into the chest cavity, and may cause the disappearance of the speckles over a few frames, but rarely within two consecutive frames. Philips Tissue Motion Quantification (TMQ) software allows spatial and temporal processing of these markers on 2-D ultrasound images. TMQ speckle tracking also offers an alternative to techniques such as colour-coded tissue Doppler for strain, and strain rate imaging, overcoming many of the problems traditionally associated with angle dependence. A significant advantage consists in the possibility of interrogating radial, circumferential and longitudinal deformation simultaneously from the same acquired loop. By tracking these speckles, the strain, strain rate, tissue velocity and LV rotation can be easily calculated.