Speckle Tracking

Technology & Services Section

Speckle Tracking Echocardiography

a report by

C é l i n e G o f f i n e t , M D and J e a n - L o u i s V a n o v e r s c h e l d e , M D , P h D
Philips

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 deformationindependently 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 timeconsumingand 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 myocardialtissue, 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). Figure 1: Speckle Tracking Pattern

speckle tracking also offers an alternative to techniques such as colourcoded tissue Doppler for strain, and strain rate imaging, overcoming many of theproblems 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. Clinical Applications Myocardial Strain Measurement 2-D echocardiographyis currently the first-line imaging modality for assessing global and regional function. Using 2-D echocardiography, LV function is most often evaluated visually. 2-D echocardiography also offers the opportunity to measure end diastolic and end systolic volumes, by use of a modified Simpson rule, and thereby to calculate LV ejection fraction. Myocardial thickening and segmental wall motion canalso be assessed, although these measures are even harder to assess, and are therefore most often visually estimated on the 2-D ultrasound images. This qualitative approach suffers obvious limitations. Its accuracy, depends on the expertise of the reader, resulting in large intra- and interobserver variabilities. Furthermore, it estimates only radial deformations of the myocardium, whereas others –such as thickening, shortening and twisting – are ignored. Recently, strain and strain rate imaging – using colour-coded tissue Doppler imaging – have emerged as a quantitative technique to estimate myocardial function and contractility, and the clinical utility of these measurements has been demonstrated in numerous studies.1-8 However, analysis of myocardial strain by tissue Doppler is restrictedalong the axis parallel to the ultrasound beam, and is thus limited by this angle dependence. By analysing speckle motion, STE offers the opportunity to assess myocardial tissue velocity, strain and strain rate independently of cardiac translation and beam angle. STE is simple to perform, it requires only one cardiac cycle, and further processing and interpretation can be done offline. Thesoftware only requires harmonic and high frame rate imaging (see Figure 2).

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...