Latest Developments in Ultrasound Cardiac Imaging
Latest Developments in Ultrasound Cardiac Imaging
US Cardiology Volume 6 Issue - I
Published: March 2009
Published: March 2009
Abstract
Tissue Doppler echocardiography (TDE) has been used to calculate and display myocardial velocities, strain, or strain rate in various cardiac diseases. Unfortunately, TDE is limited due to angle of incidence dependency, noise, artifacts, tethering, and translation affecting the reproducibility of measurements. 2D speckle tracking echocardiography (2D-STE)—a more robust, angle-independent technique—is able to overcome these limitations and to define radial, circumferential, longitudinal, and transversal strain derived from short- and long-axis planes. 2D-STE has been proved to disclose dyssynchrony not otherwise detected by longitudinal TDE and to offer an insight into rotational mechanics. Recently, 3D-STE based on a pyramidal 3D data set has been introduced, improving information by avoiding loss of speckles. Left ventricular dyssynchrony, determination of volumes, ejection fraction, and any form of myocardial disease are of clinical interest. Myocardial mechanics such as rotation, twist, and torsion can be displayed in 3D to define early-stage myocardial dysfunction, even in patients with normal ejection fraction.
Keywords
Speckle tracking, strain imaging, 3D echocardiography, myocardial mechanics, left ventricular dyssynchrony, ischemic heart disease
Disclosure: The author has no conflicts of interest to declare.
Received: December 1, 2008 Accepted: January 16, 2009
Correspondence: Hans Joachim Nesser, MD, Director, 2nd Department of Medicine, Elisabethinen Teaching Hospital, University of Vienna and Innsbruck, A-4020 Linz, Fadingerstraße, Austria. E: hans-joachim.nesser@elisabethinen.or.at
Tissue Doppler-based measurements of myocardial strain are possible and accurate for structures that move along the ultrasound beam, but are underestimated in other directions and even impossible for angles close to 90º. To overcome these limitations, the speckle tracking technique was introduced in 2004, offering a more user-friendly workflow and better reproducibility.1 This echocardiographic technique is based on frame-by-frame tracking of ultrasound speckles as the natural acoustic markers within the image.
By tracking these speckles at frame rates varying from 40 to 150 frames/s-1, 2D tissue velocity and displacement can be accurately calculated over time, irrespective of the direction of motion. Furthermore, myocardial strain can be determined from the displacement of speckles in relation to each other, providing an angle-independent parameter of regional myocardial function. To obtain this information, the left ventricular myocardium is first traced using the click-to-point approach on the end-systolic frame, followed by automated definition of an epicardial and mid-myocardial line. Whereas apical planes are used to depict longitudinal and transversal strain, the parasternal short-axis views allow the differentiation of circumferential and radial strain. Velocity vector imaging is another technique based on speckle tracking, whereby the vector length depicts the amount of strain and the direction of vectors represents the direction in which tissue is moving.
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