X-Strain Imaging: The Future

X-strain is a new feature now available in echocardiography machines, says V Sukumar.

What is X-Strain

Assessment of myocardial velocities is an emerging non-invasive approach for estimating intrinsic myocardial function, far before an impairment of the pump function, as well as for detecting early impairment of LV diastolic function.

The current standard for evaluating myocardial velocities is represented by Tissue Doppler Imaging (TDI) which is, however, angle-dependent due to use of Doppler effect and also this technique cannot evaluate strain Rate in Radial and circumferential directions. Also this technique is not effective in detection strain in right ventricle and atriums.

X-strain is a new feature now available in echocardiography machines. This technique uses the 2D image of the heart to track and quantify the velocities of the heart segments and thus derives the strain and strain rate involved in the heart more accurately.

With the X-strain technology now the physician can measure not only the longitudinal stress but also the radial and circumferential stress and hence detect the abnormalities of the heart well in advance.

Now with X-strain, which is 2D based technique, one does not have the problem of angle dependence and hence can detect strain and strain rate in any part of the heart such as left ventricle, right ventricle, left atrium, and right atrium.

X- Strain is simple in technology and hence this technique can now be incorporated in medium level machines also and hence ever cardiologist can perform Strain and Strain rate evaluation in all the patients.

The Strain (St), i.e. deformation, is defined as the instantaneous local border lengthening or shortening with respect to one arbitrary instant t0, when L(t0)=L0.

The instant t0 is commonly taken at the end of diastole (ECG R-wave) when the heart muscle is unstressed/unloaded.

St(t)=(L(t)-L0)/L0= l/l0

Therefore, lengthening is represented as a positive value for strain, while shortening is represented by a negative value.

Being the initial instant t0 taken at the end of diastole circumferential and longitudinal Strain Rate (SR) is defined as the modification rate of the Strain (St) over time (t) or, in other words, as the speed at which deformation occurs.

How does X- Strain Works

After myocardial border is manually traced by the operator, an analysis is performed on a pixel by pixel brightness basis allowing the compensation of movements of cardiac segments (translation, lengthening, thickening) and the evaluation of the punctual velocity. The velocity is displayed as a vector overlaid onto the B-mode image where the length of the vector indicates the magnitude of the tissue velocity representation. Several parameters of the heart mechanics may be derived from this velocities such as:

• Strain (Longitudinal and Circumferential).
• Strain Rate (Longitudinal and Circumferential).
• Regional Strain.

Conclusion

Hence now with the availability of X-Strain the cardiologist can detect all the strain and strain rate (longitudinal, radial and circumferential) in any part of the heart and detect the abnormalities being generated in the heart well in advance. This feature is currently being offered in Esaote's MY LAB series Colour Doppler ultrasound scanners.

The writer is Executive Director, Esaote India NS Ltd
E-mail: esaote@airtelbroadband.in