Tissue Doppler imaging

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Traditionally, regional left ventricular function by echocardiography has been evaluated visually. Visual assessment is subjective and more accurate and objective methods are needed. As opposed from CMR studies, where calculation of ejection fraction (EF) is obligatory, accurate evaluation of EF using Simpson's formula, has been performed only in selected echocardiographic exams. Regional LV function has always been assessed visually.

Tissue Doppler Imaging

With the development of echo techniques and better delineation of endocardial borders, more advanced echo methods became available. Integrated backscatter was the first technique for regional assessment of LV contraction.[1] Further technological development allowed measurement of myocardial as opposed to intra-cavitary velocities.[2][3] Tissue Doppler Imaging permits accurate calculation of myocardial velocities and deformation parameters: strain and strain rate. Estimation of myocardial velocities with Tissue Doppler is based on the principles of traditional pulsed-wave and color Doppler echocardiography. A high-pass wall filter is used to measure blood flow velocities, and a low pass filter is used to estimate tissue velocities.[4]

Strain is the fractional change in the length of a myocardial segment, and is usually expressed as percentage. It may have positive and negative values which reflect lengthening or shortening.

Strain rate, SR, is the rate of change in strain and is usually expressed as 1/sec or sec-1. Deformation parameters: velocities, strain and strain rate can be assessed along the x, y and z directions, or along the anatomical coordinates of the left ventricle: longitudinal, radial and circumferential. Global strain reflects average longitudinal or circumferential strain over the left ventricle.[4]

Acquisition of the images should be performed with frame rate more than 100 frames /s, angle ≤15° and usually from the apical views.[4] Assessment of deformation parameters with Doppler Tissue Imaging can be affected by global heart motion and breathing, it is angle dependent and is best performed from apical views.

Today, Doppler Tissue Imaging is used mainly for the measurements of mitral annular velocities and is essential for the evaluation of diastolic function.

Additional application of Doppler Tissue Imaging – evaluation of mechanical dyssynchrony before cardiac resynchronization therapy (CRT) may be used in borderline cases.

Tissue velocities in the basal and mid-ventricular segments in the patient scheduled for CRT

References

  1. Vered Z, Mohr GA, Barzilai B, Gesler C, Wickline S, Wear K, et al. Ultrasound integrated backscatter tissue characterization of remote myocardial infarction in human subjects. J Am Coll Cardiol 1989;13:84-91.
  2. Sutherland GR, Stewart MJ, Groundstroem KW, Moran CM, Fleming A, Guell-Peris FJ, et al. Color Doppler myocardial imaging: a new technique for the assessment of myocardial function. J Am Soc Echocardiogr 1994;7:441-58.
  3. Heidmal A, Stoylen A, Torp H, Skjaerpe T. Real-time strain rate imaging of the left ventricle by ultrasound. J Am Soc Echocardiogr 1998;11:1013-9.
  4. 4.0 4.1 4.2 Mor-Avi, et al. Current and Evolving Echocardiographic Techniques for the Quantitative Evaluation of Cardiac Mechanics: ASE/EAE Consensus Statement on Methodology and Indications J Am Soc Echocardiogr 2011;24:277-313.
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