Tissue Doppler imaging (echocardiography)

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A variant of pulsed wave Doppler, tissue Doppler imaging (TDI) is a modality in echocardiography that allows measurement of the velocity of myocardial movement throughout the cardiac cycle.

Physics

Color flow, pulsed wave, and continuous wave Doppler are designed to analyze the Doppler shifts corresponding to cardiac blood flow, and typically operates on a measurement scale using meters per second (m/s). Cardiac structures, however, move at significantly slower velocities, measured on a scale of centimeters per second (cm/s), with peak tissue velocities rarely exceeding 20 cm/s. This renders them invisible to most other spectral Doppler modalities which filter out such low velocities. The high amplitude of tissue movement (compared to blood flow) further compounds this problem, which is addressed by the following features of tissue Doppler ;

  • removal of the "high pass filter"
    • important for other spectral Doppler modalities to filter out lower velocities (irrespective of signal amplitude)
    • almost entirely removed in tissue Doppler imaging 
  • reduction of gain amplification
    • filters out the significantly lower amplitude Doppler shifts produced by blood flow
    • application of a "low pass filter," which eliminates higher velocities, further enhances visualization of tissue excursion

Radiographic features

Tissue Doppler imaging has two variants which are used to assess cardiac performance in slightly different contexts.

Color tissue Doppler imaging

As with color flow Doppler (CFD), the color map in this variant of TDI allows comparison of regional velocity and direction, albeit at the expense of the quantification provided by pulsed wave Doppler (PWD). Its primary application is in the assessment of myocardial contraction homogeneity, particularly pertinent in the following pathological entities;

  • left ventricular aneurysm
    • dyskinetic wall motion will have an opposite color code to the normally contractile segments of myocardium
  • myocardial ischemia 
    • reduction of endocardial excursion velocity and wall thickening occur early in the ischemic cascade
      • normally contractile myocardium will appear brighter compared to the hypo/akinetic ischemic segments

​Pulsed wave TDI, discussed below, may be used simultaneously for precise velocity quantification in a region of interest.

Pulsed wave tissue Doppler imaging

Performed in a similar manner to conventional PWD, this modality allows precise velocity quantification of tissue within a region of interest designated by the pulsed wave "sample volume" (or "gate"). Its primary use is in the echocardiographic assessment of diastolic function, in which a pulsed wave sample volume is placed adjacent to the (septal or lateral) mitral annulus yielding a waveform with three inflections corresponding to the following events in the cardiac cycle ;

  • mitral annular early diastolic velocity (e')
    • ascent of the mitral annulus from the cardiac apex to the base in early diastole
      • corresponds with the onset of early rapid filling of the left ventricle
      • strongly associated with the experimentally defined time constant of left ventricular relaxation
    • referred to as "Ea" or, more commonly, the "e' velocity"
  • late diastolic atrial contraction velocity (a')
    • referred to as "Ea" or the a' velocity
    • occurs in the same direction as the e' wave
  • longitudinal systolic velocity (s’)
    • systolic descent of the mitral annulus toward the cardiac apex

Assessment of diastolic function with tissue Doppler imaging offers measures which are more independent of preload than conventional PWD . The two modalities are often combined to calculate left ventricular filling pressures.

Practical points