Color Doppler, Tissue Doppler & Multigate Doppler

Tissue Doppler & Multigate Doppler

In the Doppler signal processing chain  , if only large amplitude echoes of lower Doppler frequencies from tissues such as myocardium or heart muscle are retained and low amplitude echoes of higher Doppler frequencies are suppressed, the motion of the tissues can be monitored. This will be touched upon again in the next chapter. An amplitude threshold can be set to allow only the larger echoes to pass through. Tissue Doppler has been proven a clinically useful tool for assessing the state of myocardium. In conventional pulsed Doppler, only one gate is used to measure blood flow within the sampled window or sampling volume confined by the beam width and the gate duration. If blood flow velocities at multiple points along the ultrasound beam need

Doppler Flow Measurements to be measured, pulsed Doppler flow meters with multiple gates (e.g., 8 or 16 gates) have been developed. These devices allow the measurement of velocities in real time across the lumen and thus have been used frequently to determine the blood flow velocity profile in arteries.

Color Doppler

A new way of displaying color Doppler information, i.e., “power mode” or “energy mode” imaging, has been introduced to minimize some of the color Doppler problems (Rubin et al., 1994; Zagzebski, 1996) and has been well accepted by the clinical community. All top-of-the-line scanners now have this option. Instead of the mean Doppler shift, the power contained in the Doppler signal is displayed in this approach. There are several advantages to doing so:

• A threshold can be set to minimize the effect of noise.

• The data can be averaged to achieve a better signal-to-noise ratio.

• The images are less dependent upon the Doppler angle.

• Aliasing is no longer a problem because only the power is detected. As a result, signals from blood flowing in much smaller vessels can be detected. The images so produced have an appearance similar to that of x-ray angiography.