Release burst imaging is a method based on the combination of multiple high frequency, broadband-detection pulses with a separate release burst. Release burst imaging is optimally suited to the characteristic of ultrasound contrast agents.
This method allows to improve both contrast sensitivity and imaging resolution. Imaging and transient enhanced scattering can be optimized separately. The release burst mode can be combined with a Doppler method to remove residual clutter signals from moving tissue.

See also Repetition Rate.

The repetition rate is the number of times per second that a probe delivers a sound burst. This rate is equal to the transducer's frequency divided by 1024 or lower as required by ultrasound conditions.

(RI) The resistive index is a measure of resistance to arterial flow and is calculated from the power Doppler arterial waveform.
The equation of this index is:
RI = (peak systolic velocity - end diastolic velocity) : peak systolic velocity

The resolution is the ability to distinguish two adjacent objects or in Doppler measurements the smallest detectable change in flow. Probe resolutions are generally specified at 0.1Hz filtering.

See also Matrix Size.

The resonant frequency is the frequency at which a piezoelectric ceramic (crystal) will vibrate most efficiently. At the resonant frequency the crystal will produce the highest output with the least amount of voltage applied.