Clutters are unwanted components of the received signal. In contrast enhanced ultrasound, clutter often describes the part of the received echo that is not from microbubble contrast agents.

See also Release Burst Imaging.

A filter in electronics is a circuit that only passes certain signals. In ultrasound is a filter a device to suppress acoustic or electromagnetic waves of certain frequencies, letting other frequencies pass, e.g. high pass filter, low pass filter. The high pass filter is the wall filter (also called thump filter) used in Doppler devices to eliminate low frequency Doppler shifts caused by clutter. For blood flow measurement, a low pass filter is often used to strip out high frequency noise, leaving only the biological components of interest. Frame averaging is a form of a low pass filter.

Blood volume per time measured in: cm³/s.
The sonographic detection of blood flow in vascular ultrasound is limited by factors such as tissue motion (clutter), attenuation properties of the intervening tissue, and slow or low-volume flow.

Different flow types in human body:

See also Antegrade, Bi-directional Flow, Velocity, Poiseulles Law, and Venous Ultrasound.

(HPD) Harmonic power Doppler is currently one of the most sensitive techniques for detecting ultrasound contrast agents. HPD works by transmitting multiple pulses toward the object to be imaged and detecting the pulse-to-pulse changes in the received echo signals.
Second harmonic bandbass filtering is applied to the received signals to exploit the non-linear behavior of scattering from bubbles (clutter). Harmonic power Doppler operates best at high output levels because of increased contrast destruction, and pulse amplitudes close to the maximum allowed are used much of the time.
With a high mechanical index, non-linear propagation of the sound will cause significant harmonic components from tissue, and the contrast agent to tissue ratio will decrease.
Also called Harmonic Power Angio. See also Multiple Frame Trigger.

(MCE) Myocardial contrast echocardiography is a contrast enhanced ultrasound method that utilizes intravenous injected microbubbles as red blood cell tracers. MCE can assess myocardial perfusion both at rest and stress to evaluate viable myocardium after acute infarction.
MCE perfusion imaging improves the blood echoes during the microbubble passage and the imaging system suppresses the clutter represented by non-contrast-bearing tissue.

See also Injection Rate, Stress Echocardiogram, and Myomap.