The wall filter is designed to exclude Doppler signals with low frequency, and high amplitude (highpass filter) from moving tissue, such as a vessel wall. Wall filter performance is critical for effectiveness of a color Doppler system.

Tissue-specific ultrasound contrast agents improve the image contrast resolution through differential uptake. The concentration of microbubble contrast agents within the vasculature, reticulo-endothelial, or lymphatic systems produces an effective passive targeting of these areas. Other contrast media concepts include targeted drug delivery via contrast microbubbles.
Tissue-specific ultrasound contrast agents are injected intravenously and taken up by specific tissues or they adhere to specific targets such as venous thrombosis. These effects may require minutes to several hours to reach maximum effectiveness. By enhancing the acoustic differences between normal and diseased tissues, these tissue-specific agents improve the detectability of abnormalities.
Some microbubbles accumulate in normal hepatic tissue; some are phagocytosed by Kupffer cells in the reticuloendothelial system and others may stay in the sinusoids. Liver tumors without normal Kupffer cells can be identified by the lack of the typical mosaic color pattern of the induced acoustic emission. The hepatic parenchymal phase, which may last from less than an hour to several days, depending on the specific contrast medium used, may be imaged by bubble-specific modes such as stimulated acoustic emission (color Doppler using high MI) or pulse inversion imaging.

Ultrasound at the microbubble resonance frequency can cause bubble rupture at high acoustic power (mechanical index (MI) greater than 0.5). The result is a transient high-amplitude, broadband signal containing all frequencies, not only the harmonics. It will create a strong signal in B-mode or a short-lasting multicolored, mosaic-like effect in color Doppler sonography.
Several terms for this typical signal have been used, e.g. induced or stimulated acoustic emission, loss of correlation imaging and sono-scintigraphy.