Perivascular is the region around (surrounding) vessels.

The persistence of microbubbles is depended of the shell stability and the density of the gas.
This is defined by the equation:
(R x d)/(DIFS x const_sat)
where R is the bubble radius, d the gas density, DIFS the gas diffusivity and const_sat the saturation constant.
Microbubbles are stabilized with thin coatings of substances such as palmitic acid or by encapsulation in microspheres made with albumin, lipids, or polymers. Low-solubility low-diffusibility gases dramatically improve the persistence. Most recently developed ultrasound contrast agents combine these two approaches to prolong contrast enhancement.
Persistence is also a type of temporal smoothing used in both gray scale and color Doppler imaging. Successive frames are averaged as they are displayed to reduce the variations in the image between frames, hence lowering the temporal resolution of the image.

(Perfluorocarbon exposed sonicated dextrose albumin) PESDA are sonicated dextrose albumin microbubbles containing decafluorobutane gas. PESDA is a sonicated self made contrast agent and not a commercial product.
PESDA microbubbles can be used as a blood pool contrast agent in echocardiography to improve the detection of myocardial perfusion abnormalities.

Different stages of testing drugs in humans for example ultrasound contrast agents, from first application in humans through limited and broad clinical tests, to postmarketing studies. Preclinical trials are the testing in animals.

See also Drug Development and Approval Process USA, Food and Drug Administration, and European Medicines Agency.

Phase in ultrasound describes where the sound wave is in its cycle of amplitude change. Different waves oscillate at different frequencies, so time is often not a suitable measure of phase.
The phase shift is a difference in the phase or the temporal offset of the peaks of a waveform along one scan line.

See also Coherence, and Histogram.