(ESWL) Extracorporeal shock wave lithotripsy is a special use of kidney ultrasound, where high intensity focused ultrasound pulses are used to break up calcified stones in the kidney, bladder, or urethra. Pulses of sonic waves pulverize dense renal stones, which are then more easily passed through the ureter and out of the body in the urine. The ultrasound energy at high acoustic power levels is focused to a point exactly on the stone requiring an ultrasound scanning gel for maximum acoustic transmission.
Air bubbles in the ultrasound couplant, regardless of their size, degrade the performance of Lithotripsy and have the following effect:
Air bubbles smaller that 1/4 wavelength cause scattering of the sound waves as omni directional scatterers and less acoustic energy reaches the focal point. The result is less acoustic power at the focal point to disintegrate the kidney stone.
Air bubbles larger than 1/4 wavelength act as reflectors and deflects the acoustic energy off in a different direction. These results in less acoustic energy at the focal point.
Microbubbles dispersed throughout the ultrasound couplant layer change the average acoustic impedance of the gel layer (which reduces the total transmitted energy) and, due to refraction, change the focal point.

From Mallinckrodt Inc
MP1950 is an experimental thin lipid-shelled ultrasound contrast agent with a decafluorobutane gas core. MP1950 has a monolayer lipid microbubble shell with a thickness in the order of a few nanometers.

MRX 115 is a liposome based microbubble formulation and has been demonstrated as effective for cardiac blood pool imaging, Doppler enhancement and potentially myocardial perfusion imaging.
MRX 115 is based upon the demand for a stable, robust blood pool ultrasound contrast agents, also called DMP 115 or Aerosomes™ (ImaRx LLC) and now Definity®.

A negative bolus is created after microbubble destruction at a specific location by the absence of bubbles.

Non-linear scattering describes in physics the conversion of a photon from one wavelength to one or more other wavelengths. In ultrasound, non-linear scattering is the generation of an echo containing higher harmonics. In the case of a microbubble, the oscillation is asymmetric with time, producing echoes with even harmonics.

See also Cross-section Scattering.