Superharmonic imaging uses higher harmonics like third and fourth harmonic to increase the contrast to tissue ratio compared to a second harmonic imaging mode. Second harmonic imaging is better than fundamental imaging, but has limited capabilities to discriminate between tissue and microbubbles, caused by the non-linear propagation of ultrasound.

Targeted ultrasound contrast agents provide advantages compared with usual microbubble blood pool agents. The goal of targeted ultrasound contrast agents is to significantly and selectively enhance the detection of a targeted vascular site. Tissue-specific ultrasound contrast agents improve the image contrast resolution through differential uptake. Targeted drug delivery via contrast microbubbles is another contrast media concept and provides the potential for earlier detection and characterization of disease.
Targeted contrast imaging provides a higher sensitivity and specificity than obtained with a nontargeted contrast agent.
The detection of disease-indicative molecular signatures may allow early assessment of pathology on a molecular level.
Molecular imaging should be an efficient and less invasive technique to obtain three-dimensional localization of pathology.
Ultrasound agents typically remain within the vascular space, and therefore possible targets include molecular markers on thrombus, endothelial cells, and leukocytes. Targeted contrast agents permit noninvasive detection of thrombus, cancer, inflammation, or other sites where specific integrins or other adhesion molecules are expressed. Adhesion molecules such as monoclonal antibodies, peptides, asialoglycoproteins, or polysaccharides are incorporated into the shell of the microbubble or liposome. After injection into the bloodstream, the targeted agent accumulates via adhesion receptors at the affected site, enhancing detection with an ultrasound system.

See also Acoustically Active Lipospheres, and Tissue-Specific Ultrasound Contrast Agent.

The third generation ultrasound contrast agents (UCA/USCA) are more echogenic and stable, and are able to enhance the echogenicity of parenchyma on B-mode images. These microbubbles may thus show perfusion, even in such a difficult region as the myocardium.

See also History of Ultrasound Contrast Agents.

(UCA / USCA) Ultrasonic contrast agents, also called ultrasound contrast agents, are encapsulated bubbles on the order of 1-10 μm in diameter. These gas bubbles are injected into the blood stream in order to increase blood/ tissue contrast during an ultrasonogram. These microbubbles are filled with air or a gas with a lower solubility in blood than air, such as perfluorochemicals. The microbubble shell consists of albumin, phospholipid, or other material and encapsulates the gas core. Due to this construction, ultrasonic contrast agents are highly compressible, and have a high echogenicity.

See also Ultrasound Contrast Agent Safety.

The main advantage of ultrasound is that certain structures can be observed without using radiation. However, ultrasound is energy and there are ultrasound safety regulations, because two bioeffects of ultrasound are heat and cavitation. Ultrasound is a mechanical energy in which a pressure wave travels through tissue. Reflection and scattering back to the transducer are used to form the image. As sound energy is transmitted through the tissue, some energy is reflected and some power is absorbed.
Possible physical effects with ultrasound:
The ultrasound safety is based on two indices, the mechanical index (MI) and the thermal index (TI). The WFUMB guidelines state that ultrasound that produces temperature rises of less than 1.5°C may be used without reservation. They also state that ultrasonic exposure causing temperature rises of greater than 4°C for over 5 min should be considered potentially hazardous. This leaves a wide range of temperature increases which are within the capability of diagnostic ultrasound equipment to produce and for which no time limits are recommended. However, it has not been determined that medical ultrasound causes any adverse reaction or deleterious effect.
The American Institute of Ultrasound in Medicine states that as of 1982, no independently confirmed significant biologic effects had been observed in mammalian tissue below (medical usage) 100mW/cm2.

See also Ultrasound Regulations and Ultrasound Radiation Force.