ABSTRACT:
Ultrasound contrast agents are highly echogenic micro bubbles with many unique properties. Micro bubbles can basically improve the sensitivity of conventional ultrasound imaging to the microcirculation. The resonance of micro bubbles in response to an incident ultrasound pulse results in nonlinear harmonic emission that serves as the signature of micro bubbles in micro bubble-specific imaging. Inertial cavitations and destruction of micro bubbles can produce a strong mechanical stress enhancing the permeability of the surrounding tissues, and can further increase the extravasations of drugs from the blood into the cytoplasm or interstitium. Stable cavitations by high-frequency ultrasound can also mildly increase tissue permeability without causing any damage even at a high acoustic pressure. It is cheap, widely available and portable. Using Doppler methods, flow information can be obtained easily and non-invasively. It is arguably the most physiological modality, able to image structure and function with less sedation than other modalities. This means that function is minimally disturbed, and multiple repeat studies or the effect of interventions can easily be assessed. Ultrasound is also unique in being both an imaging and therapeutic tool and its value in gene therapy has received much recent interest. Ultrasound biomicroscopy has been used for in utero imaging and can guide injection of virus and cells. Ultra high frequency ultrasound can be used to determine cell mechanical properties. The development of micro bubble contrast agents has opened many new opportunities, including new functional imaging methods, the ability to image capillary flow and the possibility of molecular targeting using labeled micro bubbles.