Ultrasound is most known for its use in OB/Gyn and to a lesser extent as lithotripsy in the treatment of kidney stones. These two applications of ultrasound historically exemplify its safety and power as a surgical tool. Modern ultrasound research and clinical use span a very large range of diseases. The most dominant features of diagnostic ultrasound are the ability to monitor anatomical structures (such as heart, kidney, liver, etc.) and the use of Doppler to visualize blood/fluid flow inside the body in real-time without adverse effects.
State of the art examples of UM-based ultrasound research include a clinical study at the Cancer and Geriatrics Center of the UM-Health System which uses a combination of digital tomosynthesis mammography (DTM) (link is external) and ultrasound for breast cancer detection and imaging. Ultrasound enables the physician to perform tissue palpation without touching the patient. High spatial resolution and large dynamic range ultrasonic imaging yield not only images of anatomical structures in tissue but also quantitative data for tissue elasticity and tissue blood supply, both important indicators for tumor detection and diagnosis. Colocation of ultrasound and DTM allows immediate comparison of apparent tissue abnormalities. The mechanical colocation is supplemented by image fusion/registration (link is external) (developed under Prof. Meyer at UM-Radiology) that allows clinicians to locate, track, and examine selected cysts, masses, or general tissue regions for more spatially detailed evaluation or for comparison of current to past exams. The latter is being investigated for sequential registration of suspicious masses and tumors over time as an assessment of chemotherapy response and is planned for future detection of cancer-like changes in periodic screening. Multi-modality studies such as the above mentioned tomosynthesis-ultrasound system should allow health care practitioners to obtain more effective detection and definitive diagnoses of breast cancer. We continue a rather long history of vascular quantification and elasticity imaging in the breast and elsewhere. Future studies will include a modality called S-PAT (spectral photoacoustic tomography (link is external)). S-PAT itself combines tissue thermal expansion by laser excitation and acoustical readout to assess hemoglobin concentration and its oxygenation. S-PAT is already being studied for arthritis, prostate, and breast imaging with and without nanoparticle contrast agents. Longer term development and application of reconfigurable arrays of tens to hundreds of thousands of ultrasound transducer elements for breast, heart and general applications is progressing with two different companies.
Safety assurance in diagnostic ultrasound is a major goal of our bioeffects research (link is external). The potential for adverse bioeffects o be caused by use of gas microbubble based ultrasound contrast agents is the current subject of study. Research has demonstrated the induction of capillary rupture and effects on adjacent cells in animal models on certain high-exposure modes of contrast ultrasound. Delineation of safe parameter ranges allows the development of guidelines and protocols for assuring the safe use of contrast agents in diagnostic ultrasound.
Ultrasound researchers in Radiology together with scientists in Biomedical Engineering and Urology are developers of and world leaders in histotripsy (link is external), a new application of therapeutic ultrasound. Much like lithotripsy where kidney stones are broken into small fragments, here soft tissue is fragmented to a sub cellular level. This UM research is developing a surgical ultrasound technique that operates in deep tissues with high spatial resolution and no overlying incisions. The body resorbs fragmented tissues and resulting voids are filled by surrounding tissues. Traditional ultrasonic cancer treatment focused on tissue destruction via localized heating/cooking. To the contrary, histotripsy is based on a mechanical disruption, very similar to an actual scalpel. Current and recent studies concentrate on clot dissolution, prostate cancer and atrial-septal penetration, as well as uterine and breast fibroids.
Basic medical research focuses among other projects on the use of perfluorocarbon droplet emulsions. It has been shown that these emulsions can be used in preclinical studies to temporarily obstruct the blood supply in a tissue or organ targeted by focused ultrasound. Exposure to ultrasound induces a vaporization of micrometer sized droplets (link is external) from the fluid phase to the gas phase. Resulting perfluorocarbon gas bubbles are 5-times larger than red blood cells and therefore block capillaries (link is external). Current studies explore the use of this mechanism for a number of therapies. In addition to production of ischemia as a means of therapy, cutting the blood flow to selected regions of the liver or kidney could also be used to enhance the application of radio-frequency ablation. This way droplet vaporization maximizes the effect of radio-frequency ablation by limiting the loss of heat via the blood pool. Moreover, ultrasound vaporization of droplets can deliver drugs to specific body sites such as cancerous masses in the kidney or liver. The incorporation of chemotherapy agents into these small droplets will concentrate the drug release to where the droplets vaporize and simultaneously retain the released drug at this site as the blood flow is stopped. In very low densities, the 30-100 micron gas bubbles can be used as "beacons" to refocus ultrasound beams (link is external) for much improved resolution for diagnosis and therapy, even through difficult tissues such as skull.