Page 59 - 2016Winter

sues, giving clinicians new diagnostic information. The use of novel imaging methods with ultrasound contrast agents, e.g., preformed, shelled microbubbles that are injected intra- venously, is also studied by several BATC members. In par- ticular, novel uses of the inherent nonlinear response of mi- crobubbles to acoustic waves are an evolving research topic.
The therapeutic use of ultrasound is another major area be- ing explored by many BATC members. These devices focus high-intensity ultrasound into soft tissue to induce biologi- cal effects that arise from heating or mechanical effects that are primarily related to cavitation. Although this use of ul- trasound has been investigated for more than 60 years, im- provements in medical imaging have led to increased inter- est and visibility of this noninvasive technology in the last decade. It is a rapidly growing field, with several companies that have developed devices to treat practically every part of the body. Beyond the ASA, the field now supports an in- ternational society and an active nonprofit foundation (the Focused Ultrasound Surgery Foundation) that both hold well-attended meetings, with attendance that is growing ev- ery year.
Currently approved treatments use focused ultrasound to thermally ablate tumors or other tissues as alternatives to surgery or ionizing radiation. In the United States, treat- ments that ablate prostate tissue, uterine fibroids, and bone metastases are now approved for commercial use. In July 2016, ablation of a target in the brain to treat essential tremor was approved by the Food and Drug Administration. Multiple other treatments are currently being tested clini- cally with focused ultrasound ablation, including treatments for cancer in the breast, pancreas, and brain. The reader is pointed to the Web site of the Focused Ultrasound Surgery Foundation (www.fusfoundation.org) that has compiled an
extensive list of hundreds of different applications of thera- peutic ultrasound.
A new range of treatments is emerging that uses cavitation, the interaction of microbubbles and the acoustic field. These microbubbles can be created from gas nuclei present in tis- sues or are introduced systemically with the administration of microbubble-based ultrasound contrast agents. Because, unlike fluids, gas is strongly compressible, these microbub- bles have an outsized response to even moderate acoustic intensities and can be used to enhance ultrasound therapies and to produce completely new applications. A particularly promising application of cavitation is the use of short ultra- sound bursts at pressure amplitudes exceeding 10 MPa to disintegrate tissue. This treatment, termed “histotripsy,” of- fers a significant reduction in treatment time, a current is- sue with thermal ablation, and improves the ability of using ultrasound imaging to monitor the procedure (e.g., Xu et al., 2007). Recent work has explored pressure amplitudes above the intrinsic threshold of water to induce cavitation with a single acoustic cycle. This approach leads to highly repro- ducible cavitation generation on a submillimeter scale (e.g., Vlaisavljevich et al., 2015).
Another exciting area in therapeutic ultrasound is the use of microbubbles or heat to enhance or trigger the delivery of therapeutic agents in the body (Kooiman et al., 2014). These approaches can direct the delivery of therapeutic agents to only the desired tissue targets or they can enable drugs to be delivered where they are currently restricted, such as in many tumors or in the central nervous system. Two ap- proaches are used for ultrasound-induced drug delivery. One approach uses ultrasound to modify cellular membranes or vascular permeability to facilitate drug penetration. “Sono- poration,” an alternative to the better known electropora-
Variable acoustics including low frequencies
Bass frequency control is crucial for amplified music concerts Mobile solution available: aQtube®
aQflexTM : Revolutionary on/off sound absorption system
Lowers RT (63 – 1000 Hz) by up to 45% at the push of a button
aon = app. 0.5 (63 – 1000 Hz) in entire ceiling area. aoff = app. 0.0 Obtain sought-after low frequency control
For music education, multipurpose concert halls, theatres etc.
Complies with safety and fire regulations (B,s1 – d0 standard)
Projects in Dubai, Germany, Finland, Denmark, Kuwait, Norway etc. Patents: EP 1 779375 B1, JP 2008 510408, US 7905323 etc.
Engineered by Gerriets Germany
For more information please visit our website: www.flexac.com
Winter 2016 | Acoustics Today | 57