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Focused Ultrasounds and Their Applications in Medicine

Reporter: Danut Dragoi, PhD

Any waves focused in a point of material that support their propagation produce heating effects that are useful in medical applications.

Doctors in Los Angeles applied this heating principle for acoustic waves. They use high intensity focused ultrasounds to kill certain cancer tumors that allows the patient to go home on the same day. Surgeons at the Keck Medical Center of the University of Southern California became the first doctors to use this procedure on a patient with the help of high intensity focused ultrasound, or HIFU, and new robotic technology.

The principle of focused wave is not new, but the technology to apply it is. In many places of the world the research on ultrasound applications is producing important results. Doctors from Europe imported equipment to apply this technique. An excellent review and description of how HIFU technique is working given here .

We need to highlight that the temperature increases exponentially with the distance close to the focus point inside the human body where instantaneous protein destruction occurs. As remarked in the review paper mentioned in the previous link the various methods of focusing ultra sound (US) waves have been another important issue.

The simplest and cheapest (often most accurate) method may be a self-focusing, for instance, a spherically curved US source (transducer). An US transducer constructed according to this method, has a beam focus fixed at the position determined from the geometrical specifications of the transducer. To compensate for its lack of versatility, a flat US transducer with an interchangeable acoustic lens system was devised. The acoustic lens enables variation of focusing properties such as focal length and focal geometry. However, a drawback of the lens system is that US waves undergo sonic attenuation and the sonic signal has to be guided  due to absorption by the lens.

Recently, a phased array US transducer technique was adopted for HIFU therapy. By sending temporally different sets of electronic signals to each specific transducer component, this technique enables beam steering and focusing, which can move a focal spot in virtually any direction within physically allowed ranges.

HIFU clinical applications are listed here. Among important clinical applications, there are listed:

• prostate tumors: with several devices under ultrasonic guidance and commercially available as (Ablatherm®, Sonablate ®), Fibroids with MRgHIFU procedures and available as Exablate ® (Insightec + GE)-
• FDA 2004 and Philips CE approved Dec 2009, breast cancer on clinical research, bone tumors on clinical research, brain on small clinical studies with limitation: skull (bone) acoustic interface and no motion,
• liver using Haifu® under ultrasonic guidance MRgHIFU procedures: small clinical studies with limitation on aeric and bone interfaces and motions.

From technological point of view, the most important element of a HIFU is the piezoelectric transducer that takes an alternative voltage of high frequency and convert the electrical energy into acoustic energy.

The physics of generation of ultrasounds is shown in the link here. The electronic circuits behind the HIFU devices is refined over a period of about two decades reaching today with commercial devices available not only for research but also for private clinics around the world.

The precision of focusing the acoustic power into a small region of the human soft tissue depends on the working distance of the HFU device as well as high accuracy of controlling the image of the targeted area. Successes of this technology is reported in here.

SOURCE

http://www.voanews.com/content/high-intensity-focused-ultrasound-used-to-kill-cancer-tumor/2459185.html