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Acoustics Today

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Oct 2012

Volume 8, Issue 4, pp. 8-42

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Applications of Transcranial Focused Ultrasound Surgery

Daniel Pajek and Kullervo Hynynen

Acou. Today Volume 8, Issue 4, pp. 8-14 (2012); (7 pages)

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Focused ultrasound is capable of delivering energy into tissue, noninvasively and without the use of ionizing radiation. The ability of focused ultrasound to generate heat in tissue was demonstrated in the brain decades ago, with the creation of lesions in the mammalian central nervous system. A spherically focused ultrasonic transducer causes emitted ultrasound waves to superimpose constructively at a focus, leading to very high energy deposition within a small volume, of a size proportional to the wavelength. Focused ultrasound is an emerging non‐invasive alternative to surgery and an alternative to radiation therapy. This has led to the use of ultrasound in non‐invasive hyperthermia and ablative applications, such as the treatment of uterine fibroids.

Photoacoustic Imaging for Medical Diagnostics

Carolyn L. Bayer, Geoffrey P. Luke, and Stanislav Y. Emelianov

Acou. Today Volume 8, Issue 4, pp. 15-23 (2012); (9 pages)

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Photoacoustic imaging has the potential to provide real‐time, non‐invasive diagnosis of numerous prevalent diseases, due to the technology's unique ability to visualize molecular changes deep within living tissue with spatial resolution comparable to ultrasound. Photoacoustic imaging is a hybrid imaging technique that combines the contrast capabilities and spectral sensitivities of optical imaging with the resolution and tissue penetration capabilities of ultrasound. Today, many in vivo demonstrations of photoacoustic imaging of biomedical applications relevant to medical diagnostics exist, including cancer, brain vasculature and function, cardiovascular, and tissue engineering scaffolds, prompting translational advances in clinical photoacoustic imaging. Because of the potential to perform realtime, non‐invasive in vivo functional and molecular imaging, photoacoustic imaging is increasingly being applied as both a clinical and preclinical method aimed at improving medical diagnostics.

Disintegration of Tissue Using High Intensity Focused Ultrasound: Two Approaches That Utilize Shock Waves

Adam Maxwell, Oleg Sapozhnikov, Michael Bailey, Lawrence Crum, Zhen Xu, Brian Fowlkes, Charles Cain, and Vera Khokhlova

Acou. Today Volume 8, Issue 4, pp. 24-37 (2012); (14 pages)

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Surgery is moving more and more toward minimally‐invasive procedures — using laparoscopic approaches with instruments inserted through tiny incisions or catheters placed in blood vessels through puncture sites. These techniques minimize the risks to the patient such as bleeding complications or infection during surgery. Taken a step further, high‐intensity focused ultrasound (HIFU) can provide a tool to accomplish many of the same procedures without any incision at all. This article discusses the acoustics of histotripsy — including the processes of generation and focusing of intense ultrasound, the formation of cavitation clouds and rapid boiling in tissue, and the interactions of ultrasound shock waves with bubbles leading to tissue disintegration.

Ultrasonic Bioeffects on Peripheral Nerves

Robert Muratore and Jeffrey J. Vaitekunas

Acou. Today Volume 8, Issue 4, pp. 38-42 (2012); (5 pages)

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A century of studies has demonstrated that the nervous system is sensitive to incident ultrasound. A comprehensive review of these effects was published in 2011 by Gavrilov [L.R. Gavrilov and E.M. Tsirulnikov, “Focused ultrasound as a tool to input sensory information in humans (review),” Acoustical Physics 58, 1–21 (2012)]. From his detailed listing of acoustic carrier frequencies, pulse repetition frequencies, intensities, and exposure time, one overarching lesson can be learned: the nervous system responds in some way to nearly any acoustic energy to which it is exposed. The details of specific responses to specific stimuli vary with what the authors of each study were monitoring. In particular, the responses depend on the portion of the nervous system being insonified.
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