High-intensity focused ultrasound (HIFU) is a rapidly developing medical technology that relies on focusing acoustic waves to treat remote tissue sites inside the body without damaging intervening tissues. HIFU can be used to treat benign and malignant tumors, dissolve blood clots, enhance drug delivery to specific sites, and ablate brain tissue causing essential tremors. While standard practices for characterizing diagnostic ultrasound are well established, the lack of analogous metrology techniques for therapeutic ultrasound remains an impediment to broader clinical acceptance of HIFU.

Because ultrasound consists of waves, it possesses several basic features of wave physics that are of practical utility. In particular, it is possible to reproduce a three-dimensional field from a two-dimensional distribution of the wave amplitude and phase along some surface transverse to the wave propagation. This principle is widely used in optics, and the cor res ponding process is termed “holography.” A similar approach is possible in acoustics. For acoustic pressure waves, amplitude and phase can often be measured directly with a pressure sensor, and a two-dimensional distribution of such measurements represents a hologram.

The present technology relates to portable acoustic holography systems for therapeutic ultrasound sources, and associated devices and methods. A method of characterizing an ultrasound source by acoustic holography includes the use of a transducer geometry characteristic, a transducer operation characteristic, and a holography system measurement characteristic. A control computer can be instructed to determine holography measurement parameters. Based on the holography measurement parameters, the method can include scanning a target surface to obtain a hologram. Waveform measurements at a plurality of points on the target surface can be captured. Finally, the method can include processing the measurements to reconstruct at least one characteristic of the ultrasound source.

The system can include an input device capable of receiving inputs related to system components and/or operational characteristics. Inputs related to the measurement apparatus can include, for example, the size of a hydrophone sensing region, a hydrophone bandwidth, a geometry of a test tank and associated fixturing, a liquid temperature in a test tank, and a reference position relative to a transducer at which a hydrophone is initially located. These can be received as user inputs from a storage source (e.g., a database) or directly from system components.

The algorithm can utilize numerical and/or experimental studies of amplitude and phase distributions of acoustic fields radiated by representative clinical therapeutic ultrasound sources. Hologram measurements can be recorded, and subsequent analysis and calculations can be performed. The control computer can thus identify standard parameters for a given arrangement of a holography system.

A signal processor can receive the acoustic waveform data from the data recorder and perform signal processing on the data in order to define and output a measured hologram from the raw measurements. Based on the measured hologram, the system can utilize a control computer to generate one or more characteristics of an ultrasound source. A series of holograms recorded over a range of output levels can be used to fully characterize source output levels.

This work was done by Oleg Sapozhnikov, Michael Bailey, Peter Kaczkowski, Vera Khokhlova, and Wayne Kreider of the University of Washington for Johnson Space Center. NASA is seeking partners to further develop this technology through joint cooperative research and development. For more information about this technology and to explore opportunities, please contact This email address is being protected from spambots. You need JavaScript enabled to view it.. MSC-26064-1


NASA Tech Briefs Magazine

This article first appeared in the July, 2016 issue of NASA Tech Briefs Magazine.

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