Holographic characterization of therapeutic array transducers with assessment of measurement limitations and robustness

• Published in: The Journal of the Acoustical Society of America 2018-09, Vol.144 (3), p.1701-1701
• Main Authors: Kreider, Wayne, Khokhlova, Vera A., Ghanem, Mohamed A., Sapozhnikov, Oleg A.
• Format: Article
• Language: English
• ISSN: 0001-4966; 1520-8524
• DOI: 10.1121/1.5067555

Acoustic holography measurements and corresponding numerical projection methods have recently gained acceptance for characterizing the fields generated by high intensity therapeutic ultrasound (HITU) applications. To facilitate the standardization of such measurement-based simulation methods, it is important to understand how practical measurement challenges and limitations impact the results. Toward this end, holography measurements were acquired and analyzed for characterization of two therapeutic array transducers, each with 256 elements. For different focusing configurations, measurements comprised 2D holography scans as well as 1D scans used to independently quantify the focal lobe. The fields projected from holograms were compared to independent 1D scans to evaluate the impacts of hydrophone directivity, non-orthogonality of the axes of the positioner used to move the hydrophone, and overall mechanical stability of measurements. Results demonstrate that directivity effects exceeded those expected based on hydrophone size and altered focal pressures on the order of 10%. Non-orthogonality of the positioner shifted apparent focal locations by measurable distances, which could be confused with small shifts in device fixturing. However, holographic reconstruction of the ultrasound field structure near the focal lobe was robust with respect to directivity and non-orthogonality, which enables compensation by relative calibration of source output levels. [Funding support by NIH R01-EB025187, R01-EB007643, and P01-DK043881.]