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Phase aberration induced by soft tissue inhomogeneities often complicates high-intensity focused ultrasound (HIFU) therapies by distorting the field and, previously, we designed and fabricated a bilayer gel phantom to reproducibly mimic that effect. A surface pattern containing size scales relevant to inhomogeneities of a porcine body wall was introduced between gel materials with fat- and muscle-like acoustic properties—ballistic and polyvinyl alcohol gels. Here, the phantom design was refined to achieve relevant values of ultrasound absorption and scattering and make it more robust, facilitating frequent handling and use in various experimental arrangements. The fidelity of the interfacial surface of the fabricated phantom to the design was confirmed by three-dimensional ultrasound imaging. The HIFU field distortions—displacement of the focus, enlargement of the focal region, and reduction of focal pressure—produced by the phantom were characterized using hydrophone measurements with a 1.5 MHz 256-element HIFU array and found to be similar to those induced by an ex vivo porcine body wall. A phase correction approach was used to mitigate the aberration effect on nonlinear focal waveforms and enable boiling histotripsy treatments through the phantom or body wall. The refined phantom represents a practical tool to explore HIFU therapy systems capabilities.

Aberrations induced by soft tissue inhomogeneities distort acoustic fields and often complicate HIFU therapies. An aberration-generating phantom was designed and fabricated to mimic the acoustic effects of a porcine body wall. A rippled surface pattern replicating inhomogeneities of size scales relevant to the porcine body wall was transferred to a large phantom made of fat-like and muscle-like gel materials. The acoustic distortions produced by the phantom and an ex vivo porcine body wall were characterized by hydrophone measurements with a 256-element 1.5 MHz focused ultrasound array (diameter = 144 mm, F# = 0.83). Insertion of the phantom generated large distortions for both linear and nonlinear beam focusing including displacement of the focus (up to 0.3 mm transversely), enlargement of the focal region, and reduction in focal pressures due to aberration (up to 2.5-fold peak positive pressure reduction). The phantom and porcine body wall produced similar levels of aberration and attenuation effects. An aberration correction approach was leveraged to isolate the quantitative effect of aberration and to restore shocks in nonlinear waveforms in the focus. Boiling histotripsy treatments through the phantom or body wall were subsequently demonstrated in a hematoma sample. [This work was supported by NIH R01EB7643 and R01EB25187, and RSF 20-12-00145.]

The assumptions of geometric shape and uniform velocity profile prohibit the use of conventional Doppler methods for volume flow quantification with irregularly shaped nonvascular passages in space. A flow quantification method that integrates a three‐dimensional (3‐D) position and orientation sensing system with digital color Doppler imaging approach has been developed. Methods: The optimized ultrasound system settings were predetermined using a static, laminar flow model. The instantaneous flow rate was measured by the integration of the area‐velocity product with angle correction. Initial in vivo studies quantified gastric emptying on five healthy volunteers 10 min after ingestion of a 500‐ml meat soup, postprandially. Digital Doppler images were obtained continuously covering a transpyloric flow episode, immediately following the 3‐D scan of the passage. The flow direction was derived from 3‐D reconstruction using the centroids of two short‐axis views. Results: In vitro validation showed the Doppler flow rates were within 10% for reference flow rates ranging from 6 to 30 ml/s. The average gastric emptying lasted 0.75 s with 3.0 ml in volume. Conclusions: With appropriate instrument settings, orientation determined digital Doppler can be used for the quantification of gastric emptying with adequate accuracy. This method minimized the angular ambiguity and geometric assumptions.

At the 105th ASA meeting we presented results of our research on the Tadoma method of tactile speech reception and described our ongoing development of a “synthetic Tadoma system” for use as a research tool in studying transformations of Tadoma [Reed et al., J. Acoust. Soc. Am. Suppl. 1 73, S26 (1983)]. In the synthetic Tadoma system, signals recorded from a talker's face are used to control an artificial mechanical face. Preliminary evaluation of the system has involved roving ABX discrimination tests among sets of 15 vowels in CVC contexts and among sets of 24 consonants in CV contexts. Two naive adult subjects, with simulated deafness and blindness, have been tested. Average results for vowel discrimination (68%) were equal to those obtained in a comparable study of natural Tadoma [Reed et al., J. Speech Hear. Res. 21, 625–637 (1978)]. Results for consonant discrimination were lower for the synthetic system (68% vs 78%), but were improved (to 74%) following certain modifications to the system. [Work supported by NSF.]