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Christopher Hunter

Ultrasound Engineer






B.S. Applied and Computational Mathematical Sciences, University of Washington, 2015


2000-present and while at APL-UW

A prototype therapy system for boiling histotripsy in abdominal targets based on a 256-element spiral array

Bawiec, C.R., T.D. Khokhlova, O.A Sapozhnikov, P.B. Rosnitskiy, B.W. Cunitz, M.A. Ghanem, C. Hunter, W. Kreider, G.R. Schade, P.V. Yuldashev, and V.A. Khokhlova, "A prototype therapy system for boiling histotripsy in abdominal targets based on a 256-element spiral array," IEEE Trans. Ultrason. Ferroelectr. Freq. Control, 68, 1496-1510, doi:10.1109/TUFFC.2020.3036580, 2021.

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1 May 2021

Boiling histotripsy (BH) uses millisecond-long ultrasound (US) pulses with high-amplitude shocks to mechanically fractionate tissue with potential for real-time lesion monitoring by US imaging. For BH treatments of abdominal organs, a high-power multielement phased array system capable of electronic focus steering and aberration correction for body wall inhomogeneities is needed. In this work, a preclinical BH system was built comprising a custom 256-element 1.5-MHz phased array (Imasonic, Besançon, France) with a central opening for mounting an imaging probe. The array was electronically matched to a Verasonics research US system with a 1.2-kW external power source. Driving electronics and software of the system were modified to provide a pulse average acoustic power of 2.2 kW sustained for 10 ms with a 1–2-Hz repetition rate for delivering BH exposures. System performance was characterized by hydrophone measurements in water combined with nonlinear wave simulations based on the Westervelt equation. Fully developed shocks of 100-MPa amplitude are formed at the focus at 275-W acoustic power. Electronic steering capabilities of the array were evaluated for shock-producing conditions to determine power compensation strategies that equalize BH exposures at multiple focal locations across the planned treatment volume. The system was used to produce continuous volumetric BH lesions in ex vivo bovine liver with 1-mm focus spacing, 10-ms pulselength, five pulses/focus, and 1% duty cycle.

Bilayer aberration-inducing gel phantom for high intensity focused ultrasound applications

Peek, A.T., C. Hunter, W. Kreider, T.D. Khokhlova, P.B. Rosnitskiy, P.V. Yuldashev, O.A. Sapozhnikov, and V.A. Khokhlova, "Bilayer aberration-inducing gel phantom for high intensity focused ultrasound applications," J. Acoust. Soc. Am., 148, 3569-3580, doi:10.1121/10.0002877, 2020.

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1 Dec 2020

Aberrations induced by soft tissue inhomogeneities often complicate high-intensity focused ultrasound (HIFU) therapies. In this work, a bilayer phantom made from polyvinyl alcohol hydrogel and ballistic gel was built to mimic alternating layers of water-based and lipid tissues characteristic of an abdominal body wall and to reproducibly distort HIFU fields. The density, sound speed, and attenuation coefficient of each material were measured using a homogeneous gel layer. A surface with random topographical features was designed as an interface between gel layers using a 2D Fourier spectrum approach and replicating different spatial scales of tissue inhomogeneities. Distortion of the field of a 256-element 1.5 MHz HIFU array by the phantom was characterized through hydrophone measurements for linear and nonlinear beam focusing and compared to the corresponding distortion induced by an ex vivo porcine body wall of the same thickness. Both spatial shift and widening of the focal lobe were observed, as well as dramatic reduction in focal pressures caused by aberrations. The results suggest that the phantom produced levels of aberration that are similar to a real body wall and can serve as a research tool for studying HIFU effects as well as for developing algorithms for aberration correction.

Effect of stiffness of large extravascular hematomas on their susceptibility to boiling histotripsy liquefaction in vitro

Khokhlova, T.D., J.C. Kucewicz, E.M. Ponomarchuk, C. Hunter, M. Bruce, V.A. Khokhlova, T.J. Matula, and W. Monsky, "Effect of stiffness of large extravascular hematomas on their susceptibility to boiling histotripsy liquefaction in vitro," Ultrasound Med. Biol., 46, 2007-2016, doi:10.1016/j.ultrasmedbio.2020.04.023, 2020.

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1 Aug 2020

Large intra-abdominal, retroperitoneal and intramuscular hematomas are common consequences of sharp and blunt trauma and post-surgical bleeds, and often threaten organ failure, compartment syndrome or spontaneous infection. Current therapy options include surgical evacuation and placement of indwelling drains that are not effective because of the viscosity of the organized hematoma. We have previously reported the feasibility of using boiling histotripsy (BH) — a pulsed high-intensity focused ultrasound method — for liquefaction of large volumes of freshly coagulated blood and subsequent fine-needle aspiration. The goal of this work was to evaluate the changes in stiffness of large coagulated blood volumes with aging and retraction in vitro, and to correlate these changes with the size of the BH void and, therefore, the susceptibility of the material to BH liquefaction. Large-volume (55–200 mL) whole-blood clots were fabricated in plastic molds from human and bovine blood, either by natural clotting or by recalcification of anticoagulated blood, with or without addition of thrombin. Retraction of the clots was achieved by incubation for 3 h, 3 d or 8 d. The shear modulus of the samples was measured with a custom-built indentometer and shear wave elasticity (SWE) imaging. Sizes of single liquefied lesions produced with a 1.5-MHz high-intensity focused ultrasound transducer within a 30-s standard BH exposure served as the metric for susceptibility of clot material to this treatment. Neither the shear moduli of naturally clotted human samples (0.52 ± 0.08 kPa), nor their degree of retraction (ratio of expelled fluid to original volume 50%––58%) depended on the length of incubation within 0–8 d, and were significantly lower than those of bovine samples (2.85 ± 0.17 kPa, retraction 5%–38%). In clots made from anticoagulated bovine blood, the variation of calcium chloride concentration within 5––40 mmol/L did not change the stiffness, whereas lower concentrations and the addition of thrombin resulted in significantly softer clots, similar to naturally clotted human samples. Within the achievable shear modulus range (0.4–1.6 kPa), the width of the BH-liquefied lesion was more affected by the changes in stiffness than the length of the lesion. In all cases, however, the lesions were larger compared with any soft tissue liquefied with the same BH parameters, indicating higher susceptibility of hematomas to BH damage. These results suggest that clotted bovine blood with added thrombin is an acceptable in vitro model of both acute and chronic human hematomas for assessing the efficiency of BH liquefaction strategies.

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Audio Feedback for Improving the Accuracy of BWL Targeting

Record of Invention Number: 48254

Mike Bailey, Bryan Cunitz, Barbrina Dunmire, Christopher Hunter, Wayne Kreider, Adam Maxwell, Yak-Nam Wang


25 Jan 2018

Acoustics Air-Sea Interaction & Remote Sensing Center for Environmental & Information Systems Center for Industrial & Medical Ultrasound Electronic & Photonic Systems Ocean Engineering Ocean Physics Polar Science Center