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Stuart Mitchell

Affiliate Senior Engineer






2000-present and while at APL-UW

Characterizing an agar/gelatin phantom for image guided dosing and feeback control of high-intensity focused ultrasound

Dunmire, B., J.C. Kucewicz, S.B. Mitchell, L.A. Crum, and K.M Sekins, "Characterizing an agar/gelatin phantom for image guided dosing and feeback control of high-intensity focused ultrasound," Ultrasound Med. Biol., 39, 300-311, 2013.

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1 Feb 2013

The temperature dependence of an agar/gelatin phantom was evaluated. The purpose was to predict the material property response to high-intensity focused ultrasound (HIFU) for developing ultrasound guided dosing and targeting feedback. Changes in attenuation, sound speed, shear modulus and thermal properties with temperature were examined from 20°C to 70°C for 3 weeks post-manufacture. The attenuation decreased with temperature by a power factor of 0.15. Thermal conductivity, diffusivity and specific heat all increased linearly with temperature for a total change of approximately 16%, 10% and 6%, respectively. Sound speed had a parabolic dependence on temperature similar to that of water. Initially, the shear modulus irreversibly declined with even a slight increase in temperature. Over time, the gel maintained its room temperature shear modulus with moderate heating. A stable phantom was achieved within 2 weeks post-manufacture that possessed quasi-reversible material properties up to nearly 55°C.

Novel high-intensity focused ultrasound clamp — potential adjunct for laparoscopic partial nephrectomy

Harper, J.D., A. Shah, S.B. Mitchell, Y.N. Wang, F. Starr, M.R. Bailey, and L.A. Crum, "Novel high-intensity focused ultrasound clamp — potential adjunct for laparoscopic partial nephrectomy," J. Endourol., 26, 1494-1499, doi:10.1098/end.2012.0107, 2012.

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1 Nov 2012

Partial nephrectomy (PN) can be technically challenging, especially if performed in a minimally invasive manner. Although ultrasound technology has been shown to have therapeutic capabilities, including tissue ablation and hemostasis, it has not gained clinical use in the PN setting. The purpose of this study is to evaluate the ability of a high-intensity ultrasound clamp to create an ablation plane in the kidney providing hemostasis that could potentially aid in laparoscopic PN.
A new instrument was created using a laparoscopic Padron endoscopic exposing retractor. Ultrasound elements were engineered on both sides of the retractor to administer high-intensity ultrasound energy between the two sides of the clamp. This high-intensity focused ultrasound (HIFU) clamp was placed 2 to 2.5 cm from the upper and lower poles of 10 porcine kidneys to evaluate its effectiveness at different levels and duration of energy delivery. PN transection was performed through the distal portion of the clamped margin. Kidneys postintervention and after PN were evaluated and blood loss estimated by weighing gauze placed at the defect. Histologic analysis was performed with hematoxylin and eosin and nicotinamide adenine dinucleotide staining to evaluate for tissue viability and thermal spread.
Gross parenchymal changes were seen with obvious demarcation between treated and untreated tissue. Increased ultrasound exposure time (10 vs 5 and 2 min), even at lower power settings, was more effective in causing destruction and necrosis of tissue. Transmural ablation was achieved in three of four renal units after 10 minutes of exposure with significantly less blood loss (<2 g vs 30-100 g). Nonviable tissue was confirmed histologically. There was minimal thermal spread outside the clamped margin (1.2-3.2 mm).
In this preliminary porcine evaluation, a novel HIFU clamp induced hemostasis and created an ablation plane in the kidney. This technology could serve as a useful adjunct to laparoscopic PN in the future and potentially obviate the need for renal hilar clamping.

Effect of low intensity pulsed ultrasound on mesenchymal stem cells

Ruan, J.L., Y.N. Wang, L.A. Crum, and S.B. Mitchell, "Effect of low intensity pulsed ultrasound on mesenchymal stem cells," J. Acoust. Soc. Am., 129, 2576, doi:10.1121/1.3588505, 2011.

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1 Apr 2011

Low intensity pulsed ultrasound (LIPUS) has been used to accelerate tissue regeneration; however, the biological mechanisms of LIPUS induced regeneration is not completely understood. The aim for this study is to elucidate the mechanical effect generated by US for the stimulation of mesenchymal stem cells (MSCs). MSCs were cultured on flexible cell culture membranes and stimulated by US for 10 min daily with acoustic intensities of 0, 6, 13.5, and 22.5 W/cm2. Cell proliferation and viability were evaluated by direct cell count and Alamar Blue assay. Morphological evaluation was performed and cell-matrix interactions were evaluated. Cell-matrix interaction was analyzed by immunochemical staining of focal adhesion proteins. LIPUS enhanced cell proliferation at higher intensities and there was an increase in cell viability after 4 consecutive days of US treatment. No morphological changes were observed in all treatments. Expression of focal adhesion protein, vinculin, was enhanced after 3 consecutive days of ultrasound treatment. Studies of media agitation did not show any enhancement effect in cell proliferation or focal adhesion protein expression. The results validates that US is able to influence the cell matrix interaction. Application of higher acoustic pressure on cell growth environment can stimulate MSC proliferation and focal adhesion.

More Publications


Method and apparatus for preparing organs and tissues for laparoscopic surgery

Patent Number: 9,198,635

Larry Crum, Mike Bailey, Peter Kaczkowski, Stuart Mitchell

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1 Dec 2015

High intensity ultrasound (HIU) is used to facilitate surgical procedures, such as a laparoscopic partial nephrectomy, with minimal bleeding. An apparatus is configured to emit HIU from one or more transducers that are attached to a minimally invasive surgical instrument. Such a tool preferably can provide sufficient clamping pressure to collapse blood vessels' walls, so that they will be sealed by the application of the HIU, and by the resulting thermal ablation and tissue cauterization. Such an instrument can provide feedback to the user that the lesion is completely transmural and that blood flow to the region distal of the line of thermal ablation has ceased. Similar instruments having opposed arms can be configured for use in conventional surgical applications as well. Instruments can be implemented with transducers on only one arm, and an ultrasound reflective material disposed on the other arm.

Method and Apparatus for Controlled Electrospinning

Patent Number: 9,085,830

Stuart Mitchell, Joan Sanders

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21 Jul 2015

An electrospinning apparatus and methodology is described that produces medical devices, such as scaffolds that induce the formation of a natural fibrous structure (primarily collagen and elastin) in a tissue-engineered medical device. The apparatus uses collection surfaces designed to manipulate or change the electrostatic field so that the electrospun fibers are arranged in desirable patterns that are similar to or mimic the fibrillar structure of an animal tissue. The manipulation results in fibers that are preferentially oriented in a predefined pattern. In addition, the interfiber space between the fibers and the fiber diameter are consistently within a predefined range. Using these techniques in conjunction with controlling polymer properties enables the production of a scaffold that has the structural and mechanical characteristics similar to the native tissue.

Methods and Apparatus for Blood Vessel Fusion

Record of Invention Number: 45347

Larry Crum, Stuart Mitchell, Robert Rho, Stephen Seslar


17 Aug 2010

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