Neil Owen

French Institute of Health and Medical Research, Lutetia Parisorum, Île-de-France, France

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Publications (9)13.14 Total impact

  • [show abstract] [hide abstract]
    ABSTRACT: Interstitial ultrasound applicators can be a minimally invasive alternative for treating targets that are unresectable or are inaccessible by extracorporeal methods. Dual-mode transducers for ultrasound imaging and therapy were developed to address the constraints of a miniaturized applicator and real-time treatment monitoring. We propose an original treatment strategy that combines ultrasound imaging and therapy using a dual-mode transducer rotating at 8 revolutions per second. Real-time B-mode imaging was interrupted to emit high-intensity ultrasound over a selected therapy aperture. A full 360 degrees image was taken every 8th rotation to image the therapy aperture. Numerical simulations were performed to study the effect of rotation on tissue heating, and to study the effect of the treatment sequence on transducer temperature. With the time-averaged transducer surface intensity held at 12 W/cm(2) to maintain transducer temperature below 66 degrees C, higher field intensities and deeper lesions were produced by narrower therapy apertures. A prototype system was built and tested using in vitro samples of porcine liver. Lesions up to 8 mm were produced using a time-averaged transducer surface intensity of 12 W/cm(2) applied for a period of 240 s over a therapy aperture of 40 degrees. Apparent strain imaging of the therapy aperture improved the contrast between treated and spared tissues, which could not be differentiated on B-mode images. With appropriate limits on the transducer output, real-time imaging and deep thermal ablation are feasible and sustainable using a rotating dual-mode transducer.
    IEEE transactions on ultrasonics, ferroelectrics, and frequency control 05/2010; 57(5):1086-95. · 1.80 Impact Factor
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    ABSTRACT: Unresectable liver tumors are often treated with interstitial probes that modify tissue temperature, and efficacious treatment relies on image guidance for tissue targeting and assessment. Here, we report the in vivo evaluation of an interstitial applicator with a mechanically oscillating five-element dual-mode transducer. After thoroughly characterizing the transducer, tissue response to high-intensity ultrasound was numerically calculated to select parameters for experimentation in vivo . Using perfused porcine liver, B-mode sector images were formed before and after a 120-s therapy period, and M-mode imaging monitored the therapy axis during therapy. The time-averaged transducer surface intensity was 21 or 27 W/cm<sup>2</sup>. Electroacoustic conversion efficiency was maximally 72 ?? 3% and impulse response length was 295 ?? 1.0 ns at -6 dB. The depth of thermal damage measured by gross histology ranged from 10 to 25 mm for 13 insertion sites. For six sites, M-mode data exhibited a reduction in gray-scale intensity that was interpreted as the temporal variation of coagulation necrosis. Contrast ratio analysis indicated that the gray-scale intensity dropped by 7.8 ??3.3 dB, and estimated the final lesion depth to an accuracy of 2.3 ?? 2.4 mm. This paper verified that the applicator could induce coagulation necrosis in perfused liver and demonstrated the feasibility of real-time monitoring.
    IEEE Transactions on Biomedical Engineering 02/2010; · 2.35 Impact Factor
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    ABSTRACT: Medical imaging is a vital component of high intensity focused ultrasound (HIFU) therapy, which is gaining clinical acceptance for tissue ablation and cancer therapy. Imaging is necessary to plan and guide the application of therapeutic ultrasound, and to monitor the effects it induces in tissue. Because they can transmit high intensity continuous wave ultrasound for treatment and pulsed ultrasound for imaging, dual-mode transducers aim to improve the guidance and monitoring stages. Their primary advantage is implicit registration between the imaging and treatment axes, and so they can help ensure before treatment that the therapeutic beam is correctly aligned with the planned treatment volume. During treatment, imaging signals can be processed in real-time to assess acoustic properties of the tissue that are related to thermal ablation. Piezocomposite materials are favorable for dual-mode transducers because of their improved bandwidth, which in turn improves imaging performance while maintaining high efficiency for treatment. Here we present our experiences with three dual-mode transducers for interstitial applications. The first was an 11-MHz monoelement designed for use in the bile duct. It had a 25x7.5 mm(2) aperture that was cylindrically focused to 10mm. The applicator motion was step-wise rotational for imaging and therapy over a 360 degrees, or smaller, sector. The second transducer had 5-elements, each measuring 3.0x3.8 mm(2) for a total aperture of 3.0x20 mm(2). It operated at 5.6 MHz, was cylindrically focused to 14 mm, and was integrated with a servo-controlled oscillating probe designed for sector imaging and directive therapy in the liver. The last transducer was a 5-MHz, 64-element linear array designed for beam-formed imaging and therapy. The aperture was 3.0x18 mm(2) with a pitch of 0.280 mm. Characterization results included conversion efficiencies above 50%, pulse-echo bandwidths above 50%, surface intensities up to 30 W/cm(2), and axial imaging resolutions to 0.2 mm. The second transducer was evaluated in vivo using porcine liver, where coagulation necrosis was induced up to a depth of 20 mm in 120 s. B-mode and M-mode images displayed a hypoechoic region that agreed well with lesion depth observed by gross histology. These feasibility studies demonstrate that the dual-mode transducers had imaging performance that was sufficient to aid the guidance and monitoring of treatment, and could sustain high intensities to induce coagulation necrosis in vivo.
    Ultrasonics 08/2009; 50(2):216-20. · 2.03 Impact Factor
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    ABSTRACT: Interstitial probes with dual‐mode transducers are effective devices to guide and monitor with ultrasound imaging the application of ultrasound therapy. Here, a dual‐mode 5‐element transducer, with oscillatory motion for sector imaging and directive therapy, was characterized and evaluated in vitro with porcine liver. The transducer had 3.8×3.0‐mm2 elements, a 20×3.0‐mm2 aperture, and was cylindrically focused to 14‐mm. In therapy mode, elements were maximally efficient, 72±4% (ave±std), at 5.6‐MHz. In imaging mode, the pulse‐echo impulse response for each electrically‐matched element was 160±16 ns long at −6 dB, and insertion loss was minimally 9.8±0.5 dB at 5.2‐MHz. Electrical crosstalk was less than −57 dB at 5.6‐MHz. Lateral resolution, measured by scanning a wire of 0.1‐mm diameter wire though the focal plane, was 1.0‐mm at −6 dB. During experiment, an initial B‐mode image was formed over a 140° sector. Then, therapy was applied for 90 s, with 18‐W/cm2 transducer surface intensity, at each of 5 angles (Δθ = 20°) to form volumes of composite protein denaturization. Pulse‐echo data were collected periodically to monitor therapy with real‐time M‐mode imaging. After therapy, another B‐mode image was formed, and the depth of protein denaturization was measured by gross histology. B‐mode images adequately represented the liver structure. Analysis of M‐mode images was consistent with gross histology.
    AIP Conference Proceedings. 04/2009; 1113(1):347-351.
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    ABSTRACT: Miniature flat ultrasound transducers have shown to be effective for a large variety of thermal therapies, but the associated superficial heating implicates developing original strategies in order to extend therapeutic depth. The goal of the present paper is to use ultrasound contrast agents (UCA) to increase remote attenuation and heating. Theoretical simulations demonstrated that increasing attenuation from 0.27 to 0.8 Np/cm at 10 MHz beyond a distance of 18 mm from the transducer should result in longer thermal damages due to protein coagulation in a tissue mimicking phantom. Contrast agents (BR14, Bracco, Plan-les-Ouates, Switzerland) were embedded in thermo-sensitive gel and attenuations ranging from 0.27 to 1.33 Np/cm were measured at 10 MHz for concentrations of BR14 between 0 and 4.8%. Thermal damages were then induced in several gels, which had different layering configurations. Thermal damages, 12.8mm in length, were obtained in homogeneous gels. When mixing contrast agents at a concentration of 3.2% beyond a first 18 mm-thick layer of homogeneous gel, the thermal damages reached 21.5mm in length. This work demonstrated that contrast agents can be used for increasing attenuation remotely and extending therapeutic depth induced by a non-focused transducer. Additional work must be done in vivo in order to verify the remote-only distribution of bubbles and associated increase in attenuation.
    Ultrasonics 09/2008; 49(2):172-8. · 2.03 Impact Factor
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    ABSTRACT: We present a summary of Inserm's experience with high power sources, which are necessary for ultrasound thermal therapy and lithotripsy. Moreover, generating high intensity pseudo-continuous waveforms or high pressure pulses imposes different constraints on the transducer materials, specifically heat and mechanical stress. For thermal therapy, miniature piezoceramic transducers were used for interstitial, intratumoral, and endoluminal applicators. These probes operated at surface intensities up to 50 Wcm(2) and generated elementary lesions in vivo within tens of seconds. Piezocomposite transducers were developed for large-aperture, highly-focused beams used in extracorporeal or intraoperative treatments. Focal intensities were 1000 Wcm(2) or higher and up to 256 elements were utilized. Miniaturized piezocomposite transducers are currently being developed for dual-mode imaging and therapy. For lithotripsy, piezoelectric shock wave generators were developed as alternatives to electrohydraulic or electromagnetic generators. Using piezocomposite materials and a novel prestraining method increased transducer surface pressure compared to a multielement piezoceramic design, and therefore halved the aperture diameter. In in vitro tests, plaster kidney stone models were comminuted with approximately 200 shock waves, a number comparable to values published for electrohydraulic generators, the current "gold" standard. This work contributes to the advancement of transducer performance in therapeutic ultrasound. [Supported by Inserm Post-doctoral Fellowship.].
    The Journal of the Acoustical Society of America 06/2008; 123(5):3782. · 1.65 Impact Factor
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    ABSTRACT: Miniature dual-mode transducers can be used for minimally invasive treatment of deep-seated tumors. While in contact with the tissue, the transducer guides and monitors localized necrosis. Here, an oscillating 5-element piezo-composite transducer was characterized, and then evaluated in vitro using porcine liver. Each element was 3.0 x 3.8 mm(2) with a geometric cylindrical focus of 14 mm. The transmit frequency was determined by the maximal electro-acoustic efficiency, 65%, which was found at 5.6 MHz. The transmit-receive impulse response was 400 ns long at -6 dB, and the -6 dB fractional bandwidth, centered at 5.6 MHz, was 30%. Axial and lateral resolution measured with a 0.1 mm diameter wire was 0.5 mm and 2.0 mm, respectively. For therapy, all elements radiated simultaneously, and for imaging, independently. Treatment was performed at increments of 20 degrees to form a composite volume of necrosis. At each angle, ultrasound was applied for 60 s at a transducer surface intensity of 15 Wcm(2). Pulse-echo data were recorded while the transducer oscillated over a 180 degrees sector to form images before and after treatment at each angle. Gross examination of lesion size agreed well with echogenic region size in the images. [Supported by ANR and Inserm Post-doctoral Fellowship.].
    The Journal of the Acoustical Society of America 06/2008; 123(5):2997. · 1.65 Impact Factor
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    ABSTRACT: Aggressive treatment of localized hepatic metastases, by surgery or other means, was proven to be a viable strategy for improving the prognoses of many patients. In that context, thermal ablation by high intensity ultrasound was proposed and used in clinics. However, for treating deep-seated tumors and in most cases, radiofrequency and cryotherapy probes are applied interstitially. Interstitial ultrasound applicators were proposed as an intermediate solution. The treatment can be focused, deeper than with other physical agents, and the transducer can eventually both treat and image tissues. In our experience, two approaches were investigated: percutaneous and intratissular, or endo vascular. The active element was a miniature flat transducer operating at a frequency of 5 MHz, for a satisfactory tradeoff between beam penetration and energy absorption. In vivo trials on a porcine model demonstrated that both procedures are minimally invasive and that large thermal lesions, up to 20 mm deep, can be obtained. Technological improvements such as the use of dual mode transducers (for imaging and therapy) or the performance under MRI guidance allowed monitoring the treatment in real-time.
    The Journal of the Acoustical Society of America 06/2008; 123(5):2996. · 1.65 Impact Factor
  • [show abstract] [hide abstract]
    ABSTRACT: Interstitial probes have been shown as effective devices to deliver high-intensity ultrasound therapy. Here, cylindrically-focused dual-mode transducers with either one or 5-elements were characterized, and a monoelement probe was evaluated in vitro. In therapy mode, the transducers were maximally efficient (> or =70%) at 5.6 MHz with surface intensities up to 20 W/cm(2). In imaging mode, fractional bandwidths were 46% and 50+/-4% (ave+/-std) for the monoelement and 5-element transducers respectively. Axial and lateral resolutions were 0.5 mm and 1.0 mm, respectively, for both transducers as measured with a point scatterer in the focal plane. After characterization, the oscillating probe was used to image and apply therapy to porcine liver. B-mode images over a 140 degrees sector were formed before and after therapy, which was applied for 90 s at each of 5 angles separated by 20 degrees (e.g. -40 degrees , -20 degrees, 0 degrees, 20 degrees, 40 degrees) to form a composite lesion. Transducer surface intensity was 18 W/cm(2). Therapy was interrupted at 125 ms intervals to collect pulse/echo data along the therapy axes. Data were displayed in real-time as an M-mode image to monitor therapy. B-mode images adequately represented the liver tissue. M-mode image data agreed well with the formation of lesions in the liver.
    Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 01/2008; 2008:3669-72.

Publication Stats

21 Citations
13.14 Total Impact Points

Institutions

  • 2010
    • French Institute of Health and Medical Research
      Lutetia Parisorum, Île-de-France, France
  • 2009
    • University of Lyon
      Lyons, Rhône-Alpes, France
    • University of Washington Seattle
      Seattle, Washington, United States
  • 2008
    • Unité Inserm U1077
      Caen, Lower Normandy, France