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Accueil du site > Séminaires, conférences > Séminaires du LIP > Séminaires en 2009 > Miniature dual-mode transducers for image-guided interstitial ultrasound therapy.

Miniature dual-mode transducers for image-guided interstitial ultrasound therapy.

Date : 30/01/2009 à 14h00

Intervenants :
- Neil OWEN, INSERM Unité 556 Therapeutic Applications of Ultrasound Lyon.

Résumé :

High-intensity ultrasound has been demonstrated as an effective modality for the treatment of many cancers. To date, a challenging aspect of this technology is the ability to monitor the formation of lesions in tissue and to identify the treatment endpoint at which a tumor and a safety margin are coagulatively necrosed. Within this context, dual-mode transducers have the potential to guide and monitor with ultrasound imaging the delivery of minimally-invasive interstitial ultrasound therapy. In this work, a miniature 5-element piezocomposite transducer was characterized in imaging and therapy modes, and then integrated with a probe for evaluation in vitro. The probe featured oscillatory motion to form sector images in several planes and to direct therapy. The cylindrically-focused transducer (f = 14 mm) had a rectangular aperture of 20 x 3.0 mm2 with 3.8 x 3.0 mm2 elements and 250 µm kerfs. 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 0.1 mm diameter wire though the focal plane, was 1.0 mm at -6 dB. During in vitro evaluation with porcine liver, an initial B-mode image was formed over a 140° sector. Then, high-intensity ultrasound was applied at several discrete angles to form a composite lesion. During therapy, pulse-echo data were collected periodically to monitor therapy with real-time M-mode imaging. After therapy, another B-mode image was formed, and lesion size was measured by gross histology. B-mode images adequately represented the liver structure within the 20 mm depth in which lesions were formed. Data from M-mode image analysis were consistent with lesion formation and suggested lesion depth. This work is part of an ongoing project to develop multi-element dual-mode transducers and therapeutic strategies for imaged-guided interstitial ultrasound therapy.