A PVDF receiver for ultrasound monitoring of transcranial focused ultrasound therapy.

Department of Imaging Research, Sunnybrook Health Sciences Centre, Toronto, ON M4N3M5, Canada.
IEEE transactions on bio-medical engineering (Impact Factor: 2.23). 09/2010; 57(9):2286-94. DOI: 10.1109/TBME.2010.2050483
Source: PubMed

ABSTRACT Focused ultrasound (FUS) shows great promise for use in the area of transcranial therapy. Currently dependent on MRI for monitoring, transcranial FUS would benefit from a real-time technique to monitor acoustic emissions during therapy. A polyvinylidene fluoride receiver with an active area of 17.8 mm (2) and a film thickness of 110 mum was constructed. A compact preamplifier was designed to fit within the receiver to improve the receiver SNR and allow the long transmission line needed to remove the receiver electronics outside of the MRI room. The receiver was compared with a 0.5 mm commercial needle hydrophone and focused and unfocused piezoceramics. The receiver was found to have a higher sensitivity than the needle hydrophone, a more wideband response than the piezoceramic, and sufficient threshold for detection of microbubble emissions. Sonication of microbubbles directly and through a fragment of human skull demonstrated the ability of the receiver to detect harmonic bubble emissions, and showed potential for use in a larger scale array. Monitoring of disruption of the blood-brain barrier in rats showed functionality in vivo and the ability to detect subharmonic, harmonic, and wideband emissions during therapy. The receiver shows potential for monitoring acoustic emissions during treatments and providing additional parameters to assist treatment planning. Future work will focus on developing a multi-element array for transcranial treatment monitoring.

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    • "However, the nonlinear nature of bubble oscillations allows using the subharmonic to detect stable cavitation experimentally (Neppiras 1968, Mestas et al 2003, Vykhodtseva et al 1995, McLaughlan et al 2010). Subharmonic emissions from cavitation are well established theoretically (Eller and Flynn 1969, Prosperetti 1974, Katiyar and Sarkar 2011), and are known to correlate experimentally with several in vivo and in vitro bioeffects, such as ultrasound-enhanced thrombolysis (Prokop et al 2007), disruption of the blood brain barrier (O'Reilly and Hynynen 2010), chemotherapy drug release from micelles (Husseini et al 2005), and enhanced heating in focused ultrasound surgery (Sokka et al 2003). Thus knowledge of the threshold of subharmonic emissions could be used to gauge the potential for clinically beneficial bioeffects. "
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    ABSTRACT: The mechanical index (MI) was formulated to gauge the likelihood of adverse bioeffects from inertial cavitation. However, the MI formulation did not consider bubble activity from stable cavitation. This type of bubble activity can be readily nucleated from ultrasound contrast agents (UCAs) and has the potential to promote beneficial bioeffects. Here, the presence of stable cavitation is determined numerically by tracking the onset of subharmonic oscillations within a population of bubbles for frequencies up to 7 MHz and peak rarefactional pressures up to 3 MPa. In addition, the acoustic pressure rupture threshold of an UCA population was determined using the Marmottant model. The threshold for subharmonic emissions of optimally sized bubbles was found to be lower than the inertial cavitation threshold for all frequencies studied. The rupture thresholds of optimally sized UCAs were found to be lower than the threshold for subharmonic emissions for either single cycle or steady state acoustic excitations. Because the thresholds of both subharmonic emissions and UCA rupture are linearly dependent on frequency, an index of the form I(CAV) = P(r)/f (where P(r) is the peak rarefactional pressure in MPa and f is the frequency in MHz) was derived to gauge the likelihood of subharmonic emissions due to stable cavitation activity nucleated from UCAs.
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    ABSTRACT: A 32 element receiver array was designed and integrated into an existing 1372 element transcranial therapy array to introduce real-time treatment monitoring capabilities. A semi-randomized array layout allowed signals from a narrowband source to be detected and localized within the array field of view. The combined array was used to sonicate microbubbles and detect their emissions both directly and through a human skull cap. Harmonic emissions were detected at realistic treatment pressures, and passive beamforming was used to localize the microbubble transcranially. Future work focus on further characterizing the combined device. Keywords-Blood-brain barrier (BBB), focused ultrasound (FUS), polyvinylidene fluoride (PVDF) hydrophone, transcranial therapy
    01/2010; DOI:10.1109/ULTSYM.2010.5935751
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