Schlieren observation of therapeutic field in water surrounded by cranium radiated from 500 kHz ultrasonic sector transducer

Azuma, Takashi; Kawabata, K.; Umemura, Shin‐ichiro; Ogihara, Makoto; Kubota, Jun; Sasaki, Akira; Furuhata, Hiroshi

doi:10.1109/ultsym.2004.1417934

Cited by 14 publications

(9 citation statements)

References 8 publications

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“…However, low frequencies can also give rise to standing waves in the brain, since the attenuation in brain tissue is lower and reflections at the brain/skull interface are high. Azuma et al [2005] observed standing wave formation inside the skull at an insonation frequency of 500 kHz using Schlieren imaging, while at 2 MHz no standing waves were detected.…”

Section: Introductionmentioning

confidence: 93%

The impact of standing wave effects on transcranial focused ultrasound disruption of the blood–brain barrier in a rat model

2010

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Microbubble mediated disruption of the blood brain barrier (BBB) for targeted drug delivery using focused ultrasound shows great potential as a therapy for a wide range of brain disorders. This technique is currently at the pre-clinical stage and important work is being conducted in animal models. Measurements of standing waves in ex vivo rat skulls were conducted using an optical hydrophone and a geometry dependence was identified. Standing waves could not be eliminated through the use of swept frequencies, which have been suggested to eliminate standing waves. Definitive standing wave patterns were detected in over 25% of animals used in a single study. Standing waves were successfully eliminated using a wideband composite sharply focused transducer and a reduced duty cycle. The modified pulse parameters were used in vivo to disrupt the BBB in a rat indicating that, unlike some other bioeffects, BBB disruption is not dependant on standing wave conditions. Due to the high variability of standing waves and the inability to correctly estimate in situ pressures given standing wave conditions, attempts to minimize standing waves should be made in all future work in this field to ensure that results are clinically translatable.

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Section: Introductionmentioning

confidence: 93%

The impact of standing wave effects on transcranial focused ultrasound disruption of the blood–brain barrier in a rat model

2010

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“…The sound pressure distribution of ultrasonic waves was measured optically using Schlieren imaging technology (18)(19)(20). The Schlieren imaging system was built in-house and consisted of a point light source (wavelength ¼ 532 nm, 100 mW), a spatial filter (pinhole size ¼ 10 mm), a water tank for submersion of the ultrasound probe, two lenses (diameter ¼ 75 mm, focal length ¼ 150 mm), and a charge-coupled device camera (QImaging, Pleasanton, CA).…”

Section: Schlieren Visualization Of Ultrasound Wave Fieldsmentioning

confidence: 99%

In vivo MR quantification of superparamagnetic iron oxide nanoparticle leakage during low‐frequency‐ultrasound‐induced blood–brain barrier opening in swine

Liu

Chen

Yang

et al. 2011

Magnetic Resonance Imaging

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Purpose: To verify that low-frequency planar ultrasound can be used to disrupt the BBB in large animals, and the usefulness of MRI to quantitatively monitor the delivery of superparamagnetic iron oxide (SPIO) nanoparticles into the disrupted regions.Materials and Methods: Two groups of swine subjected to craniotomy were sonicated with burst lengths of 30 or 100 ms, and one group of experiment was also performed to confirm the ability of 28-kHz sonication to open the BBB transcranially. SPIO nanoparticles were administered to the animals after BBB disruption. Procedures were monitored by MRI; SPIO concentrations were estimated by relaxivity mapping.Results: Sonication for 30 ms created shallow disruptions near the probe tip; 100-ms sonications after craniotomy can create larger and more penetrating openings, increasing SPIO leakage $3.6-fold than 30-ms sonications. However, this was accompanied by off-target effects possibly caused by ultrasonic wave reflection. SPIO concentrations estimated from transverse relaxation rate maps correlated well with direct measurements of SPIO concentration by optical emission spectrometry. We have also shown that transcranial low-frequency 28-kHz sonication can induce secure BBB opening from longitudinal MR image follow up to 7 days. Conclusion:This study provides valuable information regarding the use low-frequency ultrasound for BBB disruption and suggest that SPIO nanoparticles has the potential to serve as a thernostic agent in MRI-guided ultrasound-enhanced brain drug delivery.

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“…Low-frequency ultrasound sonication provides the advantage of good skull penetration, but a standing wave can be produced in brain [7]. Such a standing wave forms during lower frequency sonication due to diffraction and scattering of the traveling ultrasonic wave and the reflection of energy at the interface between heterogeneous tissue (especially at the brain tissue-skull interface), which leads to the reflected wave interfering with the traveling wave and thereby forming stationary acoustic pressure nodes (positive peak) and antinodes (negative peak).…”

Section: Resultsmentioning

confidence: 99%

A prototype design of a low-frequency hemispherical ultrasound phased-array system for transcranial blood-brain barrier (BBB) disruption

Liu

Chen

Kuo

et al. 2008

2008 IEEE Ultrasonics Symposium

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The purpose of this study was to demonstrate a prototype design of a low-frequency multiple-channel hemispherical focused-ultrasound phased-array system for transcranial disruption of the blood-brain barrier (BBB). In this study, we have presented a prototype design of a multiplechannel ultrasound hemispherical phased-array system to perform localized BBB disruption. To our knowledge this is the first phased-array system employing ultrasound at a frequency range suitable for transcranial sonication for BBB disruption. In our system design, the driving system includes a microcontroller/ field-programmable-gate-array (FPGA)-based control kernel with multiple-channel driving circuits implemented by a highvoltage switching/ LC-resonance/ impedance-matching circuit module. Three hemispherical phased arrays comprising 22, 31, 48, and 80 elements were fabricated and tested. The pressure distributions at the geometric center and at off-center positions were tested experimentally. The focal performance of the different hemispherical arrays was also evaluated theoretically. A 32-channel ultrasound driving system tunable in the frequency range from 200 to 400 kHz was designed for producing a suitable ultrasound output for BBB disruption. Results showed that the developed phased-array system can successfully drive the hemispherical array with multiple-channel ultrasound signals with independent phase control at 8-bit resolution. Preliminary animal experiments confirm its feasibility of disrupting the BBB through the intact animal skull. The described system could act as a platform design example or a reference for the development of a transcranial focused-ultrasound phased-array system for the clinical application of brain drug delivery.

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Schlieren observation of therapeutic field in water surrounded by cranium radiated from 500 kHz ultrasonic sector transducer

Cited by 14 publications

References 8 publications

The impact of standing wave effects on transcranial focused ultrasound disruption of the blood–brain barrier in a rat model

The impact of standing wave effects on transcranial focused ultrasound disruption of the blood–brain barrier in a rat model

In vivo MR quantification of superparamagnetic iron oxide nanoparticle leakage during low‐frequency‐ultrasound‐induced blood–brain barrier opening in swine

A prototype design of a low-frequency hemispherical ultrasound phased-array system for transcranial blood-brain barrier (BBB) disruption

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