Dr. James R. McLaughlan Profile

Dr. James R. McLaughlan

at Boston Univ

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Proceedings Article | 25 February 2010 Paper

Nanoparticle-targeted photoacoustic cavitation for tissue imaging

James McLaughlan, Ronald Roy, Hengyi Ju, Todd Murray

Proceedings Volume 7564, 756415 (2010) https://doi.org/10.1117/12.842415

KEYWORDS: Cavitation, Tissue optics, Nanoparticles, Optical spheres, Photoacoustic spectroscopy, Acoustics, Ultrasonography, Gold, Pulsed laser operation, Transducers

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Photoacoustic tomography is a non-invasive imaging technique based on the detection of broadband acoustic emissions generated by the absorption of light in tissue. This technique utilises the high contrast of optical imaging with high resolution from ultrasound imaging. However, the ability to detect these emissions above the noise level ultimately limits the depth to which imaging can be performed. Introduction of light-absorbing gold nanoparticles can improve the signal-to-noise ratio in tissue, through greater optical absorption and targeting specific cell populations, thereby enhancing contrast and the ability to delineate tissue types. For sufficiently high laser fluence incident on a nanoparticle, a transient vapour cavity is formed and undergoes inertial collapse, generating a broadband emission and possibly additional contrast. However, the laser fluence required to achieve this typically exceeds the maximum permissible exposure (MPE) for tissue. Through the combination of ultrasonic and optical pulses, the light and sound thresholds required to repeatedly generate inertial cavitation were reduced to 11.1 mJ/cm² and 1.5 MPa respectively. Experiments employed a transparent acrylamide gel possessing a small (<600 μm) spherical region doped with 80 nm diameter gold nanoparticles and simultaneously exposed to pulsed laser light (532 nm) and pulsed ultrasound (1.1 MHz). The amplitude of broadband emissions induced by both light and sound exceeded that produced by light alone by almost two orders of magnitude, thereby facilitating imaging a deeper depth within tissue. 2D images of doped regions generated from conventional photoacoustic and ultrasound-enhanced emissions are presented and compared.

Proceedings Article | 24 February 2010 Paper

Monitoring and guidance of high intensity focused ultrasound exposures in real time using acousto-optic imaging: feasibility and demonstration ex vivo

Puxiang Lai, James McLaughlan, Andrew Draudt, Todd Murray, Robin Cleveland, Ronald Roy

Proceedings Volume 7564, 75642B (2010) https://doi.org/10.1117/12.842358

KEYWORDS: Ultrasonography, Tissue optics, Acousto-optics, Tissues, Signal detection, Adaptive optics, Transducers, Imaging systems, Cavitation, Optical amplifiers

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High intensity focused ultrasound (HIFU) is a powerful noninvasive tool for targeted tissue ablation. Monitoring of the treatment process and efficacy in real time, however, remains challenging. The tissue necrosis during the HIFU exposure leads to changes in optical absorption and scattering coefficients. In this paper, we explore the use of acousto-optic imaging (AOI), a hybrid technique that combines ultrasound with diffuse light to obtain deep-tissue optical contrast at ultrasound resolution, to sense the changes in optical contrast at depth in tissue associated with the onset formation and development of the necrosed tissue region. In this technique, the tissue to be treated is illuminated with near-infrared light and a continuous, amplitude-modulated focused ultrasound beam is used to induce thermal tissue necrosis as well as the acousto-optic (AO) interaction. The AOI signal is detected via a photorefractive crystal (PRC)-based interferometer, and then fed into a lock-in amplifier tuned to the ultrasound modulation frequency. As a thermal lesion forms in the ultrasound focal zone, which is also the zone of AO interaction, the AOI signal diminishes in amplitude owing to enhanced optical attenuation. It is further shown that the reduction of the AOI signal is correlated with the volume of ensuing lesion. Therefore, the evolution of AOI signal as a function of time provides a means for continuous monitoring of HIFU treatment process as well as exposure guidance.

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