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John A. Viator, Ph.D.
Department of Dermatology
Oregon Health & Science University
Photoacoustic imaging: The intersection of light and sound in biomedical diagnosis
Abstract
Biomedical photoacoustics, conceptually described as a laser induced
ultrasound, can be used to provide non-invasive diagnostic information about
biological tissue and its pathology. Photoacoustic waves are generated by
irradiating optical absorbers with fast laser pulses, giving rise to rapid
thermoelastic expansion manifested as acoustic waves. In biological tissue,
such as skin, the absorbers of interest are often melanin, hemoglobin, and
water, thus conditions related to melanin, blood, and tissue hydration can
be investigated. The combination of optical and acoustical interactions in
tissue allow high resolution imaging and robust signal propagation in
tissue, respectively.
The photoacoustic apparatus consists of a frequency doubled Nd:YAG laser
coupled to an optical parametric oscillator for tuning wavelengths
throughout much of the visible and near infrared spectrum, allowing
targeting of specific absorbers. Laser energy is either directed to tissue
either as a free beam or coupled into an optical fiber, which terminates in
a miniature probe with an acoustic sensor. The detected acoustic waves are
then analyzed for tissue mechanical and optical properties, and eventually
for depth profiling and imaging.
I will present a progression of work using photoacoustic methods, from depth
profiling of layered tissue phantoms, to in vivo diagnostic procedures
applied to dermal vascular lesions, burn depth, and imaging of melanin in
human skin. I will provide a framework from the theory of photoacoustic
generation and follow with depth profiling and imaging algorithms. The
theoretical limit of resolution for photoacoustic imaging (~1 –5 µm) will be
compared to the current practical limit (~25 –100 µm). I will also compare
the relative merits of photoacoustic imaging with established and emerging
imaging technologies, such as optical coherence tomography, magnetic
resonance imaging, and photothermal radiometry.
Biosketch
John A.Viator is a Senior Research Associate in the Department of
Dermatology at Oregon Health & Science University. His research focus is in
biomedical optics, particularly in photoacoustic imaging for diagnosing skin
pathology, including melanoma, vascular lesions, and burn injury. He also
holds appointments as Senior Scientist at Blue Road Research, Visiting
Researcher at Beckman Laser Institute at the University of California,
Irvine, and as a Project Officer for the Office of Naval Research. He
received a B.S. in physics from the University of Washington, an M.S. in
mathematics from the University of Oregon, and an M.S. in applied physics
and a Ph.D. in electrical engineering from Oregon Health & Science
University.
Wednesday, October 29, 2003
Bourns Hall, Room A265
10:10 a.m.-11:00 p.m.
(Refreshments will be served at 10:00 a.m.) |
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