Garrett Vermey, Dave Erdos

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Biomedical imaging modality based on the photoacoustic effect

Hybrid method which combines optics and ultrasound

Utilizes both photonic and mechanical energy, nonionizing ER and sound waves respectively

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Nonionizing waves used to excite and result in ultrasonic emission

Ultrasonic waves that are generated are used for image formation

2D or 3D images may be formed

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Rabbit’s Esophagus

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Photoacoustic effect first reported by Alexander Graham Bell in 1880

PA effect began to be used for the purposes of gas analysis in 1938

The development of the laser in 1960s 1970s – 1980s sensing applications began to

emerge 5

Mid 1990s brought the beginning of investigation for biomedical imaging

Early works progressed slowly till the early to mid 2000s

From that point on the field has witnessed major growth

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Conversion between light and acoustic waves from absorbance and localized thermal excitation

When rapid pulses of light are incident on matter they can be absorbed

The resulting energy will be radiated as heat The heat causes detectable sound waves due

to variations of pressure between mediums 7

Light can only penetrate soft tissue to a depth of ≈1mm before been scattered to much to create an image

But scattering doesn’t destroy the photons which can reach a depth of ≈7cm

Sound waves scatter ≈1000X less then light

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Molecules beneath the surface absorb light and create thermally induced pressure jumps that launch sound waves

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Major challenge of PAT Mostly has been used in other imaging

modalities (MRI, CT, etc.) Challenge is where the source of the wave

arises from Similar to identifying where thunder

originated in a storm Many different approaches have been taken

(Fourier domain analysis, analytic back-projection, Radon transforms etc.)

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Without signal processing reconstructed images could suffer from low resolution

Random noise removed by signal averaging

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Contrast agents are being used to increase sensitivity and specificity, nanoparticles and dyes

Can be administered through circulatory system or directly injected into the tissue of interest

Contrast agents that are with high absorption desired

Compared to dyes nanoparticle have a longer lifetime as well as high and tunable absorbance spectrum

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Used in detection of breast cancer

Superior to both common methods in used right now (x-ray mammography and ultrasound)

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Development of breast tissue commonly accompanied by angiogenesis

Blood is a good PA absorber, and PAT is a good detector of breast cancer

PAT is sensitive to tumor related vasculature, and has been proven through recent studies to detect tumors missed by x-ray mammography

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A) X-ray mammography B) Doppler Ultrasonography C) PAT

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Bones, particular large thick ones distort the acoustic signal

Scattering in the air cavities of the body

Need to be able to image deeper

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Photoacoustic imaging is starting to be used on human patients

First pre-clinical PAT systems now commercialized

Most immediate challenge is for clinical systems to make it through approval steps

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Lihong V. Wang. “Prospects of photoacoustic tomography”. (December 2008) http://www.ncbi.nlm.nih.gov/pmc/articles/pmc2647010/

Lihong V. Wang, Song Hu. “Photoacoustic Tomography: In Vivo Imaging from Organelles to Organs”. (March 2012) http://www.sciencemag.org/content/335/6075/1458.long

Benjamin Spike. “The Photoacoustic Effect”. (April 2006) http://uw.physics.wisc.edu/~timbie/P325/Spike_photoacoustic_effect.pdf

Wei Lu, Quian Huang, Geng Ku, Xiaoxia Wen, Min Zhou, Dimitry Guzatov, Peter Brecht, Richard Su, Alexander Oraevsky, Lihong V. Wang, Chun Li. “Photoacoustic imaging of living mouse brain vasculature using hollow gold nanospheres” (2009) http://www.sciencedirect.com/science/article/pii/S0142961209013660

Yao Sun, Huabei Jiang, Brian E. O’Neill. “Photoacoustic Imaging: An Emerging Optical Modality in Diagnostic and Theranostic Medicine”

http://www.omicsonline.org/2155-6210/2155-6210-2-108.php?aid=2275 Etienne De Montigny. “Photoacoustic Tomography :Principles and applications”. (2011)

http://www.polymtl.ca/phys/doc/art_4_3.pdf Mike Hatcher. “Photoacoustic imaging begins clinical move” (April 2012) http://optics.org/indepth/3/3/5 Changhui Li, Lihong V Wang. “Photoacoustic tomography and sensing in biomedicine” (August 2009)

http://iopscience.iop.org/0031-9155/54/19/R01/pdf/0031-9155_54_19_R01.pdf Jonathan Vizcarra. “New Imaging Technique Photoacoustic Tomography Ready For Clinical Use“ (March

2012) http://www.quantumday.com/2012/03/new-imaging-technique-photoacoustic.html Martin Rothlisberger “A Hot New Development: Photoacoustic Imaging” (November 2010)

http://www.chemistryviews.org/details/news/1388327/A_Hot_New_Development_Photoacoustic_Imaging.html

“Synchronized averaging” http://support.azimadli.com/vibman/synchronousaveraging.htm

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