Non-Contact Optical Ultrasound Concept for Biomedical Imaging

We examine the potential of a fully noncontact-standoff laser-ultrasound concept to generate and measure elastic waves in order to construct internal structure and matrix images within biological tissue. We use a pulsed optical laser (Q-switched) as an excitation source that converts optical energy...

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Bibliographic Details
Main Authors: Haupt,Robert W, Wynn,Charles M, Fincke,Jonathan, Zhang,Shawn, Anthony,Brian, Samir,Anthony
Format: Report
Language:English
Subjects:
Acoustics
diagnostic imaging
elastic waves
LDV(Laser Doppler Vibrometry)
medical elastography
Medical Facilities, Equipment and Supplies
photoacoustic tomography
tissues
ultrasounds
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Summary:We examine the potential of a fully noncontact-standoff laser-ultrasound concept to generate and measure elastic waves in order to construct internal structure and matrix images within biological tissue. We use a pulsed optical laser (Q-switched) as an excitation source that converts optical energy to ultrasonic waves within a tissue complex via photoacoustic (PA) mechanisms. Laser Doppler vibrometry (LDV) is then used to measure the returning signals on the tissue surface. We report that the photoacoustic generation of elastic waves from a short optical pulse produces the compilation of elastic body and surface waves including longitudinal, shear, Rayleigh, and Love wave components. Using information from the various wave types can yield 1) tissue and bone anatomical images for medical diagnosis and 2) mechanical property distributions that have important implications in the emerging field of medical elastography. We also examine the effects of optical excitation wavelength on the signal-to-noise ratio (SNR) and quality of ultrasonic images of the interior of tissue specimens. Optical wavelengths spanned the near infrared to the short wave infrared. In general, but with an important exception near 1550 nm, the known tissue absorptivity implies that longer wavelength light is more strongly absorbed than shorter wavelengths. The question is how this translates to propagating acoustic energy (ultrasonic waves) capable of penetrating into tissue in order to be useful for interior imaging. We observe that wavelengths near 1550nm produce acoustic energy with the highest SNR and thus the best quality interior images. A simple model based on the known tissue absorptivity and photoacoustic conversion is proposed to explain these results. Lastly, we present imaging capabilities using a non-contact laser ultrasound proof-of-concept system. SPI Journal of Biomedical Optics , 01 Jan 0001, 01 Jan 0001,