Gruneisen coefficient optical absorption coefficient

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Unformatted text preview: P- selectin …looking for inflammatory markers, selective to inflammation around endothelium of colon o Can target for angiogenesis, cell adhesion (I- CAM, P- CAM) Ultrasound vs Photo o Ultrasound – standing at edge of canyon, shout, get sound back o Photoacoustic – like lightning and thunder §༊ zap with short laser pulse (quick), listen for sound coming back (slow) How it works o Photoabsorber = tissue, nanoparticle o Pulse tissue with nanosecond laser à༎ photoabsorber converts light to heat, undergoes rapid thermoelastic expanision à༎ emits wave…see slide Confinement o Need relaxation which results in the signal o Need to stop pulsing the laser, before heat diffused away • • • • • • • o o o Signal o o Shorter time period so tissue expands and contracts (listen) Stress confinement = shorter time scale than Thermal confinement Use 5 nanosecond pulse duration in his lab P0 – initial pressure at absorber Depends on 3 main factors..Gruneisen coefficient, optical absorption coefficient (how efficiently photoabsorber turns light into heat) Coefficient o Beta = how easily tissue can expand o Cp = how easily heat can be retained in a medium o Vs = how easily sound can travel though medium (close to water) Fluence o Problem with photo acoustic imaging = getting light to region of interest (dimmer as deeper)…due to absorption and scattering…restricts us to 5 cm o Need to know much light reached area to §༊ Monte Carlo simulation – simulate one photo…send another, simulate that §༊ Diffusion approx....
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This note was uploaded on 05/15/2012 for the course BME 251 taught by Professor Staff during the Spring '08 term at University of Texas at Austin.

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