Other Laser Surgery Laser Tonsillectomy Use CO 2 with mirror bouncing system Operation takes 15 minutes, no pain Cauterizes blood vessels & Lymphatic

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Cody Tucker
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1 Other Laser Surgery Laser Tonsillectomy Use CO 2 with mirror bouncing system Operation takes 15 minutes, no pain Cauterizes blood vessels & Lymphatic vessels no blood in throat Patient eat & drink just after operation unlike regular surgery

Gastrointesinal Surgery Uses fiber to bring in Argon Beam Same system my combine CO 2 gas to remove blood Cauterizes blood vessels Beam used to stop bleeding internally Esophagus, Stomach &

2 Gastrointesinal Surgery Uses fiber to bring in Argon Beam Same system my combine CO 2 gas to remove blood Cauterizes blood vessels Beam used to stop bleeding internally Esophagus, Stomach & Intestines Endoscopic (Fiber Optic) Laser Fallopian Tube Surgery Blockages in Fallopian tubes common cause of infertility in Women Use Endoscopic Laser fiber optic direction of CO 2 beam Burns away blockages, in 1-2 pulses Throat through Endoscope

3 Laser Dermatology (Skin Operations) Use the ability of the Laser to penetrate the skin Most common Argon laser removing skin discolourations eg Portwine marks: blood coloured birth defects Argon laser bleaches out blood spots Green light strongly absorbed by the red blood colour defects Much less absorbed by skin Almost removes such spots as they are near the surface

4 Laser Tatoo Removal Laser tattoo removals: done with Nd:Yag Nd:Yag Near IR light penetrates skin to tattoo depth Near IR strongly absorbed by dye: bleaches tattoo dye, but is weakly absorbed by skin so no damage to skin

Photoradiation Therapy Herpes Uses laser light to cause direct or indirect treatment eg Herpes virus creates lesions in skin and moist tissue Little in conventional treatment CO 2 used to destroy

5 Photoradiation Therapy Herpes Uses laser light to cause direct or indirect treatment eg Herpes virus creates lesions in skin and moist tissue Little in conventional treatment CO 2 used to destroy diseased cells & virus Beam directed on lesions using a microscope destroys tissue without bleeding Cancer PhotoDynamic Therapy (PDT) Patient injected with dye (eg HpD) Dye absorbed preferentially by Cancer tissue normal tissue excretes dye Exposed to 630 nm HpD has photochemical reaction produces a poison directly only in cancer tissue 630 nm obtained from Argon pumped Dye laser Laser Acupuncture He-Ne laser, penetrates 3-10 mm Laser irradiated for 60 sec at 2 mw controversial process

6 Ophthalmology (eye operations) & Dentistry Most common attaching detached retinas Uses Argon laser beam (Sometimes Ruby laser) Beam strongly absorbed by blood Creates a burn scar which reattaches retina Laser cornea shaping with Eximers (already discussed) Eximer also for Dentistry removal of diseased soft tissue

Optical Scattering in Tissue Within a medium light can be absorbed or scattered Ideally scattering does not absorb light but only changes direction But may remove energy from light (change

7 Optical Scattering in Tissue Within a medium light can be absorbed or scattered Ideally scattering does not absorb light but only changes direction But may remove energy from light (change wavelength) Generally occurs with non-homogeneous mediums Highly material specific Dominant effect in air. fog and turbid media e.g. tissue As object moves into fog it becomes blurred Reason scatted light contains little information about object Scattered light hides the object with distance E.g. objects in fog disappear when scattering gets high enough Effects Non-deterministic wave propagation Focusing of light not really possible Bolus or large ball of light created

Diffusion of Photons in Scattering Media Light entering Tissue breaks into different types 1 Photons may be absorbed 2 Photons may be highly scattered (many paths) until nearly uniform Scattered

8 Diffusion of Photons in Scattering Media Light entering Tissue breaks into different types 1 Photons may be absorbed 2 Photons may be highly scattered (many paths) until nearly uniform Scattered photons lose almost all information of internal structure 3 Photons may travel without scattering: called Ballistic photon If photon scattered: but nearly ballistic path called quasi-ballistic 4 Photons may be reflected back from the medium

9 Scattering With Depth When light in absorbing medium follows Beer Lambert Law With μ a = absorption coefficient (cm -1 ) I( z ) = I 0 exp( μa z ) Scattering also follows Beer s Law but with scattering portion Now add scattering coefficient μ s (cm -1 ) Combined effect of absorption+ scattering is ( z) I exp( [ μ + μ ] z) I = 0 a s Here we measure not how much light leaves material, But rather how much light continuous along original path Called Ballistic Photons In tissue, μ a and μ s are very different Both are wavelength dependent Both exhibit molecular specificity Typical values in breast μ a =0.2cm -1, μ s =400cm μ a =0.2cm -1, μ s =50cm -1 Also use Mean Free Path (MFP) = 1/μ

Anisotropy and Reduced Scatter Factor Light in tissue does not scatter evenly Anisotropy is to alter scattering In tissue light tends to be more forward scattered This is measured by an anisotropy

10 Anisotropy and Reduced Scatter Factor Light in tissue does not scatter evenly Anisotropy is to alter scattering In tissue light tends to be more forward scattered This is measured by an anisotropy factor g g is average scattered photons into cos(θ) over all directions g = 0 means isotropic scattering g = 1 is total forward scattering g = -1 total reverse scattering (ie reflection) In most materials 0 < g <1 Get an effective scattering coefficient μ eff (or μ ) where μ eff = μ 1 s ( g) μ eff adds up the effect of a random walk of scatters With g=0.9, then μ eff = μ s /10 Note if g = 1 (full forward scattering) μ eff = 0 Reason: fully forward scattering photon continues in original path Scattering has nill effect

Optical Tomography in Tissue Aim image through tissue like an X-ray Reason is that X-rays damage tissue Also different tissue affects different wavelengths X-ray is only affected by tissue density,

11 Optical Tomography in Tissue Aim image through tissue like an X-ray Reason is that X-rays damage tissue Also different tissue affects different wavelengths X-ray is only affected by tissue density, not type Hence can tell state of the tissue by looking at different λ Example blood changes colour & absorption with oxyget Oxygenated red, deoxygenated blue By look at 650 nm see large difference While at 800 nm both are same Simple diode sensor used for this

Optical Tomography Three OT methods: Time of flight (Time Domain) Phase Coherence Domain Angular Domain Imaging Time Domain Based on path length Shortest path photons arrive first Launch very

12 Optical Tomography Three OT methods: Time of flight (Time Domain) Phase Coherence Domain Angular Domain Imaging Time Domain Based on path length Shortest path photons arrive first Launch very short pulse Few Femtosec Ballistic arrive first Quasi ballistic next Scattered last Use high speed shutter to select Problem: high speed laser expensive Also FDA worried about impact of short pulses

Optical Coherence Tomography Longer path means that phase shift in coherent

tissue, other to reference Michelson interferometer methods By adjusting

unscattered Can see with high depth & size defination (few microns) But

13 Optical Coherence Tomography Longer path means that phase shift in coherent light Consider starting with a coherent source (laser) 2 paths: one to tissue, other to reference Michelson interferometer methods By adjusting reference delay scan return in phase Hence can separate scattered from unscattered Can see with high depth & size defination (few microns) But only with limited depth (few mm) in scattering Best place eyes (only limited scattering)

14 Angular Domain Imaging OT Laser source aligned to small acceptance angle angular filters Ballistic/quasi-ballistic light deviates only small angles Most scattered light outside acceptance angle

ADI Imaging Use a micromachined collimator for the

Tunnels spaced on 102 µm centers Aspect ratio ~200:1

29º aspect ratio micromachined tunnels Use test phantoms

50 µm) Scan the image Can detect at 9x10 9 scattering

15 ADI Imaging Use a micromachined collimator for the angular filters Use high 51 µm diameter x 1 cm length Tunnels spaced on 102 µm centers Aspect ratio ~200:1 Acceptance angle ~0.29º aspect ratio micromachined tunnels Use test phantoms in 5 cm scattering fluid Use lines/spaces (200, 150, 100, 50 µm) Scan the image Can detect at 9x10 9 scattering ratio Trade off object size ( μm) versus depth (cm s) Scattered only light ADI imaging of um lines

Optical Wave Guides & Fiber Optics

Optical Wave Guides & Fiber Optics Optical wave guides are the basis of optical communications Wave guides consist of a high index inner core/layer n 1 Surrounded by a lower index cladding n 2 This creates