1. Center for Biomedical Optics and New Laser Systems L.R.Lindvold - 20/05/2015 BIOMEDICAL APPLICATIONS OF LASERS; A REVIEW LARS LINDVOLD OVC ApS CAT SCIENCE PARK

2. Center for Biomedical Optics and New Laser Systems L.R.Lindvold - 20/05/2015 FUNDAMENTAL PROPETIES OF LASER LIGHT ! Spatial coherence; facilitates focusing to small spot size 1-10 micron ! Temporal coherence; monochromatic light selective absorption in chromophores ! Fast pluses 10 -15 - 10 -6 sec  time resolved spectroscopy and two-foton reactions and laser inducered plasma

3. Center for Biomedical Optics and New Laser Systems L.R.Lindvold - 20/05/2015 INTERACTIONS BETWEEN LIGHT AND TISSUE Possible effects: ! Photochemical ! Thermal ! Photoinduced plasma ! Photoablation

4. Center for Biomedical Optics and New Laser Systems L.R.Lindvold - 20/05/2015 ABSORPTIONS PROPERTIES OF TISSUE COMPONENTS

5. Center for Biomedical Optics and New Laser Systems L.R.Lindvold - 20/05/2015 PHOTOCHEMICAL EFFECTS PHOTODYNAMIC THERAPY (PDT) ! Selective absorption of dyes in carcionoma. Irradiation with laser light (600-800 nm) forms free radicals that acts as cell poison. ! Antibody/antigen coupled to photosensitiser ! Useful in diagnostics (fluorescence by excitation 400-500 nm)

6. Center for Biomedical Optics and New Laser Systems L.R.Lindvold - 20/05/2015 EXAMPLE OF PDT The bladder seen through an endoscope in white light The bladder seen through endoscope with blue laser light after ALA5 treatment. Red fluorescence indicates tumor

7. Center for Biomedical Optics and New Laser Systems L.R.Lindvold - 20/05/2015 TWO-PHOTON PDT The advent of femto second lasers has open up the avenue of exciting dyes by two photon absorption. Using this modality offers a very high degree of spatial confinement. 1-photon2-photon

8. Center for Biomedical Optics and New Laser Systems L.R.Lindvold - 20/05/2015 COAGULATION (60-100 O C) Proteins denaturates and DNA/RNA melts. Suitable for closing small blood vessels. ! Haemorrhaging on the retina ! Portvine stains ! Haemangioma ! Bleeding ulcers in the stomach ! Glueing together tissue (optical suture)

9. Center for Biomedical Optics and New Laser Systems L.R.Lindvold - 20/05/2015 PHOTOCOAGULATION (1) Haemorrhaging on the retina Fundus image of Retina after laser treatment Laser ofthalmoscope for photocoagulation

10. Center for Biomedical Optics and New Laser Systems L.R.Lindvold - 20/05/2015 PHOTO COAGULATION (2) Typical applications in dermatology include haemangiomas and Portwine stains. Blood vessels are closed with either Ar-ion (515 nm) or Nd- YAG lasers (532 nm). For haemangiomas diode lasers are prefered due to larger penetration depth

11. Center for Biomedical Optics and New Laser Systems L.R.Lindvold - 20/05/2015 EVAPORATION Water is heated adiabatic. The cells are disrupted. High laser power.

12. Center for Biomedical Optics and New Laser Systems L.R.Lindvold - 20/05/2015 PHOTOINDUCED PLASMA Very high power densities > 10 GW/cm 2 can easilily be acheived by pulsed lasers. Application areas: ! Eye surgery (post cataract and narrow angle glaucoma) ! Ear nose throat ! Lithotripsy (destruction of kidney stones)

13. Center for Biomedical Optics and New Laser Systems L.R.Lindvold - 20/05/2015 SIMPLE MATH Nd-YAG LASER 10 mJ Pulse energy with a duration of 10 ns yields 1 MW peak power Focused to 30 micron gives 141 GW/cm 2 Poyntings vector: Converted into field strength: E = 1.03 GV/m or 10.3 MV/cm !

14. Center for Biomedical Optics and New Laser Systems L.R.Lindvold - 20/05/2015 PHOTOINDUCED PLASMA OPTICAL EFFECTS ! All known non-linear effects can be observed ! Problems with plasma shielding

15. Center for Biomedical Optics and New Laser Systems L.R.Lindvold - 20/05/2015 PHOTOINDUCED PLASMA Treatment of post cataract due to IOL transplant Treatment of small/narrow angle glaucoma

16. Center for Biomedical Optics and New Laser Systems L.R.Lindvold - 20/05/2015 PHOTOABLATION High power pulsed UV-lasers Photodissociation of organic molecules. Short pulse 10 ns; no heating of the tissue. Facilitates "laser-etching" of tissue Depth of absorption typically 1  m Application areas: ! “Sculpting” the cornea ! Angioplasty

17. Center for Biomedical Optics and New Laser Systems L.R.Lindvold - 20/05/2015 PHOTOREFRACTIVE KERATECTOTMY (PRK) High power UV laser sculps the cornea by ablation Eye after treatment with PRK www.lasik1.com

18. Center for Biomedical Optics and New Laser Systems L.R.Lindvold - 20/05/2015 LASIK (LASER ASSISTED IN-SITU KERATOMILEUSIS)

19. Center for Biomedical Optics and New Laser Systems L.R.Lindvold - 20/05/2015 IN-SITU FLUORESCENCE SPECTROSCOPY OF TISSUE (OPTICAL BIOPSY) SCREENING OF SKIN CANCER Preliminary experiments have shown that the spectral signature of healthy tissue differs from that of cancerous tissue. However, large variations in the spectra from patient to patient, requires complicated data treatment.

20. Center for Biomedical Optics and New Laser Systems L.R.Lindvold - 20/05/2015 ULTRA FAST SPECTROSCOPY Some photochemical reactions are so fast that ordinary spectroscopy can’t be used. ! The visual process ! The photosynthesis ! Ion mobility in cellular membranes These processes can be studied by pico and femto second lasers.