1. Laser Applications in Medicine Judith Dawes, MQ Photonics, Dept of Physics, Macquarie University, Sydney.

2. LaserFest 2010 We are celebrating the 50 th anniversary of the first laser this month. There will be laser-themed activities including workshops and a competition for school students during the next year! http://www.physics.mq.edu.au/laserfestsydney/ Ted Maiman built the laser with a ruby crystal, surrounded by a coiled flashlamp.

3. What are some properties of laser light?

4. Light bulb Laser light

5. What are some properties of laser light? Single colour (monochromatic) Directed beam Coherent (all waves lined up together) Can be continuous wave or pulsed output

6. What does a laser look like?

7. Why are lasers useful for medical applications?

8. Deliver energy to a target tissue Light can be delivered directly to specific cells or molecules Light can be delivered by optical fibre inside the body Laser light can cauterise (heat and seal) blood vessels to reduce bleeding during surgery or dental treatment

9. Laser-Tissue Interactions 3 main processes: Photo-thermal: heat generated in tissue causes a change in tissue, e.g. tissue welding or cell death Photo-chemical: chemical reaction in tissue caused by the energy of laser photons, e.g. laser photodynamic cancer therapy Photo-mechanical: acoustic wave generated by sudden heating of tissue leads to a shock wave and mechanical disruption of tissue e.g. destruction of kidney stones.

10. Laser- Tissue Interactions 2 Most effects are due to HEAT…. Laser light is absorbed by tissues and heats the tissues Tissue may be: Ablated (removed) – high power and energy Charred Coagulated (cooked or welded) “Biostimulated” – low power and energy

11. What absorbs the laser light? Tissues contain water and other molecules that absorb laser light Water absorbs infrared radiation Melanin is the brown pigment in skin, which absorbs blue-green light Blood contains haemoglobin, which is red, so it absorbs green/yellow light

12. Water Absorption Spectrum Absorption by water

13. Absorption of melanin and blood Absorption by melaninand blood

14. Yellow lasers for retinal eye surgery MQPhotonics Yellow laser Yellow light absorbed by haemoglobin to coagulate blood vessels of retina

15. Portwine Birthmark Treatment Yellow laser to fade birthmark by treating surface blood vessels in skin

16. Lasers for microsurgical tissue repair Tissues severed or cut need to be rejoined – usually sutured. Lasers can weld or join tissues instead of sutures Heat coagulates the proteins in the tissues Body tissues regenerate around the “weld” to strengthen it

17. Nerve repair after injury Nerve fibres consist of axons surrounded by an insulator (myelin sheath) When cut, the nerve regrows from the cell nucleus to the tip

18. Conventional Microsurgery – to repair a severed nerve or blood vessel Stitching under a microscope - Fine sutures join nerves or blood vessels.

19. Protein Solder Strips to Repair Peripheral Nerves Solid protein solder strips to repair solid tissues e.g. nerves Apply across join Laser light delivered by optical fibre to heat solder and bond with tissue

20. Laser Tissue Repair Laser-activated protein solder protein strip joins tissue and coagulated with laser light green dye absorbs laser energy and heats protein protein strip protects tissue from heat damage and strengthens tissue join natural body protein so no “foreign body” reaction Laser-activated protein solder - treated rat tibial nerve

21. Sleeve (Fold and Bond) Technique Repair tubular tissues eg blood vessels Maintain continuity of inner surface of vessel Apply laser energy through tissue to bond to solder

22. Advantages of lasers for medical applications Target absorption of specific tissues using specific colours of laser light Deliver energy (light and heat) directly to tissues Control heating of tissues to achieve different effects Delivered using optical fibre for small spaces

23. Research is a team effort! My research students working on this topic include: Rod Trickett, Antonio Lauto, Karen McNally, Bronwen Taylor, Peter Dekker, Chris Artlett, Ben Kwok, Thang (Peter) Ha. My collaborators working on this topic include: Dr David Knowles, Prof Jim Piper, Prof Earl Owen, Dr Peter Maitz, Dr Ambrose Chan, Prof Barrie Gillings, Prof Barry Luther-Davies, Dr Andrei Rode. Funding from the Australian Research Council, Macquarie University, Australian Dental Research Foundation, Microsearch Foundation.

24. Lasers for Dentistry Applications for treatment of hard tissues – carious enamel (tooth decay) and for operating on soft tissues (gums and mouth cavity) Potentially no pain because there is no vibration (compared with mechanical drill) Can target tooth decay or damaged tissue accurately Delivery by optical fibre for ease of access to the patient’s mouth

25. Lasers for Treatment of Dental Caries Which laser should we use to remove decay? Variety of IR and visible lasers have been used. Current dental lasers usually produce 3 μm wavelength light, absorbed by water. Need pulsed laser to produce high-peak-power vapourisation ©1998 A.D.A.M. Software, Inc.

26. Conventional Laser Ablation Ablation with long laser pulses requires water cooling to minimise heating of the nerve in the tooth and avoid collateral damage. Material removal occurs by heating, which then vapourises the tooth surface.

27. Use Femtosecond (10 -13 s pulsewidth) Laser Ablation Excellent surface preparation to enable permanent attachment of fillings, with no microcracking (to avoid infection) and precise ablation. Minimise heating effects. Only 5.5  C temperature rise damages the nerve. Femtosecond laser ablation of teeth can give cleaner features with no collateral damage, and negligible heating of tooth.

28. Experimental Setup Extracted human teeth (not in patient’s mouth) with thermocouple to monitor tooth temperature. Laser pulses with wavelengths of 800 nm and 400 nm K-type thermocouple To data logger Laser beam

29. Results Sharp crater edges, no collateral damage. Ablation rate ~ 1x10 -3 mm 3 s -1 Temperature rise less than 2 o C. Andrei Rode Chris Artlett

30. Conclusions Lasers have many advantages for medical and dental treatments. Lasers can selectively deliver energy as heat to tissues, and can ablate or bond tissues, or denature proteins in cells, in a non-contact manner. Optical fibres can deliver laser light conveniently to the operative site.

31. Thank you for listening! Any questions?