Laser Applications in
Medicine
Judith Dawes,
MQ Photonics, Dept of Physics,
Macquarie University, Sydney.
LaserFest 2010
We are celebrating the 50th 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.
What are some properties of
laser light?
What are some properties of
laser light?
Light bulb
Laser light
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
What does a laser look like?
Why are lasers useful for medical
applications?
Why are lasers useful for medical
applications?
• 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
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.
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
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
Absorption by water
Water Absorption Spectrum
Absorption by melanin
and blood
Absorption of melanin and blood
Yellow lasers for retinal eye surgery
MQPhotonics Yellow laser
Yellow light absorbed by
haemoglobin to
coagulate blood vessels
of retina
Portwine Birthmark Treatment
Yellow laser to
fade birthmark
by treating
surface blood
vessels in skin
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
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
Conventional Microsurgery – to repair a
severed nerve or blood vessel
Stitching under a
microscope - Fine sutures
join nerves or blood vessels.
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
Laser Tissue Repair
Laser-activated protein solder
• protein strip joins tissue and
coagulated with laser light
• green dye absorbs laser
energy and heats protein
Laser-activated protein solder treated rat tibial nerve
• protein strip protects tissue
from heat damage and
strengthens tissue join
• natural body protein so no
“foreign body” reaction
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
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
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.
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
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.
©1998 A.D.A.M.
Software, Inc.
Need pulsed laser to produce
high-peak-power vapourisation
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.
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.
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
Laser beam
K-type
thermocouple
To data logger
Results
Sharp crater edges, no collateral damage.
Ablation rate ~ 1x10-3 mm3s-1
Temperature rise less than 2 oC.
Chris Artlett
Andrei Rode
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.
Thank you for listening!
Any questions?