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Center for Biomedical Opticsand New Laser Systems
L.R.Lindvold - 18/04/23
BIOMEDICAL APPLICATIONS OF LASERS; A REVIEW
LARS LINDVOLD
OVC ApS
CAT SCIENCE PARK
Center for Biomedical Opticsand New Laser Systems
L.R.Lindvold - 18/04/23
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
Center for Biomedical Opticsand New Laser Systems
L.R.Lindvold - 18/04/23
INTERACTIONS BETWEEN LIGHT AND TISSUE
Possible effects:
Photochemical
Thermal
Photoinduced plasma
Photoablation
Center for Biomedical Opticsand New Laser Systems
L.R.Lindvold - 18/04/23
ABSORPTIONS PROPERTIES OF TISSUE COMPONENTS
Center for Biomedical Opticsand New Laser Systems
L.R.Lindvold - 18/04/23
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)
Center for Biomedical Opticsand New Laser Systems
L.R.Lindvold - 18/04/23
EXAMPLE OF PDTThe bladder seen through an endoscope in white light
The bladder seen through endoscope with blue laser light after ALA5 treatment. Red fluorescence indicates tumor
Center for Biomedical Opticsand New Laser Systems
L.R.Lindvold - 18/04/23
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-photon 2-photon
Center for Biomedical Opticsand New Laser Systems
L.R.Lindvold - 18/04/23
COAGULATION (60-100 OC)
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)
Center for Biomedical Opticsand New Laser Systems
L.R.Lindvold - 18/04/23
PHOTOCOAGULATION (1)
Haemorrhaging on the retina
Fundus image of Retina after laser treatment
Laser ofthalmoscope for photocoagulation
Center for Biomedical Opticsand New Laser Systems
L.R.Lindvold - 18/04/23
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
Center for Biomedical Opticsand New Laser Systems
L.R.Lindvold - 18/04/23
EVAPORATION
Water is heated adiabatic. The cells are disrupted.
High laser power.
Center for Biomedical Opticsand New Laser Systems
L.R.Lindvold - 18/04/23
PHOTOINDUCED PLASMA
Very high power densities > 10 GW/cm2 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)
Center for Biomedical Opticsand New Laser Systems
L.R.Lindvold - 18/04/23
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/cm2
Poyntings vector:
S ExH S E0
0
2
4
Converted into field strength: E = 1.03 GV/m
or 10.3 MV/cm !
Center for Biomedical Opticsand New Laser Systems
L.R.Lindvold - 18/04/23
PHOTOINDUCED PLASMA OPTICAL EFFECTS
All known non-linear effects can be observed
Problems with plasma shielding
Center for Biomedical Opticsand New Laser Systems
L.R.Lindvold - 18/04/23
PHOTOINDUCED PLASMA
Treatment of post cataract due to IOL transplant
Treatment of small/narrow angle glaucoma
Center for Biomedical Opticsand New Laser Systems
L.R.Lindvold - 18/04/23
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
Center for Biomedical Opticsand New Laser Systems
L.R.Lindvold - 18/04/23
PHOTOREFRACTIVE KERATECTOTMY (PRK)
High power UV laser sculps the cornea by ablation
Eye after treatment with PRK
www.lasik1.com
Center for Biomedical Opticsand New Laser Systems
L.R.Lindvold - 18/04/23
LASIK(LASER ASSISTED IN-SITU KERATOMILEUSIS)
Center for Biomedical Opticsand New Laser Systems
L.R.Lindvold - 18/04/23
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.
Center for Biomedical Opticsand New Laser Systems
L.R.Lindvold - 18/04/23
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.