Upload
lamar-blaylock
View
218
Download
4
Tags:
Embed Size (px)
Citation preview
1
Laser in MedicineNeurosurgery
Er:YAG
Student: Luis R. CastilloProfessor: PhD. Carlos Treviño
INAOE
04/22/04
2
• Introduction• Laser Physics• Medical Laser• Interaction of Laser Beam and Material• Laser Interaction with Tissue• Thermal Interaction between Laser and
Tissue• Laser System in Neurosurgery• Complication in the use of Laser System• Conclusion• Bibliography
04/22/04
Agenda
3
- Light has been used for diagnostic and therapy proceduresthroughout the years.
Greeks and RomansAncient Egypt
- It was clearly understood by physics and doctors that the patients would benefit enormously if they diagnosed and treated the diseases of the patients, in side or out side of their body, using non surgical instruments.
04/22/04
Introduction
4
- One of the first attempts for diagnostic proposewas the development of optical instruments to look:
EyesEarsMouth etc...
- With the availability of lasers, laser crystals, fiber optic. A complex instruments became a powerful tools for medical applications
- An example is the endoscope integrated system.From the Greek endo means within and skopien,to view
04/22/04
Introduction
5
- The new integrated systems such as:
Laser Catheter,Laser endoscopeFiberscope etc..
- They have been the cause of revolution in many fieldsof medicine such as:
Cardiovascular diseasesOdonthologyOphthalmology,Neurology.
04/22/04
Introduction
6
04/22/04
Laser Physics
Property Laser Ordinary light source
Directionality Collimated (parallel beam) Non collimated (light emitted in all directions)
Color Monochromatic (one color) Polychromatic (many colors)Comment: coherent beam Comment: non coherent beam(i.e., ordered in time & space) (i.e., non ordered)
Power output Can be high Medium or low
Temporal Can produce very short and Typically long and low-energyenergetic pulses pulses
Power density High; can be focused to a low; relatively large focal spotvery small spot (of diameterd=lambda)
Laser versus Ordinary Light Source
7
04/22/04
Laser Physics
Comparison of a Laser and an ordinary light source
Coherent(in space and time) Non coherent
inte
nsit
y
Monochromatic Polychromatic
I I
inte
nsit
y
Collimated beam Divergent beam
laser Ordinary lamp
8
04/22/04
Laser Physics
CW and pulsed laser beams
Time
PowerContinuous wave (CW)
Time
Power
Time
Power
Long pulses, high rep rate, low peak power
Short pulses , low rep rate, high peak power
9
04/22/04
Laser Physics
Schematic drawing of the laser
Pump Fiber (as a gain medium)
LASER
Pump
Crystal (as a gain medium) LASER
Pump
or Pump
10
04/22/04
Laser Physics
Atomic transitions
Absorption
inte
nsit
y
I I I
hE
in
hE
o
out
Spontaneous emission Stimulated emission
E2E
1E
2N
1N
11
04/22/04
Laser Physics
3 level and 4 level
population
Upperlevel
EnergyLevel
Pump Band
Lowerlevel
UpperlevelEnergy
Level
population
Pump Band
Ground
level
Lowerlevel Ground
level
Relax
12
04/22/04
Laser Physics
A basic illustration of the allowed photon emission processes
Energy0
1s1
2s 2p2
3s 3p3 3d
4s 4p4 4d 4f
5s 5p5 5d 5f
= 0 = 1 = 2 = 3
13.6eV
n
Photon
13
04/22/04
Laser Physics
Example of an energy diagram for Er3+ ion in the glass fiber medium
Energy of the Er3+ ionin the glass fiber
E10
1.27 eV
0.80 eV E2
E3
1550 nm 1550 nm
InOut
980 nm
Non-radiative decayPump
14
04/22/04
Laser Physics
Example of an energy diagram for Erbium
15
04/22/04
Laser Physics
Program
The program computes the energy and the width of the emitted pulse by a laser Er:YAG
LASER RATE EQUATIONS
Accumulative build-up time
n1
1
g01
g01
Einj
Ep A c dt
n1
==> initial values
==> rate of change of inversion densityni 1
i 1
g0i 1
ni
1 2 c i dt
i 1 c ni
w1 dt
ni
==> rate of change of photon density
==> change in gain
0 5 10 15 200
0.05
0.1
0.15
0.2
0.25
g0i
Trti
5 10 15 20
0.005
0.01
0.015
0.02
0.025
Erti
Trti
Laser Er:YAG
16
04/22/04
Laser Physics
Gain Medium Parameters
17
04/22/04
Laser Physics
Pump Laser Parameters
2W High Power Laser Diode 810 ± 10
18
04/22/04
Laser Physics
Gain Medium
- Change of host material makes small differences in laser radiation frequency
- Change of dopant ion makes large changes in laser radiation frequency
19
04/22/04
Laser Physics
Beam
TEMo1
TEM11
TEMoo
TEM1o
Intensity distribution is not just a mathematical curiosity; it is extremely important for laser-tissue interaction and in particular for laser neurosurgery.
20
04/22/04
Laser Physics
Real Beam Profile
21
04/22/04
Medical Laser
Popular Lasers
22
04/22/04
Medical Laser
Field Power Duration Depth Medical Example
Density of Penetration Application
Diagnosis Very low Long Shallow Blood diagnosis HeCdTissue Charact.
Therapy Low Long Deep Bio stimulation HeNeMedium Long Medium Tissue welding Nd:YAG
Blood coagulation Ar ionMedium Long Deep Laser hyperthermia Nd:YAG
Phototherapy Au vaporHigh Short Laser lithotrispy Dye
Surgery High Long Shallow Cutting CO2V. High V. Short Shallow Ablation without Excimer
thermal damage Er:YAG
Some Medical Applications of Lasers
23
Ir reflected irradiance
Is scattered irradiance
Ia absorbed irradiance
It transmitted irradiance
Ii = Ir + Is + Ia +It
04/22/04
Interaction of Laser Beam and Material
Transmission of laser beams through materials
2
1
1
n
n
Ii
IrxeIxI )0()(
xeIxI )0()(
24
04/22/04
Interaction of Laser Beam and Material
Laser beams through materials
25
04/22/04
Interaction of Laser Beam and Material
Absorption not always result in generation of heat
26
04/22/04
Interaction of Laser Beam and Material
Material processing by laser beams
- If heating effects of laser beam are take place
- If the scattering effect are ignored
- If the beam is totally absorbed in a distance L
- If the laser beam is applied for a period t
- If thermal losses are ignored
- If mechanics heat transfer is viewed as macroscopic - The material removal rate is given u
HTc
I
dt
dxu
u = vaporization rate p = density of the materialdx = layer thicknessI = power density ( irradiance)c= heat capacity T= change of temperatureH = latent heat of vaporization
27
- It has been the subject of extensive
experimental and theoretical work ( Welch 1984, 1991; Mckenzic
1990; Jacques 1993,1996).
- Er:YAG lasers showed minimal thermal damage When a sample is heated by a heat source, its temperature T rises and it is possible to calculate the spatial and temporal change of T.
04/22/04
Thermal Interaction between Laser and Tissue
Thermal damage
28
04/22/04
Thermal Interaction between Laser and Tissue
Spatial and temporal change of T
ctZYXQtZYXTktZYXt
T /,,,,,,,,, 2
cv cs
danvqdvt
q
t
Q )(
(Eq.1)
(Eq.2)
29
04/22/04
Thermal Interaction between Laser and Tissue
Additional assumptions….
-If one dimensional case is ….
-If flat sample whose surface is the xy plane
-If A Gaussian laser beam is directed a long z axis
- in this case the absorbed energy generates heat and rate of heat is given by:
Iz
IQ
when the last function is substituted in Eq. 1, it may be solved numerically for each irradiation conditions such as:
30
-Laser wavelength for which there is deep penetration into tissue and strong scattering.
- Laser wavelength that are strongly absorbed with no scattering
- Long pulses (or CW) , where heat dissipation occurs via conduction during the pulse
- Short pulses where there is practically no dissipation during the pulse
04/22/04
Thermal Interaction between Laser and Tissue
Additional assumptions….
T(z,t) rises quickly to a final value Tm that is proportional to the deposited energy
31
04/22/04
Thermal Interaction between Laser and Tissue
Tissue effects
32
04/22/04
Thermal Interaction between Laser and Tissue
Tissue effects
33
04/22/04
Laser System in Neurosurgery
34
- The laser beam may be focused to a small area, it is possible view it by a integrated Microscope.
- The focal spot is easily moved with a mirror or lens system.
- The laser beam vaporizes or coagulates tissue in the target area without mechanical Contact and damage to adjacent areas.
- Laser radiation has been used to vaporize tumors in sensitive locations in the brain.
- Once the exact location of such tumors is determined by scan system (CT or MRI) , include deeply tumors, can be treated successfully.
04/22/04
Laser System in Neurosurgery
Advantages
35
- Focusing a high power laser beam into a thin optical fiber presents a problem.
- An optical feedback and control mechanism that prevents damage at the output face of the fiber due to high power densities. - It is difficult to asses how much laser energy has reached a target tissue
and how much has actually been absorbed in the tissue.
04/22/04
Complication in the use of Laser System
Optical problems
36
- Optical fibers tend to break upon repeated bending.
- Thick optical fibers (power transmission) are a little bit difficult to use.
-The mechanical devices that connect fibers to holders or to attach the tips are still bulky in contrast with the thin catheters and endoscopes.
- Due to de above comment it can not be easily inserted and guided inside the body but must be inserted through guide wire.
- Exits difficult for angulations for the tips for a target point of view A cool system is needed to the power fibers sterilization is difficult.
04/22/04
Complication in the use of Laser System
Mechanical problems
37
04/22/04
Conclusion
Your own conclusion !!!
38
04/22/04
Bibliography
[1] Abraham Katzir, Laser and Optical Fibers in Medicine, Academic Press.
[2] Kuo-Cheng Cheng, Effects of Laser Pulse Shape and Beam Profile OEIT, PhD Thesis
[3] Max Born & Emil Wolf, Principles of Optics. Pergamon Press.
[4] Samuel C. Barden, Fiber Optics in Astronomy, Astronomical Society of the Pacific.
[5] Michael A. Morgan II, David V. Guerra,"An introduction to laser modeling studies with nitrogen pumped dye laser",Am. J. Phys. 67 (9), september 1999
[6] Carlos B. Roundy, Current Technology of Laser Beam Profile Measurements, Spiricon, Inc.
[7] Sony Corporation
[8] Saint-Gobain Crystals & Detectors KK Corporation
[9] Carlos Treviño, Laser Course Notes, http://www-optica.inaoep.mx/investigadores/dr_trevino.htm
[10] S.J. Heyes, http://www.chem.ox.ac.uk/icl/heyes/LanthAct/lanthact.html 1997-8
[11] Manuel Forcales Fernandez, Two Color Spectroscopy of Energy Transfers in Si:Er PhD, Thesis
39
• Introduction• Laser Physics• Medical Laser• Interaction of Laser Beam and Material• Laser Interaction with Tissue• Thermal Interaction between Laser and
Tissue• Fiber Optic Laser System in Neurosurgery• Complication in the use of Laser System• Conclusion• Bibliography
04/22/04
Questions or Comments