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Laser in Medicine Neurosurgery Er:YAG Student: Luis R. Castillo Professor: PhD. Carlos Treviño

Laser in Medicine Neurosurgery Er:YAG Student: Luis R. Castillo Professor: PhD. Carlos Treviño INAOE. 04/22/04. Agenda. Introduction Laser Physics Medical Laser Interaction of Laser Beam and Material Laser Interaction with Tissue Thermal Interaction between Laser and Tissue

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Laser in Medicine Neurosurgery Er:YAG Student: Luis R. Castillo Professor: PhD. Carlos Treviño

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  1. Laser in Medicine Neurosurgery Er:YAG Student: Luis R. Castillo Professor: PhD. Carlos Treviño INAOE 04/22/04

  2. Agenda • 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

  3. Introduction • - Light has been used for diagnostic and therapy procedures • throughout the years. • Greeks and Romans • Ancient 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

  4. Introduction • One of the first attempts for diagnostic propose • was the development of optical instruments to look: • Eyes • Ears • Mouth 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

  5. Introduction • The new integrated systems such as: • Laser Catheter, • Laser endoscope • Fiberscope etc.. • They have been the cause of revolution in many fields • of medicine such as: • Cardiovascular diseases • Odonthology • Ophthalmology, • Neurology. 04/22/04

  6. Laser Physics Laser versus Ordinary Light Source PropertyLaserOrdinary 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-energy energetic pulses pulses Power density High; can be focused to a low; relatively large focal spot very small spot (of diameter d=lambda) 04/22/04

  7. Laser Physics Comparison of a Laser and an ordinary light source laser Ordinary lamp Collimated beam Divergent beam I I intensity intensity Monochromatic Polychromatic Coherent (in space and time) Non coherent 04/22/04

  8. Laser Physics CW and pulsed laser beams Continuous wave (CW) Power Time Long pulses, high rep rate, low peak power Power Time Short pulses , low rep rate, high peak power Power Time 04/22/04

  9. Laser Physics Schematic drawing of the laser Fiber (as a gain medium) Pump LASER Pump Crystal (as a gain medium) or Pump LASER Pump 04/22/04

  10. Laser Physics Atomic transitions I I I intensity Absorption Spontaneous emission Stimulated emission 04/22/04

  11. Pump Band Pump Band Upper level Upper level Energy Level Energy Level Lower level Lower level Ground level Ground level population population Laser Physics 3 level and 4 level Relax 04/22/04

  12. E n e r g y = 2 = 3 = 0 = 1 l l l l 0 l n 5 p 5 s d f 5 5 5 4 p 4 s d f 4 4 4 3 p 3 3 s 3 d P h o t o n 2 s p 2 2 e V ­ 1 3 . 6 1 s 1 Laser Physics A basic illustration of the allowed photon emission processes 04/22/04

  13. + 3 E n e r g y o f t h e E r i o n i n t h e g l a s s f i b e r E 1 . 2 7 e V 3 N o n - r a d i a t i v e d e c a y P u m p 9 8 0 n m 0 . 8 0 e V E 2 1 5 5 0 n m 1 5 5 0 n m O u t I n E 0 1 Laser Physics Example of an energy diagram for Er3+ ion in the glass fiber medium 04/22/04

  14. Laser Physics Example of an energy diagram for Erbium 04/22/04

  15. Laser Er:YAG 0.25 0.2 0.15 g0 i 0.1 0.05 0 0 5 10 15 20 Trt i 0.025 0.02 0.015 Ert i 0.01 0.005 5 10 15 20 Trt i Laser Physics Program The program computes the energy and the width of the emitted pulse by a laser Er:YAG 04/22/04

  16. Laser Physics Gain Medium Parameters 04/22/04

  17. Laser Physics Pump Laser Parameters 2W High Power Laser Diode 810 ± 10 04/22/04

  18. 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 04/22/04

  19. TEMoo TEMo1 TEM1o TEM11 Laser Physics Beam Intensity distribution is not just a mathematical curiosity; it is extremely important for laser-tissue interaction and in particular for laser neurosurgery. 04/22/04

  20. Laser Physics Real Beam Profile 04/22/04

  21. Medical Laser Popular Lasers 04/22/04

  22. Medical Laser Some Medical Applications of Lasers FieldPower DurationDepth Medical Example Densityof PenetrationApplication Diagnosis Very low Long Shallow Blood diagnosis HeCd Tissue Charact. Therapy Low Long Deep Bio stimulation HeNe Medium Long Medium Tissue welding Nd:YAG Blood coagulation Ar ion Medium Long Deep Laser hyperthermia Nd:YAG Phototherapy Au vapor High Short Laser lithotrispy Dye Surgery High Long Shallow Cutting CO2 V. High V. Short Shallow Ablation without Excimer thermal damage Er:YAG 04/22/04

  23. Interaction of Laser Beam and Material Transmission of laser beams through materials • Ir reflected irradiance • Is scattered irradiance • Ia absorbed irradiance • It transmitted irradiance • Ii = Ir + Is + Ia +It 04/22/04

  24. Interaction of Laser Beam and Material Laser beams through materials 04/22/04

  25. Interaction of Laser Beam and Material Absorption not always result in generation of heat 04/22/04

  26. 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 u = vaporization rate p = density of the material dx = layer thickness I = power density ( irradiance) c= heat capacity T= change of temperature H = latent heat of vaporization 04/22/04

  27. Thermal Interaction between Laser and Tissue Thermal damage • 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

  28. Thermal Interaction between Laser and Tissue Spatial and temporal change of T (Eq.1) (Eq.2) 04/22/04

  29. 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: when the last function is substituted in Eq. 1, it may be solved numerically for each irradiation conditions such as: 04/22/04

  30. Thermal Interaction between Laser and Tissue Additional assumptions…. • -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 T(z,t) rises quickly to a final value Tm that is proportional to the deposited energy 04/22/04

  31. Thermal Interaction between Laser and Tissue Tissue effects 04/22/04

  32. Thermal Interaction between Laser and Tissue Tissue effects 04/22/04

  33. Laser System in Neurosurgery 04/22/04

  34. Laser System in Neurosurgery Advantages - 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

  35. Complication in the use of Laser System Optical problems - 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

  36. Complication in the use of Laser System Mechanical problems • - 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

  37. Conclusion Your own conclusion !!! 04/22/04

  38. 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 04/22/04

  39. Questions or Comments • 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

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