Laser in Medicine Neurosurgery Er YAG Student Luis

Laser in Medicine Neurosurgery Er: YAG Student: Luis R. Castillo Professor: Ph. D. Carlos Treviño INAOE 1 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 Laser System in Neurosurgery Complication in the use of Laser System Conclusion Bibliography 2 04/22/04

Introduction Light has been used for diagnostic and therapy procedures t h r o u g h o u t t h e y e a r s. G r e e k s a n d A n c i e n t R o m a n s E g y p t 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. 3 04/22/04

Introduction One of the first attempts for diagnostic propose was the development of optical instruments to look: E E M o u t h y e s a r s e t c. . . 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, t o v i e w 4 04/22/04

Introduction The new integrated systems such as: L a s e r C a t h e t e r , L a s e r e n d o s c o p e F i b e r s c o p e e t c. . They have been the cause of revolution in many fields o f m e d i c i n e s u c h a s : Cardiov O d O p h N ascular o n t h a l m e u r o diseases o l o g y , l o g y. 5 04/22/04

Laser Physics Laser versus Ordinary Light Source Property Laser Ordinary light source Directionality Collimated (parallel beam) 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 Non collimated (light emitted in all directions) Medium or low Temporal Can produce very short and energetic pulses Typically long and low energy pulses Power density High; can be focused to a low; relatively large focal spot very small spot (of diameter d =l a m b d a ) 6 04/22/04

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

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 8 04/22/04

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

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

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

Laser Physics A basic illustration of the allowed photon emission processes Energy n 0 l =1 l =2 l =3 5 5 s 4 4 s 5 p 5 d 5 f 4 p 4 d 4 f 3 3 s 3 p 3 d 2 2 s 13. 6 e. V l 2 p Photon 1 1 s 12 04/22/04

Laser Physics Example of an energy diagram for Er 3+ ion in the glass fiber medium Energy of the Er 3+ ion in the glass fiber 1. 27 e. V E 3 Non radiative decay 980 nm Pump 0. 80 e. V 1550 nm E 2 Out In 0 1550 nm E 1 13 04/22/04

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

Laser Physics Program 0. 25 Laser Er: YAG 0. 2 0. 15 g 0 i 0. 1 0. 05 The program computes the energy and the width of the emitted pulse by a laser Er: YAG 0 0 5 10 Trti 15 10 Trti 20 15 0. 02 Erti 0. 015 0. 01 0. 005 5 20 15 04/22/04

Laser Physics Gain Medium Parameters 16 04/22/04

Laser Physics Pump Laser Parameters 2 W High Power Laser Diode 810 ± 10 17 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 18 04/22/04

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. TEMoo TEM 1 o TEMo 1 TEM 11 19 04/22/04

Laser Physics Real Beam Profile 20 04/22/04

Medical Laser Popular Lasers 21 04/22/04

Medical Laser Some Medical Applications of Lasers Field Power Duration Density Diagnosis Very low Therapy Depth of Penetration Long Shallow Low Medium Long Deep High Surgery High V. High Short Long V. Short Shallow Medical Example Application Blood diagnosis He. Cd T i s s u e C h a r a c t. Bio stimulation Tissue welding Blood coagulation Laser hyperthermia Phototherapy Laser lithotrispy Cutting Ablation without thermal damage He. Ne Nd: YAG Ar ion Nd: YAG Au vapor Dye CO 2 Excimer Er: YAG 22 04/22/04

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 23 04/22/04

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

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

Interaction of Laser Beam and 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 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 The material removal rate is given u 26 04/22/04

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. 27 04/22/04

Thermal Interaction between Laser and Tissue Spatial and temporal change of T (Eq. 1) (Eq. 2) 28 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: when the last function is substituted in Eq. 1, it may be solved numerically for each irradiation conditions such as: 29 04/22/04

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 30 04/22/04

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

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

Laser System in Neurosurgery 33 04/22/04

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. 34 04/22/04

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. 35 04/22/04

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. 36 04/22/04

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

Bibliography [1] Abraham Katzir, Laser and Optical Fibers in Medicine, Academic Press. , [2] Kuo Cheng Effects of Laser Pulse Shape and Beam Profile OEIT, Ph. D 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/Lanth. Act/lanthact. html 1997 8 [11] Manuel Forcales Fernandez, Two Color Spectroscopy of Energy Transfers in Si: Er Ph. D, Thesis 38 04/22/04

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 39 04/22/04