Medical Lasers. UCONN BME 5040 Medical Instrumentation in the Hospital Frank Painter. Introduction

Transcription

1 Medical Lasers UCONN BME 5040 Medical Instrumentation in the Hospital Frank Painter Introduction LASER is an acronym, which stands for: Light Amplification by Stimulated Emission of Radiation 2 1

2 Basic Laser Principles Laser light is a form of electromagnetic radiation Lasers produce light by a process that involves changes in energy states within the atoms of certain materials. Atoms that have been promoted to higher energy states release this energy in the form of light by a process called stimulated emission. The laser light is amplified by reflecting it back and forth in the lasing medium with a pair of mirrors. The laser light is then released in a stream or pulse through the partially transmitting mirror at one end of the cavity. The color of laser light is normally expressed in terms of the laser's wavelength. The most common unit used in expressing a laser's wavelength is a nanometer (nm). 3 Lasers Laser light is collimated, coherent and monochromatic That is all light waves moving in the same direction with one frequency and wavelength Focused to produce a very high power density ION lasers use electromagnetic energy to produce and confine the ionized gas plasma which serves as the lasing medium. Lasers can be continuous wave (CW) or pulsed (where flashlamps provide the pulse) Laser efficiency is variable - argon ion lasers are about 0.01% efficient (1 W needs 10KW power) 4 2

3 Ordinary Light Multiple wavelengths (asynchronous) Multidirectional Incoherent 5 Monochromatic (synchronous) Directional Coherent Laser Light Lasers can focus a large amount of energy into a small area, thereby creating a much greater hazard than ordinary light 6 3

4 Components of a Laser The optical cavity contains the media to be excited with mirrors to redirect the produced photons back along the same general path. The pumping system uses photons from another source such as a xenon gas flash tube (optical pumping) to transfer energy to the media, electrical discharge within the pure gas or gas mixture media (collision pumping), or relies upon the binding energy released in chemical reactions to raise the media to the metastable or lasing state. The laser medium can be a solid (state), gas, dye (in liquid), or semiconductor. Lasers are commonly designated by the type of lasing material employed. 7 Lasing Materials Solid state lasers lasing material distributed in a solid matrix A fiber doped with erbium, neodymium-yag (yttrium aluminum garnet) lasers. neodymium-yag laser emits infrared light at 1064 nm Gas lasers helium and helium-neon, HeNe, - most common gas laser HeNe has a primary output of a visible red light. CO2 lasers emit energy in the far-infrared, 10.6 micrometers, and are used for cutting hard materials. Argon lasers 458nm, 488 nm & 514 nm - absorbed by red materials 8 4

5 Excimer lasers Lasing Materials name is derived from the terms excited and dimers uses reactive gases such as chlorine and fluorine mixed with inert gases such as argon, krypton, or xenon. When electrically stimulated, a pseudomolecule or dimer is produced and when lased, produces light in the ultraviolet range. Dye lasers use complex organic dyes like rhodamine 6G in liquid solution or suspension as lasing media. tunable over a broad range of wavelengths. 9 Semiconductor lasers Lasing Materials sometimes called diode lasers, are not solidstate lasers. These electronic devices are generally very small and use low power. may be built into larger arrays, e.g., the writing source in some laser printers, compact disk players, bar code readers, fiber optic communications, directional lighting, laser light shows, and dentistry Most common type of laser in general times more of this type sold than all other types combined. 10 5

6 Types of Lasers Lasing media types Gas, liquid, solid, semiconductor, dye Length of time the beam is active Continuous wave, pulsed, Q-switched 11 Medical Lasers 12 6

7 Medical Lasers 13 Aiming Beam Helium-Neon (He-Ne) Laser Red in color Commonly used in pointers and scanners Minimal physical effects (except high power in the eye) Aiming beam Coincident with other invisible laser beam Used to so you know where the invisible laser beam will cut or coag before you activate it 14 7

8 Medical Applications Cardiology Cardiothoracic Surgery Dentistry Dermatology Emergency Medicine Gynecology Neurosurgical Ophthalmic Plastic surgery Surgical Urology Vascular angioplasty cancer diagnosis cancer treatment hair & tattoo removal dermatology lithotripsy mammography medical imaging microscopy prostatectomy tissue ablation 15 Surgical Lasers CO 2 lasers Nd:Yag Argon KTP Erbium Holmium:Yag Ruby Pulsed Dye Copper Vapor Diode Excimer Intensed Pulsed Light (IPL) 16 8

9 CO 2 Lasers 10.6 μm (10,600 nm) far infrared range Beam is invisible Can be stopped by glass or plastic beam is dispersed by simple safety goggles or window glass Can be reflected off shiny surfaces (mirrors) The articulating arm on a CO 2 laser is a series of tubes with mirrors at the elbows. Water readily absorbs energy of this wavelength

10 CO 2 Lasers Cutting (e.g. incisions, excising tissue) Vaporization of tissue (e.g. tumors, warts) Primarily surface (visible) work Some use with rigid scopes or special flexible scopes Free-beam (hand held) Reduced trauma, preserves adjacent tissue More easily maintains sterility 19 CO 2 Lasers Gynecology Abdominal adhesions, tubal reconstruction, endometriotic excisions, vaporization Otolaryngology Airway obstructions, tracheal stenoses, vocal cord papillomas, oral tumors, laryngeal lesions Plastic, dental, orthopedic and cardiovascular surgery Neurosurgery micromanipulator & surgical microscope 20 10

11 Continuous Wave (CW) CO 2 Lasers Press the foot pedal and get a continuous delivery of energy Highest average power, least precise For cutting and vaporization Superpulse, Ultrapulse 200 to 1000 μsec pulses at very high energy levels 21 Laser tube Laser pump CO 2 Lasers - Components Cooling system (some are water cooled) Aiming laser Some laser tubes are sealed, some employ continuously flowing CO 2 Mirrored articulating arm Flexible CO 2 waveguides 22 11

12 CO 2 Laser Safety Serious eye injury resulting from inappropriate eye protection Fire risk when used near O 2 or N 2 O sources CO 2 Laser resistant tracheal tubes Excessive bleeding requiring an ESU nearby CO 2 laser cannot coagulate Smoke evacuation to improve visibility and reduce noxious and dangerous plumes 23 CO 2 Reflection 24 12

13 CO 2 Vaporization 25 ECRI s Ideal CO 2 Laser Variable 1 to 30 watts (minimum) Pulse width > 0.01 sec Sealed gas filled laser tube Internal air-cooling system CW and pulsatile modes Appropriate power connections in room (240 VAC, water cooling for high power CO 2 ) 26 13

14 Other interesting facts CO2 Lasers Very high power levels available Frequently used for industrial lasers Used to cut hundred micrometer channels in plastic for microfluidic devices Soviets designed a megawatt CO2 laser as an orbit to orbit weapon 27 Nd:YAG Lasers Neodymium: yttrium-aluminum-garnet 1064 nm near infrared (invisible) Frequency doubled KTP / 532 (potassium titanyl phosphate) - green Q-switched Penetrates tissue more deeply than most other lasers Photocoagulates at low power densities Vaporizes tissue at high power densities 28 14

15 Gastroenterology Urology Gynecology General surgery Dentistry Dermatological lasers Nd:YAG Lasers Prostatic ablation systems (frequency doubled-532nm) Endometrial ablation systems 29 Nd:YAG Lasers Can be delivered through flexible silica fibers and can pass through clear fluids, unpigmented tissue and the top layer of the skin Minimal tissue absorption, maximum penetration (up to 1 cm) Destroys tissue by photothermal destruction Controls excessive bleeding (uterine and gastrointestinal) by coagulation Destroys inoperable highly vascular tumors of the respiratory tract, stomach, brain, prostate, rectum and bladder 30 15

16 31 Nd:YAG Lasers Surgical Nd:YAG lasers are high power continuous wave photoablation (measured in seconds and joules) Opthalmic Nd:YAG lasers produce short pulse low energy photodisruptive effect (measured in nanoseconds & millijoules) Frequency doubled Nd:YAG passed through a KTP crystal produces a green laser that is absorbed by pigmented tissue to a depth of 1 to 2 mm for use in otolaryngology, gynecology and dermatology 32 16

17 Nd:YAG Lasers Nd:YAG requires a He-Ne aiming beam KTP requires a low power KTP aiming beam Highly inefficient electronics which create much heat and require internal cooling systems Some fibers have a special sapphire tips that heat up and are used to contact and burn Fibers are small and can be threaded into endoscopes into confined body cavities Some fibers have focusing lenses on the end or are designed for direct contact with the tissue 33 Nd:YAG Laser Safety Very dangerous if eye contact is made Eye s lens focus the laser to the retina Requires special safety glasses (wavelength specific) Because of tissue penetration adjacent tissue or tissue below the surface can be inadvertently damaged with little or no apparent surface tissue effect. Accidental organ perforations when unintended instrument crosses the path of the laser and the beam is deflected

18 Nd:YAG Laser Safety Fire hazard when used in the presence of O 2 or N 2 O Laser resistant trach tubes Smoke evacuators are required Ignition of methane bowel gas Abdominal endoscopic surgery in the presence of laser cooling gas has caused embolisms Contact tips may adhere to tissue and tear when pulled away 35 Nd:YAG Laser Safety Emission of audible tones during activation Visual activation indicators Interlocks that turn off beam when no fiber is connected Removable key to prevent unauthorized operation Indicator when cooling system malfunctions Fiber must be extended beyond end of endoscope to prevent scope damage 36 18

19 ECRI Recommends Contact lasers only need up to 40 watts Free-beam procedures may need w Must have output power meter Internal cooling system Allow manual fiber calibration Operate at 120 VAC vs 240 VAC or phase Laser technology committee needed to access policies, procedures, safety factors and purchasing issues 37 Before purchase consider: ECRI Recommends Clinical need Existing technology (other lasers, ESUs,...) Type and number of procedures Versatility of instrument Experience and preferences of surgeons Reimbursement for use Utility requirements (renovation needed?) Safety, reliability, service and cost of the system FDA 510K status of procedures 38 19

20 Nd:YAG Total Cost of Ownership Acquisition cost Maintenance cost Reusable fibers & Disposable fibers($200) Rent vs. purchase 39 Ho:YAG Lasers (Holmium: Yttrium-Aluminum-Garnet) Orthopedics Ophthalmology Otolaryngology Cardiology Urology Oral/maxillofacial Pulmonary medicine 40 20

21 Ho:YAG Lasers 2100 nm - near the absorption peak of water Cuts or ablates tissue with moderate hemostatsis, little charring and a thin zone of necrosis Delivered through a thin silica fiber that contacts tissue or is in close proximity ideal for endoscopic surgery Thin fibers enable access to narrow spaces Knees, wrists, Removal of torn ligaments, smoothing of rough cartilage without injuring nearby tissue, cut bone, open tear ducts, removal of kidney stones, endoscopic spinal disc removal Can cut through metal 41 Ho:YAG Lasers Active beam is invisible Requires an aiming beam Requires an internal cooling system Requires user knowledge of fiber repair. Cleaving and polishing fiber ends Testing fibers for cracks and power loss 42 21

22 Ho:YAG Lasers Can be used in lithotripsy Can ablate calculi and bone Fiber is placed on the kidney stone With each laser pulse heating occurs on the stone surface Water within is vaporized and fragmentation occurs in a drilling fashion Causes stress fractures in the stone and fragmentation Smaller fragments are then heated until all fragments are small enough to be passed or retrieved with a basket 43 Surgical Diode Lasers Relatively new Uses a diode as the lasing medium rather than a gas or crystal Cheaper to manufacturer In their infancy in medical applications Dental Liver surgery Prostate ablation Limitation has been power (most are single diode lasers & < 5 watts) 44 22

23 Surgical Diode Lasers 1992 lasers with diode arrays provided 15 to 60 watts and medical use began. Very efficient lower power consumption Much smaller and more compact Very reliable and less expensive to repair No mirrors, cooling systems or adjustments Lower cost than typical lasers (CO 2, Nd:YAG, Ho:YAG) Wavelengths 810 & 980 nm (Nd:YAG=1064nm) 45 Like CO2 lasers Ho:YAG is absorbed by water in tissue Majority of energy is absorbed superficially resulting in superficial cutting and ablation of tissue Comparing Lasers 46 23

24 Comparing Lasers Three zones of tissue damage are produced A crater from which vaporized tissue is ejected A zone of necrosis caused by boiling tissue A zone of coagulation caused by thermal denaturation of collagen Depth of these three zones CO 2 Laser 0.05 mm Ho:YAG Laser 0.5 mm Nd:Yag Laser 4.0 to 6.0 mm 47 Light Spectrum & Skin Depth 24

25 Comparing Lasers 49 Comparing Lasers CO 2 Precise cuts with very narrow zones of thermal damage, but no hemostasis in vascularized tissue Ho:YAG Precise cuts with adequate hemostasis during ablation Wavelength can be transmitted down fibers allowing endoscopic use 50 25

26 Comparing Lasers Excimer 193 (um) High resolution microsurgery, cardiac revascularization, LASIK & PRK Argon 488 & 514 Absorbed by hemoglobin, used in retinal surgery, removes birthmarks KTP 532 Cuts, absorbed by orange-yellow Pulsed Dye Preferred for vascular lesions & birthmarks Diode Laser hair removal and periodontal surgery, likely to replace all others Nd:YAG 1064 Deep penetration, coagulates tissue Ho:YAG 2070 Ablates bone, cartilage and stones Erbium 2940 Laser resurfacing of wrinkles CO Surgical Laser, most used, it cuts like a scalpel, can vaporize tissue 51 Comparing Lasers Excimer used to write this on a human hair 52 26

27 Laser Hazard Classes The ANSI Laser Safety standard has defined Laser Hazard Classes, which are based on the relative dangers associated with using these lasers. Least Hazardous Class 1 Class 2 Class 3a Class 3b Class 4 Most Hazardous 53 Class 1 Lasers This class cannot produce a hazardous beam because it is of extremely low power. or because it has been rendered intrinsically safe due to the laser having been completely enclosed so that no hazardous radiation can escape and cause injury

28 Class 2 Lasers These lasers are visible light ( nm) continuous wave or pulsed lasers which can emit energy greater than the limit for Class I lasers and radiation power not above 1 mw. This class is hazardous only if you stare directly into the beam for a long time, which would be similar to staring directly at the sun. Because class 2 lasers include only visible wavelengths, the aversion reaction will usually prevent us from permanently damaging our eyes. The aversion reaction refers to our tendency to look away from bright light. 55 Class 3a Lasers This class of intermediate power lasers includes any wavelength. Only hazardous for intrabeam viewing. This class will not cause thermal skin burn or cause fires. Many laser pointers fall into this class 56 28

29 Class 3b Lasers Visible and near-ir lasers are very dangerous to the eye. Pulsed lasers may be included in this class. This class will not cause thermal skin burn or cause fires. Requires registration of the laser, a Laser Safety Officer, Laser Safety Training and written Standard Operating Procedures. 57 Class 4 Lasers These high-powered lasers are the most hazardous of all classes. Even a diffuse reflection can cause injury. Visible and near-ir lasers will cause severe retinal injury and burn the skin. Even diffuse reflections can cause retinal injuries. UV and far-ir lasers of this class can cause injury to the surface of the eye and the skin from the direct beam, diffuse and specular reflections. This class of laser can cause fires. Requires registration of the laser, a Laser Safety Officer, Laser Safety Training and written Standard Operating Procedures

30 Laser Injury Primary sites of damage Eyes Skin Types of laser damage Thermal Acoustic Photochemical 59 Laser Bioeffects-Skin Erythema (inflammation sunburn like reddening) Skin Cancer Accelerated skin aging Increased pigmentation Photosensitive reaction Skin Burn 60 30

31 Photokeratitis Laser Bioeffects-Eye (inflamed cornea) Photochemical Cataract Photochemical retinal injury Thermal retinal injury Retinal burn Aqueous flare Acoustic shock Cataract (permanent clouding of the lens) 61 Warning Labels Only Class 1 lasers require no labels. All other lasers must be labeled at the beam s point of origin. Class 2: Laser Radiation Do Not Stare into Beam. Class 3a: Laser Radiation Do not Stare into Beam or View Directly with Optical Instruments. Class 3b: Laser Radiation Avoid Direct Eye Exposure. Class 4: Laser Radiation Avoid Eye or Skin Exposure to Direct or Scattered Radiation

32 Warning Signs All rooms with class 3b or 4 lasers must have appropriate signs posted at all entrances. Signs must: Have posted safety instructions Indicate laser class Indicate the Type of Laser, emitted wavelength, pulse duration, and maximum output Indicate precautions needed such as PPE requirements for eyewear, etc. 63 DANGER Warning Sign Safety Instructions May Include: Eyewear Required Invisible laser radiation Knock Before Entering Do Not Enter When Light is On Restricted Area 64 32

33 Laser Safety Label the room on the outside Use Laser Safety Eyeware (LSE) More than enough LSA for the wavelength in use On average only 1 in 4 models of laser eyewear were rated acceptable by ECRI 65 Laser Safety Train clinicians in laser safety Ensure physicians are credentialed in the laser and the procedure they are doing Goggles, Spectacles, Wraps 66 33

34 Eye Safety The eye is the organ most sensitive to thermal, mechanical and chemical damage 67 Direct and diffuse reflections can both cause damage Eye Safety Damage is power and time dependent 68 34

35 Skin Safety 69 Fire Safety Lasers can be the ignition source in the fire triangle Take care to minimize gas (O 2 & N 2 O) leaks when lasers are in use Gases pool under drapes and saturate drapes 70 35

36 Laser Safety Use the lowest possible power setting Test fire laser into something safe to ensure the aiming beam and therapeutic beam are in alignment Place laser in standby mode when not in use Activate laser only when tip is in surgeons direct vision Allow only the person using the laser to activate it Place laser in standby mode when removing it from the site 71 Laser Safety Use surgical devices designed to minimize laser reflectance Never clamp laser fibers to drape, clamping can break fibers Insert fiber into endoscope and test before inserting endoscope into patient In lower airway surgery, keep laser tip in view at all times and keep tip clear of end of bronchoscope or trach tube before firing 72 36

37 Laser Safety Use laser backstop to prevent damage distal to surgical site Use laser resistant trach tubes & use dyed saline to fill trach cuff to indicate puncture 73 Laser Safety Keep sponges, gauzes, etc. wet during procedure to minimize chance of ignition If open O 2 delivery, rather than 100% use 30% O 2, then cut off O 2 one minute before activation of laser Use pulse oximeter to measure patient s O 2 saturation, then reduce supplementary O 2 until O 2 sat drops Consider active scavenging of the space beneath the drapes 74 37

38 Laser Safety Organizations which provide guidelines and/or Enforcement: O.S.H.A (Occupational and Safety Health Administration) ANSI (American National Standards Institute) ASLMS (American Society for Laser Medicine and Surgery) AORN (Association of Operating Room Nurses) TJC F.D.A (Food and Drug Administration Center for Medical Devices and Radiological Health) - CDRH And State and Local regulation vary from state to state 75 The Joint Commission Laser Safety HAP EC EP5. The hospital s activities and frequencies for inspecting, testing, and maintaining the following items must be in accordance with manufacturers recommendations: - Medical laser devices - Imaging and radiologic equipment - etc

39 Health Devices Magazine May Evaluations November 2016 January 2017 References OSHA Laser Hazards ( ANSI Z136.1 Laser Safety Standard Laser Institute of America ( Thanks to ECRI for the Information 78 39