laser application in medicine final deka

8/9/2019 Laser Application in Medicine Final Deka

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Laser application in medicine

Lasers are useful in medicine for tworeasons: 1-their amazingly hightemperatures 2-and their incredible precision.

As illustrated below1-Their ultra-high temperatures allow pulsed-energy laser beams (aka excimer lasers) toliterally vaporize organic matter on contact -a self-cauterizing cut that leaves no roughedges and no burnt tissue; the target matteris literally there one instant and gone thenext. One can imagine how useful this mightbe in getting perfect fits between metalprostheses and bone.

2-The incredible precision allows for suchthings as the virtually molecule-by-moleculeremoval of tissue such as that found in abrain or spinal cord to remove tumors orscars from old injuries.

Cancer detection and treatment I-

Photo dynamic therapy


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Besides thermal and mechanical effects, laser canalso induce chemical effects witch are used forphotodynamic therapy (PDT) a photo sensitivedrug is administrated to a patient and then isselectively accumulated in cancerous tissues.

When the tissue is illuminated by a particularwavelength

The drug in the cancerous tissue will emitfluorescence light disclosing the presence of themalignant tissue (fisher et al 1995) in this way defusedeseeded tissue can be detected.

Depending on the drug, another particularwavelength can be used to induce the chemicalprocess that release a toxic component which killsthe malignant cells that contain the drugFor this therapy it's important that the target tissue isilluminated as uniformly as possibleSpecial defusing fiber tips have been developed thatare optimized for the geometry of the target organ.

These are usually spherical or cylindrical.The power density of the tissue surface shouldexceed the threshold level for activationOf the photodynamic drug in the tissue, but the heatinput shouldn't result in hyperthermiaUsually the tissue is exposed to several hundreds ofmilli watts /square cm for several minutes the powershould also be limited to prevent damage to thedefusing tip sense a part of energy is absorbed in thedefusing material.

At this timeThe only PDT approved in most contras is photofrinThis drug is activated near 630 nanometer which iscommonly generated with argon- ion-laser-pumped

dye laser whoever dye lasers pumped with pulsedlaser systems like copper vapor frequency doubled


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Nd: YAG (KTP) and excimer lasers are also attractivebecause of there efficiency (over 30%(

A side effect of photofrin is that the patient is notallowed in bright daylight for several days up toweeks since the drug also sensitizes the skinNew generation PDT drugs with less side effects arealready under clinical investigation

)Fisher et al 1995) they can be exited with the nearIR wavelengths of diode laserSuch lasers are much preferred to the bulk lasercurrently in useClinical trails with PDT drugs are being performed totreat cancers in the skin, lungs, oesophagus, bowelsand bladder and the results are promising

Illustration of laser and treatment ofcancer cells


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The results are promising

Dermatology and aestheticsurgery

Localized superficial skin lesions


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Focusing hand pieces coupled to CO2 lasers are usedfor precise vaporization of skin Lesions like warts andcondilomata.

The hand-pieces have relative short focal length lenses(100-150.(

The spot size on the tissue will be determined by thefocal length and the distance between the lens and thetissueSince the power density is proportional to the square ofthe distance from the focus

The distance is very critical for a controlled tissueeffect.

Typically over a distance of several centimeters thespot size ranges from 0.1-3mmA900 fold variation in power density to keep the powerdensity constant a combinationOf two lenses is used to create a collimated beam

These collimation hand pieces decrease the diameter ofthe beam, while

The spot size is fixed and relatively independent of thedistance to the tissue.

Large superficial skin lesionsWrinkles of the skin can be smoothed by scanning acarbon dioxide laser beam across the skin (Weinstein1994). This application has recently become verypopular in aesthetic surgery within 45 minutes thewhole face of the patient can be treated using thescanning device to remove the epidermis.

Although the superficial skin is peeled ablation.There may Also be a considerable thermal effect


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The heating induces shrinkage of collagen strings in thedermis resulting in a stretching of the wrinkles at thesurface

)its still unknown what will happen to the thermallydamaged collagen in the future(

The scanning system consists of reflectors on a twoaxis system, which irradiate large surface area quicklyand in a controlled manner from a distance using aprocessor-controlled pattern.

This pattern can either be preset from a menu ofoptions or programmed for a specialized treatment. Thetissue is irradiated more evenly, more accurately andfaster than can be achieved manually.

Co2 laser scanning devise


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Depending on the type of carbondioxid laser there aretwo strategies

1-In case of continuous wave co2 lasers ablativetemperatures are obtained instantly, by focusing thebeam to a small spot with a very high power densitythe beam is moved in spiral shape at high speed toobtain a superficial ablation and even surface

For pulsed co2 laser systems the scanners have achoice of pre-set patterns with adjustment for size andoverlap between individual spots in combination withthe pulse energy and repetition of the pattern theablation depth and adjacent thermal effects can becontrolled

The speed of tissue ablation over a large surface isimpressive

Vascular lesions (port wine stains(

Port wine effect are caused by an excess of bloodvessels near the surface of the skin these can bepreferentially destroyed by using a laser wavelengththat is strongly absorbed by the blood.

The leather beam is scanned across the surface in acontrolled mannerVarious scanning systems have been developed for

the selective treatment of these vascular lesions ascanning system (scannall) developed by visiray(Hornsby, Australia) video captures and digits thelesion prior to treatment.A computer calculates the optimal treatment and pathfor scanning of the stain.

The scanning speed is adjusted for the proper energydose per unit area.


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The yellow beam from the copper laser (578 nm) isfocused and scanned over the skin of the patient. Theexposure time per p [position is just sufficient to heatand damage blood vessels.

The minimal thermal relaxation in the surroundingarea to have an optimal preferential effect .a Frenchresearch group has developed the Hexascan (mordonET el 1993.(

The skin is erradiated with consecutive pulses of tensof milliseconds duration .the 1 mm diameter spots fillup the hexagonal shape in such way that eachfollowing spot is fired as far away as possible from theprevious one

Thus heat accumulation can be prevented in one area(apfelperg and smoller 1993(

The total diameter of hexagon can be preset from 1to13 mm the light energy wish is usually from an argonlaser is transported through 400 micrometer fiber to ahand peace in wish the scanner is incorporated

The exit end of the fiber is moved around in the objectplane of a lens.

The image focused as a spot on the surface of thetarget tissue will scan the surface according themotion of the fiber in the object plane the exposuretime of the mechanical shutter is a minimum of 30 millseconds

Similar to the hexascan, a scanner has beendeveloped specially for copper vapor laserapplications the exposure time is controlled both witha mechanical shutter and the scanning speed of thespot Along the surface .the effective exposure time isin the range of 1 to 100 ms .in combination with alarge copper vapor laser system producing over 10

watt of yellow light therapeutic fluences of 10 j /cm2can be obtained a few milliseconds thus


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Preventing collateral thermal damage thiscombination is a good alternative for

The flash lamp pulsed dye laser (Ross et al .1993(

Laser device for treating vascular lesions

By usingNd: YAG

Opthalmology

Inner eye treatment

Optharmology was in the early sixties next todermatology the first field for the applicationof laser.Lasers have been applied successfully sincethen as there unique characteristics enable

treatment of the rear of the eye without any


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surgery for example: diabetic patients oftenhave a growth of blood vessels on the retina.To stop this, laser energy can be focused onthe retina through the transparent eye.Causing partial coagulation of the offendingvessels similarly ruptures of dissectionsOf the retina can be sealed this proceduresare performed on an out clinic bases withinvery short times

Anther simple procedure is the treatmentof secondary glaucoma. due to an adversereaction of the human body on lens implantsa refuse membrane encapsulates theartificial lens blocking clear vision by precisefocusing of the beam from a Q_switched Nd:YAG laser a micro explosion is induced in themembrane, tearing it apart the effect issimilar to the opening of a curtain thepatient walks out of the doctors office within10 minutes with a restored vision

Cornea shaping

By adapting the curvature of cornea the ayecan be corrected for near and far sight by

Up to 4-5 dioptres . Pulses of UV laser lightcan be used to reshape the cornea byselective removal of tissue the 10 ns pulsesof the 193 nm ArF eximer laser light only


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Endoscope device

Ablate a few micrometers of tissue at a time (vansaarloos and constable 1993(The beam is delivered by a mirror system andthe spot cover the whole corneaOne method of ablating the cornea is to the

desired shape is by using a varyingdiaphragm. By a plating the pattern of ringsin the surface of the corneaThe curvatior is adjustedAnther method uses a contact lens with thenegative shape for the adapted lenses thiscontact lens is ablated on the top of thecornea, at some point the beam will

perforateThe thinner parts of the contact lens andstart to ablate the cornea locally as well.Thus the depth of ablated cornea iscontrolled by the local thickness of thecontact lens


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Keyhole. Surgery for superficial

lesionsMucosa defect in mouth, larynx and ear

As shown before the co2 laser is effective forsuperficial applation of small lesions for examplein mucosa this spots can be reached by directingthe laser beam through natural (openings inhuman body) to provide clear vision on area oftreatment the distal end of an articulated arm canbe coupled onto and operating microscope

The beam is aligned along the optical path of theoperating microscope using a small 90 degreedeflector

A joystick is needed to Gide the beam through thefield of view by slightly tilting the angle of thedeflector . The beam is focused on the targettissue using optics with focal length compatible

with the optics of the microscope,,Usually in the range from 200-400nm , again thespot size (power density)will determine theresulting tissue effect .the view through themicroscope enables precise ablation ofmicroscope manipulators are commonly used by


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ENT surgeons (ossoff et al 1994), for example toablate lesions on the larynx, and bygynaecologists, for example , for cervix

ablation..

Endoscopic procedures

To enable exposure of tissue inside the body , thearticulated arm of co2 laser is coupled onto a rigid

endoscope coaxially with the optics for viewing.The laser energy can be used in cavities which arefilled with air as in laparascopic (lanzafam 1990)and thoracoscopic procedures

Sometimes the fluid in cavities like the knee orbladder is temporarily replaced with co2 gas toenable laser exposure in general surgery this

delivery technique is applied to treat smallsuperficial lesions on intestine while in gynecologyendometryces on the outside of the uterus orbladder ablated


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laser application in medicine final deka

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