Lasers revolutionize medicine – includes advantages and disadvantages, up and coming laser techniques, etc
in Canada today, almost every major hospital uses laser technology to perform certain procedures. As the devices become less expensive and specialists in their use more numerous, lasers are gradually moving into smaller medical centres, taking on newer tasks.
As early as 1917, Albert Einstein had developed the theoretical basis for lasers. The term L-A-S-E-R is an acronym for Light Amplification by Stimulated Emission of Radiation (radiation here meaning light radiation). However, it was only in 1960, following much work by Soviet and U.S. scientists, that an American team of researchers finally overcame the technological hurdles and assembled the first rudimentary but workable laser. Since then, lasers have undergone a rapid advance. Surgeons were quick to recognize the potential for a highly focussed cutting beam. By 1965, the first laser was in use for treating certain eye problems, such as a tom retina. Although the early machines were cumbersome and impractical, by the early 1970s argon lasers were being used experimentally for several medical procedures, including the treatment of diabetic eye problems and removal of small skin growths. Today the instruments are ubiquitous – contributing to areas as diverse as Beatlemania light shows, removing hemorrhoids and eradicating birthmarks. Laser technology has found its way into a broad range of medical specialties: from gynecology, gastroenternology, denistry, dermatology, urology, opthalomology and neurology to ear, nose, and throat surgery, and cancer treatment. Lasers can seal off bleeding blood vessels, kill malignant cells and vaporize away small growths in inaccessible parts of the body, such as the bowel and vocal cords, avoiding the need for surgery. As the machines become cheaper, more manageable and “userfriendly,” small hospitals and clinics are acquiring their own laser centres. Their rapidly expanding repertoire brings significant benefits, in some cases almost replacing conventional therapy. The laser hasn’t yet quite usurped the surgeon’s knife but if present trends continue, the surgical scalpel may ultimately retire to medical museums, along with leech jars and cupping basins. What is a laser? A laser device strengthens or amplifies light, producing a highly directional, very powerful light beam – much like focussing sunlight through a magnifying glass to produce a beam concentrated enough to light a fire. (SEE DIAGRAM). The typical laser, such as the carbon dioxide type, is a tube filled with gas, which is electrically excited” (other lasers may use different gases, liquids or solids as their medium). As an electric current passes through the tube, the gas molecules become charged or excited and emit absorbed or excess energy as photons – tiny “packages of light.” The light is reflected back and forth by mirrors at either end of the tube, a process that amplifies the energy, producing an intense light beam of a single wavelength or colour. The beam comes out through a partially silvered mirror at one end of the device as an ultra fine, very strong light beam that can deliver extreme heat. In producing light beans with different properties, laser technology takes advantage of the special characteristics of a whole range of gases, solids and liquids, some of them exotic elements – including argon, krypton, neodyminum, titanium and holmium. Depending on the substance used, the laser beam has a longer or shorter wavelength. The wavelength and pulse time determine the laser’s properties – its colour and what it can do. For instance, carbon dioxide lasers operate in the infra-red spectrum, invisible to the human eye; argon lasers have a visible bluish green hue; krypton lasers are reddish. (The colours of lasers are utilized in light shows.) Most important to medical specialists, their different wavelengths have diverse effects on human tissue. Each laser has its own unique properties and is used for different procedures: photoablation (vaporizing/ melting tissue), photodisruption (breaking chemical bonds) or photocoagulation (sealing, shutting). Depending on the type of laser, its beam can cut tissue like a sharp razor, coagulate it like thickening egg white, shrink/shrivel it or vaporize it away. For example, the beam of a carbon dioxide laser cuts human flesh better than the finest surgical scalpel, surpassing even diamond knives, coagulating blood vessels as it goes so that they don’t bleed – very useful for intricate surgery. Different lasers for different medical uses Although new lasers are continually being developed, those most prevalent in medicine today are: the carbon dioxide (CO,) laser, the neodymium-yttrium-aluminium-garnet solid state laser (Nd:YAG) and the argon laser. Lasers recently introduced for medical uses include the excimer laser and the tunable dye laser.
Carbon dioxide CO2) lasers: The infra-red beam of the carbon dioxide laser cuts tissue by vaporizing it. “Vaporizing” is just what it sounds like – tissues are burnt away. Cells absorb laser light to the boiling point of water and then explode in a puff of steam and cellular detritus called a “laser plume.” In the hands of a skillful operator, the focussed beam of the CO, laser performs better than the finest surgical knife, avoiding the mechanical damage of conventional surgery, reducing postoperative bleeding, scarring and swelling. More precise than a knife or scalpel, lasers allow surgeons to cut out exactly what is required with minimal harm to surrounding tissues. Furthermore, since the heat of the CO, laser seals shut the cut surfaces of tiny blood vessels, it makes laser surgery almost bloodless in some cases. However, while a knife cuts deeply and swiftly, a carbon dioxide laser proceeds layer by layer, finding maximum effectiveness in delicate operations and such procedures as removing genital warts or excising small skin cysts. One disadvantage of the CO.sub.2 laser is its relative inflexibility and superficial range. It cannot reach far into the body for deep internal procedures, nor can it be attached to a fibreoptic viewing tube or endoscope. However, with the aid of a thin metal tube, the CO, beam can be guided to specific sites much like moving water through a hose – for broader use, for instance in throat surgery. Another limitation is the need for elaborate safety precautions. The eyes must be protected. And the smoke, spray and stench from carbon dioxide surgery, which can be considerable, especially in gynecological procedures, means that operating staff must wear masks to minimize throat irritation and reduce the risk of contamination from breathing in the plume. * Nd. YAG lasers: The neodymium-yttrium-aluminizim-garnet laser (Nd: YAG) operates in the near infra-red range. Not being visible to the eye, a low-power pilot (laser) light is used to guide the Nd: YAG beam. Having a shorter wavelength than the CO, laser, the YAG beam can penetrate deeper into tissues – as deep as two to six mm. Another advantage of the ND:YAG is that unlike the more cumbersome CO, laser, its light can be transmitted through long, flexible fibreoptic cables enabling it to reach inaccessible parts of the body. The ND:YAG laser is now widely used for deep internal procedures, for instance to coagulate a bleeding stomach ulcer or to shrink bulky colorectal growths in the bowel, also to treat bladder disorders and brain tumours. According to wave duration (power), the ND:YAG does different things. At low power it destroys cells by denaturing protein (disrupting molecular structure), rather as egg white solidifies and turns opaque when heated, so that the cells die and slough off. At higher power, it vaporizes tissue and because it scatters heat widely is ideal for “de-bulking” or shrinking cancerous growths (shrivelling them up, much like a grape loses water to become a raisin).
Argon lasers: The blue-green beam of an argon laser is selectively absorbed by tissues of certain colours – only by dark tissues such as blood (containing the red pigment, hemoglobin) and brown or black tissues (such as skin containing the pigment, melanin). Since the argon laser’s light is absorbed mainly by red and brown colours and only to a depth of about 0.5-2 mm, it’s ideal for treating skin and eye problems. Its affinity for red-coloured tissues makes it particularly useful for removing “port wine” birthmarks. Argon lasers are now widely used for treating certain eye disorders. In fact, ophthalmologists first employed argon lasers to treat diabetic retinopathy (an abnormal growth of blood vessels on the retina – at the back of the eye – which may cause blindness). Argon lasers are also used to treat detached retinas, sealing back the loosened part. * The Q-switched ruby laser. The first laser ever devised, it’s now being explored for new uses such as removal of birthmarks.
Newer lasers: Innovative laser technologies are continually being explored – especially new cutting tips, probes and delivery systems. Novel medical lasers include: * The cold” ultraviolet excimer laser, using halogen gases such as xenon chloride or or krypton fluoride, produces an extremely precise and superbly clean cut not by heat but by breaking chemical bonds. Delivered as a series of rapid pulses, it gives greater control over some procedures than other lasers and is opening up new avenues of research, for example in reshaping the cornea to change the eye’s refractive state. restoring focussing ability. Perhaps in future this technique will enable some who need glasses to do without them. Argon lasers are also being investigated in cardiology, for instance to vaporize away arterial heart blockages. * Pulsed or tunable dye lasers, based on organic dyes, tunable to wavelengths in the 550-630 nm region, surpass argon lasers for treating specific skin problems – especially for superficial vascular problems on the face such as “spidery” blood vessels and to remove certain birthmarks without scarring. * Soft or “cool” low power lasers, such as the helium neon and the gallium-aluminium-arsenide types, operate at very low wattages and diode tubeless devices (in the 810 nm wavelength band) may be the types of the future. At present, soft lasers are mainly “coagulators” that supposedly work by biostimulation. They’re being promoted to speed wound healing and to relieve muscle pain, soften wrinkles, alleviate arthritic aches and even to cure “bowed tendons” in horses. Widely used in Europe although not here yet), especially for arthritic pain, most claims for their healing capacity remain unsubstantiated. The ability of soft lasers to help people quit smoking also remains unproven. In the U.S., soft lasers are even advertised as baldness remedies and for face toning – statements best regarded with skepticism. Although low wattage laser beams are deemed harmless and heat human tissue no more than a degree or two, they probably only work (if at all) as placebos. Nonetheless, some clinical trials suggest that cold laser therapy may offer some relief for certain painful conditions, such as rheumatoid arthritis and muscular strain and may speed up the very early stages of wound healing. To date, overall evidence of their usefulness remains unsatisfactory. Laser applications: some highlights
For treating certain eye disorders. Since ophthalmologists first adopted lasers to treat retinal eye disorders in the mid- 1960s, their use has been extended to treat many eye problems, enabling surgeons to work with local anesthesia. Argon lasers are widely used for treating diabetic retinopathy – a major cause of blindness (due to an abnormal collection of retinal blood vessels which become leaky). The argon laser beam penetrates the clear watery cornea without harming it and photocoagulates the bleeding vessels at the back of the eye, halting disease progression, although it can’t always restore any vision already lost. Lasers are also invaluable for spot-welding tiny tears/holes that may lead to retinal detachment. Similarly, argon lasers are sometimes used for age-related macular degeneration (a major cause of vision loss in those over age 60). Both argon and Nd: YAG lasers can zap tiny holes in the eye’s iris to alleviate the fluid buildup and pressure of glaucoma and to promote the flow of fluid away from the eye in open angle glaucoma. Contrary to popular misconception, lasers are not used in cataract surgery, although the ND:YAG is sometimes employed after cataract surgery, to clear a cloudy layer behind the lens implant. (For more on cataracts, see Health News April 1987). * For gastrointestinal/digestive tract problems. Fibreoptic delivery systems have revolutionized the use of lasers in stomach and intestinal problems. The attachment of argon and ND:YAG lasers to long fibreoptic cables enables doctors to see and reach otherwise inaccessible parts of the body, which formerly required major surgery. In diagnosing and treating digestive system problems, a surgeon can watch the laser’s progress through the endoscope as it travels along the digestive tract on a video screen and accurately coagulate or vaporize away small tumours, ulcers or other lesions deep within the body. Endoscopic laser therapy is now often used to shrink large cancerous colorectal tumours that obstruct bowel function, making patients more comfortable. Laser therapy, often done under local anesthesia, produces less scaning than electrocautery (done with electrical heating probes) and can be repeated if necessary. The tunable dye laser also serves as a palliative rather than curative tool for rapidly shrinking bulky growths to improve the quality of life in the late stages of cancer. Laser treatment can shrink inoperable esophageal tumours which cause dysphagia inability to swallow). Lasers also provide an alternative treatment for hemorrhoids, more popular in the U.S. than here since there’s some controversy over its effectiveness compared to conventional treatment.
For removal of gynecological growths. Both CO, and YAG lasers are now widely used to eradicate lesions of the vulva, vagina and cervix (opening of the uterus/womb) and for vaporizing away genital warts. Done easily and rapidly, on an out-patient basis, laser vaporization of noncancerous cervical growths leaves the cervix in considerably better shape than conventional therapy – with less scaning, stenosis (constriction, narrowing) and postoperative pain or discharge. Lasers are also used to treat some forms of excess menstrual bleeding and for mild to moderate endometriosis (spread of the uterine lining outside the womb) vaporizing away the endometriomas or adhesions. Usually done by laparoscopy (via a viewing tube inserted through a tiny cut in the navel), it reduces the need for a more extensive incision. CO, lasers can clear obstructed fallopian tubes and ovaries to overcome some infertility problems and also help to vaporize cysts and small tumours, with minimal damage to nearby tissues. For ectopic (tubal) pregnancies, lasers prove invaluable in reducing the massive blood loss that frequently accompanies the surgical management of this emergency.
For ear, nose and throat surgery. Both CO 2and Nd:YAG lasers are useful because they produce less airway swelling than surgical cutting – a serious complication in conventional operations. CO 2 lasers, now adapted for a longer reach, allow deeper procedures to be undertaken with less pain, sometimes reducing the need for a tracheotomy (cutting of the windpipe to relieve obstruction of breathing). Vocal cord nodules, polyps, cysts and small lesions of the tongue and nose may also lend themselves to laser removal.
For mouth and tooth problems. Laser diagnosis and treatment of tooth disease is under investigation but highly controversial. For example, split-second laser bursts can get rid of tiny tooth irregularities that harbour decayforming plaque. Lasers can also sterilize infected root canals and remove pre-malignant lesions from the cheeks, tongue and floor of the mouth. But it may take years before their use becomes accepted practice in dental offices.
For brain and nerve disorders. CO, lasers have a unique place because brain operations can be done with minimal damage to neighbouring areas. The less the tearing and tugging of brain tissue the better the recovery and the fewer post-operative complications.
For skin problems such as removal of birthmarks, tattoos and other blemishes. Laser treatment now offers startling improvement to people with certain birthmarks who formally had to “accept and tolerate” or cover the blemish with make-up. One valuable niche for lasers in treating skin disorders is for removing undesirable stains, particularly port wine birthmarks, such as the one on Soviet leader Mikhail Gorbachev’s forehead – one of the most effective treatments found to date for obliterating these skin marks. The argon laser beam passes through the skin’s surface to coagulate and seal blood vessels underneath, stifling the blood supply, bleaching or eradicating the red patch. While removal of birthmarks with argon lasers gives reasonable results in adults, in children it may replace a stain with a disfiguring scar – a drawback overcome by using pulsed tunable dye lasers which can remove port wine stains without scaning. Toronto’s Hospital for Sick Children now has a tunable dye laser for eradicating unwanted birthmarks. The removal of tattoos by laser technology is being tried in the U.S. and Britain, results so far less than perfect. Laser treatment may remove the tattoo but leaves a scar. The Q-switched ruby laser shows greater promise in tattoo removal but isn’t yet used for this purpose in Canada. More on tattoos and birthmarks in the next issue of Health News.) On the horizon and around the corner
Up and comming laser techniques include: * Photodynamic laser therapy (PDT)for cancer treatment and diagnosis: Canada is a leader in the burgeoning field of photodynamic therapy or laser photoradiation to destroy malignant tissue. The technique is now undergoing clinical trials in Toronto and across Canada, particularly for bladder and brain cancer. In destroying cancerous cells without harming healthy tissue, photoradiation employs special lightactivate drugs that are injected and selectively taken up or concentrated by malignant cells. When laser light shines into the tumour it switches on the drug, causing it to release a singlet-oxygen -toxic product that makes the growth shrivel up and slough off. Health and Welfare Canada is currently considering the approval of photoporphyrin, the light-sensitive drug manufactured by a Vancouver company, for clinical laser therapy in some types of lung cancer. The hope is that it may provide ail alternative to more invasive therapies, reducing tile need for surgery and radiation. Laser therapy can be used alongside coventional treatment. PDT is also useful in identifying cancer cells and detecting early signs of malignacy, especially esophageal and lung cancer. One know disadvantage to PDT is that the ingested drug produces temporary photosensitivity to UV light, with risks of a severe sunburn if the patient goes into sunlight for a few weeks afterwards. Otherwise it is non-toxic. * Laser lithotripsy for gallbladder and kidneystones: The University of Toronto’s Mount Sinai Hospital recently became the first Canadian centre to acquire a flashlamp pumped tunable dye laser to fragment large gall and kidney stones. Brief flashes of laser ligiht shatter the stones so that the fragments can easily be extracted by a “basket” or pass out in the urine. eliminating the need for major surgery.
* Laser Treatment for arterial diseases: Excimer lasers may in future prove useful for certain heart conditions for example to vaporize away blockages in the coronary arteries. Research in laser surgery is ongoing at the Ottawa Heart Institue, where in 1988 the first completely blocked coronary artery wits cleared during surgery with an excimer laser. Evidence to date suggests that re-narrowing of the heart arteries is less frequent after laser treatment than following balloon angioplasty or bypass surgery. But so fir, lasers have been most useful in removing atheromatous plaque(blockages) from the walls of large vessels – such as le, arteries. * Eye sculpturing to cure shortsightedness: Techniques using an ultraviolet cold excimer laser to photoblate and re-shape the eye’s cornea – by microscopically shaving its surface – are being extensively tried in Europe and the U.S. for correcting myopia or short sightedness. Results so far are promising although not entirely predictable, but the still-experimental method may some day make eyeglasses for short-sightedness obsolete. J Advantages of lasers over more conventional techniques Advantagaes of lasers over more conventional techniques * No need for direct contact or “touch ” – The operator often does not touch the patient during an entire laser treatment. For example, endoscopic laser work, done by “remote control” down a viewing instrument, hardly seems like surgery at all. For instance, when curing a stomach problem by laser treatment, the surgeon simply guides the viewing tube down the patient’s throat into the stomach and operates from outside. The absence of an incision (no cutting) minimizes the risk of infection. * Precision – Laser procedures are very precise, enabling removal or cautery (burning) of the exact amount of tissue required, with greater control and less mechanical disturbance than surgery and consequently better results – less post-operative scarring, pain and swelling, therefore swifter recovery and reduced hospital stays. * Less blood loss – The laser beam often seals shut tiny blood vessels during surgery resulting in a “dry” surgical field with less blood loss, of particular value to hemophiliacs who have an inherited bleeding disorder. in general, laser surgery requires fewer blood transfusions, lessening the risks of blood-borne diseases. * Less invasive to the body- An important benefit, laser surgery can often be performed on an out-patient basis, under local anesthesia, allowing speedier recovery than for operations done under general anesthesia. Some surgical procedures that would in the past have been major bowel or gynecologic operations have become no more traumatic or time-consuming than a trip to the dentist. And laser therapy can often be repeated with no risk of scarring. * Often less painful – The reduced pain or discomfort frequently permits laser procedures to be done with no or little anesthesia, on an out-patient basis. * Easier access to awkward sites – The destruction of deep internal tumours with minimal disturbance of surrounding areas, for instance in brain surgery, is a great advance. * Possibly decreased risk of malignant metastases (cancer spread) – The laser beam may seal off lymph ducts preventing the spread of malignant metastases, but it is not yet proven that laser surgery confers less risk of secondary cancers than cold knife surgery. Disadvantages of lasers * Risk of contamination to the operating crew Laser vaporization might endanger the surgical staff, because the plume of a CO, laser, released as a whiff of smoke and cellular debris, may contain viable tumour cells, viruses and other potentially harmful substances. To lessen the danger, laser teams employ smoke suctioning devices and wear face masks. * Heat damage – The intense heat produced by some lasers can threaten both patient and operating crew. A laser burn may be serious, especially to the eyes. There have been rare reports of endotracheal tubes led into the trachea or windpipe during laser surgery) catching fire, producing serious burns. In addition, the laser itself poses a fire hazard and must be housed in a well fireproofed room. * Eye protection a must – Mandatory because laser light, especially reflected from gleaming metal surfaces, can seriously damage the eyes. * Risk of inhaling toxic fumes from gases used in excimer lasers – Necessitates an efficient exhaust system. 9 Need for extensive safety precautions – While most large hospitals have a safety committee to ensure that lasers are only used by properly accredited, experienced personnel, there are no legal requirements and some experts worry that some hospitals may not adequately follow safety regulations.
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