17 August 2009
The invention: Technique using laser light beams to vaporize the plaque that clogs arteries. The people behind the invention: Albert Einstein (1879-1955), a theoretical American physicist Theodore Harold Maiman (1927- ), inventor of the laser Light, Lasers, and Coronary Arteries Visible light, a type of electromagnetic radiation, is actually a form of energy. The fact that the light beams produced by a light bulb can warm an object demonstrates that this is the case. Light beams are radiated in all directions by a light bulb. In contrast, the device called the “laser” produces light that travels in the form of a “coherent” unidirectional beam. Coherent light beams can be focused on very small areas, generating sufficient heat to melt steel. The term “laser” was invented in 1957 by R. Gordon Gould of Columbia University. It stands for light amplification by stimulated emission of radiation, the means by which laser light beams are made. Many different materials—including solid ruby gemstones, liquid dye solutions, and mixtures of gases—can produce such beams in a process called “lasing.” The different types of lasers yield light beams of different colors that have many uses in science, industry, and medicine. For example, ruby lasers, which were developed in 1960, are widely used in eye surgery. In 1983, a group of physicians in Toulouse, France, used a laser for cardiovascular treatment. They used the laser to vaporize the “atheroma” material that clogs the arteries in the condition called “atherosclerosis.” The technique that they used is known as “laser vaporization surgery.” Laser Operation, Welding, and Surgery Lasers are electronic devices that emit intense beams of light when a process called “stimulated emission” occurs. The principles of laser operation, including stimulated emission, were established by Albert Einstein and other scientists in the first third of the twentieth century. In 1960, Theodore H. Maiman of the Hughes Research Center in Malibu, California, built the first laser, using a ruby crystal to produce a laser beam composed of red light. All lasers are made up of three main components. The first of these, the laser’s “active medium,” is a solid (like Maiman’s ruby crystal), a liquid, or a gas that can be made to lase. The second component is a flash lamp or some other light energy source that puts light into the active medium. The third component is a pair of mirrors that are situated on both sides of the active medium and are designed in such a way that one mirror transmits part of the energy that strikes it, yielding the light beam that leaves the laser. Lasers can produce energy because light is one of many forms of energy that are called, collectively, electromagnetic radiation (among the other forms of electromagnetic radiation are X rays and radio waves). These forms of electromagnetic radiation have different wavelengths; the smaller the wavelength, the higher the energy level. The energy level is measured in units called “quanta.” The emission of light quanta from atoms that are said to be in the “excited state” produces energy, and the absorption of quanta by unexcited atoms— atoms said to be in the “ground state”—excites those atoms. The familiar light bulb spontaneously and haphazardly emits light of many wavelengths from excited atoms. This emission occurs in all directions and at widely varying times. In contrast, the light reflection between the mirrors at the ends of a laser causes all of the many excited atoms present in the active medium simultaneously to emit light waves of the same wavelength. This process is called “stimulated emission.” Stimulated emission ultimately causes a laser to yield a beam of coherent light, which means that the wavelength, emission time, and direction of all the waves in the laser beam are the same. The use of focusing devices makes it possible to convert an emitted laser beam into a point source that can be as small as a few thousandths of an inch in diameter. Such focused beams are very hot, and they can be used for such diverse functions as cutting or welding metal objects and performing delicate surgery. The nature of the active medium used in a laser determines the wavelength of its emitted light beam; this in turn dictates both the energy of the emitted quanta and the appropriate uses for the laser.Maiman’s ruby laser, for example, has been used since the 1960’s in eye surgery to reattach detached retinas. This is done by focusing the laser on the tiny retinal tear that causes a retina to become detached. The very hot, high-intensity light beam then “welds” the retina back into place, bloodlessly, by burning it to produce scar tissue. The burning process has no effect on nearby tissues. Other types of lasers have been used in surgeries on the digestive tract and the uterus since the 1970’s. In 1983, a group of physicians began using lasers to treat cardiovascular disease. The original work, which was carried out by a number of physicians in Toulouse, France, involved the vaporization of atheroma deposits (atherosclerotic plaque) in a human artery. This very exciting event added a new method to medical science’s arsenal of life-saving techniques. Consequences Since their discovery, lasers have been used for many purposes in science and industry. Such uses include the study of the laws of chemistry and physics, photography, communications, and surveying. Lasers have been utilized in surgery since the mid-1960’s, and their use has had a tremendous impact on medicine. The first type of laser surgery to be conducted was the repair of detached retinas via ruby lasers. This technique has become the method of choice for such eye surgery because it takes only minutes to perform rather than the hours required for conventional surgical methods. It is also beneficial because the lasing of the surgical site cauterizes that site, preventing bleeding. In the late 1970’s, the use of other lasers for abdominal cancer surgery and uterine surgery began and flourished. In these forms of surgery, more powerful lasers are used. In the 1980’s, laser vaporization surgery (LVS) began to be used to clear atherosclerotic plaque (atheromas) from clogged arteries. This methodology gives cardiologists a useful new tool. Before LVS was available, surgeons dislodged atheromas by means of “transluminal angioplasty,” which involved pushing small, fluoroscopeguided inflatable balloons through clogged arteries.