X rays are electromagnetic radiation that differentially penetrates structures within the body and creates images of these structures on photographic film or a fluorescent screen. These images are called diagnostic x rays.
Diagnostic x rays are useful in detecting abnormalities within the body. They are a painless, non-invasive way to help diagnose problems such as broken bones, tumors, dental decay, and the presence of foreign bodies.
X rays are a form of radiation similar to light rays, except that they are more energetic than light rays and are invisible to the human eye. They are created when an electric current is passed through a vacuum tube. X rays were accidentally discovered in 1895 by German physicist Wilhem Roentgen (1845-1923), who was later awarded the first Nobel Prize in physics for his discovery. Roentgen was also a photographer and almost immediately realized that the shadows created when x rays passed through the body could be permanently recorded on photographic plates. His first x-ray picture was of his wife's hand. Within a few years, x rays became a valued diagnostic tool of physicians world-wide.
How x rays work
X rays pass easily through air and soft tissue of the body. When they encounter more dense material, such as a tumor, bone, or a metal fragment, they are stopped. Diagnostic x rays are performed by positioning the part of the body to be examined between a focused beam of x rays and a plate containing film. This process is painless. The greater the density of the material that the x rays pass through, the more rays are absorbed. Thus bone absorbs more x rays than muscle or fat, and tumors may absorb more x rays than surrounding tissue. The x rays that pass through the body strike the photographic plate and interact with silver molecules on the surface of the film.
Once the film plates have been processed, dense material such as bone shows up as white, while softer tissue shows up as shades of gray, and airspaces look black. A radiologist, who is a physician trained to interpret diagnostic x rays, examines the pictures and reports to the doctor who ordered the tests. Plain film x rays normally take only a few minutes to perform and can be done in a hospital, radiological center, clinic, doctor's or dentist's office, or at bedside with a portable x-ray machine.
Special types of x-ray procedures
Mammograms are fixed plate x rays that are designed to locate tumors within the breasts. Dental x rays are designed to locate decay within the tooth. Sometimes a liquid called contrast material (for example, barium) is used to help outline internal organs such as the intestines. The contrast material absorbs x rays, helping to make soft tissue more easily visible on the x-ray films. Contrast material is commonly used in making x rays of the digestive system. The contrast liquid can be swallowed or injected, depending on the part of the body being x rayed. This may cause some minor discomfort.
Fluoroscopy is a special x-ray technique that produces real-time images on a television monitor. With fluoroscopy, contrast material is injected into a blood vessel. The physician can then watch the real-time movement of the contrast material to determine if there are blockages in circulation. Fluoroscopy is also used to help guide catheters into place in the heart during cardiac catheterization or to guide an endoscope during endoscopic surgery.
Computed tomography or CT scan works on the same principles as fixed plate x rays, only with a CT scan, an x ray tube rotates around the individual, taking hundreds of images that are then compiled by a computer to produce a two-dimensional cross section of the body. Although many images are taken to produce a CT scan, the total dose of radiation the individual is exposed to is low. Other common imaging techniques such as magnetic resonance imaging (MRI) and ultrasound do not use x rays.
How x rays are performed
Fixed plate x rays are extremely common diagnostic tests. A trained x-ray technologist takes the x ray. The individual is first asked to remove clothing and jewelry and to wear a hospital gown. The x ray technologist positions the patient appropriately, so that the part of the body to be x rayed will be between the x-ray beam and the film plate. Usually the individual either lies on an adjustable table or stands. Parts of the body that are especially sensitive to damage by x rays (for example, the reproductive organs, the thyroid) are shielded with a lead apron. Lead is very dense and effectively protects the body by stopping all x rays.
It is essential to remain motionless during the x ray, since movement causes the resulting picture to be blurry. Sometimes patients are asked to hold their breath briefly during the procedure. Children who are not old enough follow directions or who cannot stay still may need to be restrained or given medication to sedate them in order to keep them still enough to obtain useful results. Sometimes parents can stay with children during an x ray, unless the mother is pregnant, in which case she must protect the fetus from x-ray exposure.
If a contrast material is to be used, the individual will be given special instructions to prepare for the procedure and may be asked to remain afterwards until recovery is complete. (See Preparation and Aftercare below.)
Although unnecessary exposure to radiation should be avoided, the low levels of radiation one is exposed to during an x ray does not cause harm with a few exceptions. Pregnant women should not have x rays unless in emergencies the benefits highly outweigh the risks. Exposure of the fetus to x rays, especially during early pregnancy can increase the risk of the child later developing leukemia. Body parts not being x rayed should be shielded with a lead apron, especially the testes, ovaries, and thyroid.
No special preparation is needed for fixed plate x rays unless contrast material is used. When x rays are scheduled that involve the use of contrast material, the physician will give specific instructions for preparation. For example, in a lower GI series, the individual may have to fast and use special laxatives to cleanse the bowel before swallowing the contrast material. Parents can prepare children for x rays be explaining what will happen and that these tests are short and painless.
Little aftercare is needed following an x ray. In complicated x rays where contrast material is injected into a blood vessel, the individual may need to remain under medical care for a short while to assure that there is no allergic reaction to the contrast material and recovery is complete.
Contrast agent —Also called a contrast medium, this is usually a barium or iodine dye that is injected into the area under investigation. The dye makes the interior body parts more visible on an x-ray film.
Endoscope —A medical instrument that can be passed into an area of the body (the bladder or intestine, for example) to allow visual examination of that area. The endoscope usually has a fiberoptic camera that allows a greatly magnified image to be shown on a television screen viewed by the operator. Many endoscopes also allow the operator to retrieve a small sample (biopsy) of the area being examined, to more closely view the tissue under a microscope.
Low dose exposure to x rays creates minimal cell damage and minimal risk when x rays are performed in an accredited facility. There is an increased risk that a developing fetus will develop leukemia during childhood if exposed to x-ray radiation; pregnant or potentially pregnant women should avoid x rays. There is also a slight risk of an allergic reaction to the contrast material or dye used in certain x rays.
Some parents are concerned about health consequences of their child's exposure to x-ray radiation. However, doses of radiation received in most x rays are quite similar to the environmental (background) radiation one is exposed to simply by living on Earth. Although unnecessary x rays should be avoided, in most cases, the benefits greatly outweigh the potentially small increased risk of exposure.
See also Computed tomography.
Faculty Members at the Yale University School of Medicine and G.S. Sharpe Communications, Inc. "Chapter 3 Diagnostic Imaging." The Patient's Guide to Medical Tests, 2nd ed. New York: Houghton Mifflin, 2002.
Cooper, Phyllis G. "X-Rays During Pregnancy." Clinical Reference Systems Annual, 2002 p3574.
American College of radiology 1891 Preston White Drive, Reston, Virginia 20191-4397. Telephone (800) 227-5463. <www/acr.org/flash.html>
Cameron, John R. "Understanding X-rays." eMedicine.com Consumer Health 2003 [cited 22 September 2004]. <www.emedicinehealth.com/fulltext/12071.htm>
Harvard Medical Schools Consumer Health Education. "X-Rays." InteliHealth Procedures and Treatments 3 June 2003 (cited 22 September 2004) <www.intelihealth.com>
Tish Davidson, A.M.
The X-rays were also called ‘skiagrams’ (coined by Rowland) or ‘shadows’ at that time. When Röntgen observed the ‘new light’ he called it an X-ray, because it had been unknown; the name has persisted, although the deservedly eponymous alternative, Röntgen ray, is also used.
During the first two decades, the use of X-rays spread widely, mainly to define fractures and foreign bodies such as bullets — first in the Boer War and later in World World War I. Screening, or fluoroscopy (allowing the doctor to view the patient under X-ray, without taking a ‘still’ photograph), was a frequent alternative to radiographs. At that time electricity supplies were unstable and, before examining the patient, radiologists, or their technical assistants, radiographers, would place their own hands in the X-ray beam as a test for optimum exposure. Little was appreciated of the dangers of X-rays and protection was unknown, but the hazards all too soon became apparent. Frequent exposure led to radiation burns, loss of fingers, and fatal skin cancers. A Martyr's Memorial was erected in Hamburg in 1936 by the German Röntgen Society, inscribed with the names of 169 X-ray and radium martyrs from 15 countries who by then had died; the highest tolls recorded were 14 British, 20 German, 39 American, and 40 French. Twenty-eight more British names were later added. It was not until the 1920s that any protective requirements became obligatory, although some steps had been taken earlier — notably, the London Hospital in 1908–9 was among the first to provide protection for operators.
While the specialty of radiology has undergone incredible changes and now incorporates a wide range of imaging techniques, X-rays remain the cornerstone, accounting for a least 60–80% of all diagnostic imaging examinations. In all such systems X-rays are produced in a glass vacuum tube by electrons striking a tungsten target. The resulting beam of X-rays, invisible to the eye, directed at the part being examined, passes through the patient's body. Various structures absorb the X-ray photons differentially: bones more than soft tissues; other organs and tissues such as muscle producing shadows of varying intensity. The image is recorded by a detection device, either a fluorescent screen (screening) or photographic film (radiography). However, using X-rays alone it is not possible to distinguish between soft tissues of the same density, and to do this various liquid or gaseous contrast media are used. The American physiologist Walter Cannon (1871–1945) was a pioneer in this field who devised this way, now in routine diagnostic use, of examining the internal workings of the body without recourse to surgical interference. He utilized the newly discovered X-rays to examine the passage of food which had been mixed with a radio-opaque substance through the gut of humans and experimental animals. He was initially interested in the mechanisms of swallowing, but subsequently, using a range of foods, he analysed the mechanical properties of every region of the gut. Pictures of the ‘J’ shape of the stomach and pylorus during gastric emptying were originally traced onto lavatory paper held over the Röntgen screen: they are still the classic illustrations used in many textbooks.
Barium is used by mouth to outline the stomach (barium meal), or per rectum to outline the large bowel (barium enema). Water-soluble contrast media can be injected into blood vessels or the chambers of the heart to produce an angiogram, or to be excreted by the kidneys, giving an image of the urinary tract: an intravenous urogram. With such techniques it is possible to investigate virtually any part of the body by X-ray, to give information not only about structure but also about function. These contrast studies, along with X-rays of bones and of the chest, form a very large component of the practice of radiology.
X-ray tomography is a further technique used to define deep internal structures more clearly. In ‘linear tomography’ the X-ray tube, emitting a beam of X-rays, moves in a straight line while the X-ray film moves in the opposite direction. In this way most structures are blurred by the movement but the image is focussed at a particular plane, so giving greatly improved definition. More complicated variations include circular and multidirectional tomography, producing even sharper images. This type of tomography was widely used in the past to define bones, kidneys, or the inner ear, but has now largely been supplanted by computed tomography (see imaging techniques).
With so many patients having X-ray examinations, protection from the dangers of radiation has become of paramount importance. X-ray tubes are encased in lead shields and fully protected and equipment is regularly calibrated. Staff are required to wear lead aprons and to remain behind protective screens during exposures, and their radiation dose is monitored by a device contained in a ‘badge’ which they wear all the time. Likewise patients must be properly supervised and protected. Gonad protection is essential especially in women of child-bearing age. There must be ‘a clear-cut clinical indication’ before any X-ray is requested so that unnecessary tests are avoided. All X-ray examinations must be directed by a properly trained physician, almost always a radiologist. If recognized practice is followed, the dangers from diagnostic X-rays are negligible.
The damaging properties of X-rays have been put to positive use in radiotherapy; already in the early 1900s this was established for the treatment of skin diseases and cancers. Despite the advent of radioisotopes in radiotherapy, X-rays continue to be used for this purpose in appropriate cases.
J. K. Davidson
Mould, R. F. (1980). A history of X-rays and radium. IPC Business Press Ltd, Sutton, Surrey.
See also imaging techniques; radiation, ionizing; radiology.
X rays are a form of electromagnetic radiation with wavelengths that range from about 10−7 to about 10−15 meter. No sharp boundary exists between X rays and ultraviolet radiation on the longer wavelength side of this range. Similarly, on the shorter wavelength side, X rays blend into that portion of the electromagnetic spectrum called gamma rays, which have even shorter wavelengths.
X rays have wavelengths much shorter than visible light. (Wave lengths of visible light range from about 3.5 × 10−9 meter to 7.5 × 10−9 meter.) They also behave quite differently. They are invisible, are able to penetrate substantial thicknesses of matter, and can ionize matter (meaning that electrons that normally occur in an atom are stripped away from that atom). Since their discovery in 1895, X rays have become an extremely important tool in the physical and biological sciences and the fields of medicine and engineering.
X rays were discovered in 1895 by German physicist William Roentgen (1845–1923) quite by accident. Roentgen was studying the conduction of electricity through gases at low pressure when he observed that a fluorescent screen a few meters from his experiment suddenly started to glow. Roentgen concluded that the glow was caused by certain unknown rays that were given off in his experiment. Because of its unknown character, he called this radiation X rays.
Roentgen discovered that these rays were quite penetrating. They passed easily through paper, wood, and human flesh. He was actually able to insert his hand between the source and the screen and see on the screen the faint shadow of the bones in his hand. He concluded that more dense materials such as bone absorbed more X rays than less dense material such as human flesh. He soon found that photographic plates were sensitive to X rays and was able to make the first crude X-ray photographs.
Words to Know
Anode: Also known as target electrode; the positively charged electrode in an X-ray tube.
Cathode: The negatively charged electrode in an X-ray tube.
Computerized axial tomography (CAT scan): An X-ray technique in which a three-dimensional image of a body part is put together by computer using a series of X-ray pictures taken from different angles along a straight line.
Electrode: A material that will conduct an electrical current, usually a metal, used to carry electrons into or out of an electrochemical cell.
Hard X rays: X rays with high penetrating power.
Nondestructive testing: A method of analysis that does not require the destruction of the material being tested.
Soft X rays: X rays with low penetrating power.
Synchrotron radiation: Electromagnetic radiation from certain kinds of particle accelerators that can range from the visible region to the X-ray region.
X-ray tube: A tube from which air has been removed that is used for the production of X rays.
Production of X rays
The method by which X rays were produced in Roentgen's first experiments is basically the one still used today. As shown in the accompanying X-ray tube drawing, an X-ray tube consists of a glass tube from which air has been removed. The tube contains two electrodes, a negatively charged electrode called the cathode and a positively charged target called the anode. The two electrodes are attached to a source of direct (DC) current. When the current is turned on, electrons are ejected from the cathode. They travel through the glass tube and strike a target. The energy released when the electrons hit the target is emitted in the form of X rays. The wavelength of the X rays produced is determined by the metal used for the target and the energy of the electrons released from the cathode. X rays with higher frequencies and, therefore, higher penetrating power are known as hard X rays. Those with lower frequencies and lower penetrating power are known as soft X rays.
Applications of X rays
Medical. The earliest uses of X rays were based on the discoveries made by Roentgen, namely their ability to distinguish bone and teeth from flesh in X-ray photographs. When an X-ray beam is focused on a person's hand or jaw, for example, the beam passes through flesh rather easily but is absorbed by bones or teeth. The picture produced in this case consists of light areas that represent bone and teeth and dark areas that represent flesh. Some applications of this principle in medicine are the diagnosis of broken bones and torn ligaments, the detection of breast cancer in women, or the discovery of cavities and impacted wisdom teeth.
X rays can be produced with energies sufficient to ionize the atoms that make up human tissue. Thus, X rays can be used to kill cells. This is just what is done in some types of cancer therapy. X-radiation is directed against cancer cells in the hope of destroying them while doing minimal damage to nearby normal cells. Unfortunately, too much exposure of normal cells to X rays can cause the development of cancer. For this reason, great care is taken by physicians and dentists when taking X rays of any type to be sure that the exposure to the rest of the patient's body is kept at an absolute minimum.
A relatively new technique for using X rays in the field of medicine is called computerized axial tomography, producing what are called CAT scans. A CAT scan produces a cross-sectional picture of a part of the body that is much sharper than a normal X ray. Normal X rays are taken through the body, producing a picture that may show organs and body parts super-imposed
on one another. In contrast, in making a CAT scan, a narrow beam of X rays is sent through the region of interest from many different angles. A computer is then used to reconstruct the cross-sectional picture of that region.
Nondestructive testing. The term nondestructive testing refers to methods that can be used to study the structure of a material without destroying the material itself. For example, one could find out what elements are present in a piece of metal alloy by dissolving the alloy in acid and conducting chemical tests. But this process of testing obviously destroys the alloy being tested.
X rays can be used to study the structure of a material without actually destroying it. One approach is based on the usual method of producing X rays. A sample of unknown material is used as the target in an X-ray machine and bombarded with high energy electrons. The X-ray pattern produced by the sample can be compared with the X-ray patterns for all known elements. Based on this comparison, the elements present in the unknown sample can be identified. A typical application of this technique is the analysis of hair or blood samples or some other material being used as evidence in a criminal investigation.
X rays are used for nondestructive testing in business and industry in many other ways. For example, X-ray pictures of whole engines or engine parts can be taken to look for defects without having to take an engine apart. Similarly, sections of oil and natural gas pipelines can be examined for cracks or defective welds. Airlines also use X-ray detectors to check the baggage of passengers for guns or other illegal objects.
Synchrotron radiation. In recent years an interesting new source of X rays has been developed called synchrotron radiation. Synchrotron radiation is often produced by particle accelerators (atom-smashers). A particle accelerator is a machine used to accelerate charged particles, such as electrons and protons, to very high speeds. As these particles travel in a circle around a particle accelerator, they may give off energy in the form of X rays. These X rays are what make up synchrotron radiation.
One of the more important commercial applications of synchrotron radiation is in the field of X-ray lithography. X-ray lithography is a technique used in the electronics industry for the manufacture of high density integrated circuits. (A circuit is a complete path of electric current, including the source of electric energy.) The size of the circuit elements is limited by the wavelength of the light used in them. The shorter the wavelength the smaller the circuit elements. If X rays are used instead of light, the circuits can be made much smaller, thereby permitting the manufacture of smaller electronic devices such as computers.
[See also Electromagnetic spectrum; Particle accelerators ]
X rays are a type of radiation used in imaging andtherapy that uses short wavelength energy beams capable of penetrating most substances except heavy metals.
Diagnostic x rays are some of the most powerful medical imaging tools available. Other imaging techniques that do not use x rays include magnetic resonance imaging (MRI), ultrasonography , and radionucleotide imaging. Based on the symptoms presented by the patient, the physician can request specific x rays (such as chest x rays) that help diagnose many types of cancers, including sarcomas , lymphomas, and lung cancers. X rays allow the physician to visualize certain internal body conditions with little or no invasive procedures. Conditions may be visualized on photographic film, or for more complex and detailed information, computed tomography (CT scan), fluroscopy, or angiography might be used.
Before consenting to any x-ray procedure, the patient should consider the impact of existing medical conditions or medications. Sensitivities to contrast dyes may produce allergic reactions. Pregnant women or those who suspect they might be pregnant should consult a physician prior to x-ray treatments to avoid injury to the fetus. Nursing mothers may be required to store enough milk to last for 48 hours following certain procedures. Patient age should always be taken into consideration when choosing the type and intensity of x ray. Patients should be aware that some prescribed cancer medications act as radiosensitizers and amplify the effect of x rays. Any patient with a suppressed immune system or diabetes may require special x-ray procedures.
X-ray procedures are administered in a hospital orclinical setting. Most procedures may be conducted on an outpatient basis. The time required for the procedure may vary from a few minutes to more than an hour. There is little or no discomfort associated with diagnostic x rays. The general procedure for diagnostic x rays include:
- proper positioning and shielding of the patient
- administering contrast dyes, if necessary
- administering radiation
- review of the films by a technician to insure proper imaging
- Scheduling a time to review the films with the radiolo-gist. However, if fluoroscopy or angiography is used, the procedure is dynamic (in motion), and the radiolo-gist is present during the x ray administration.
- dismissal of the patient
Diagnostic x rays require little preparation. The patient may be required to abstain from food and liquids for a certain period prior to the x ray. For some x rays, enemas may be necessary or a contrast agent may be administered immediately prior to or during the procedure.
For non-invasive diagnostic x-ray procedures, the patient is dismissed immediately after the films have been reviewed, and little or no aftercare is necessary.
A general rule for x rays suggests that the beneficial effects of x rays far exceed the risks involved. As a result of certified training and strict guideline compliance, risks from technical application are essentially nonexistent. However, for any x-ray procedure, radiation exposure is always a concern, and although uncommon, the risk of infection during invasive techniques can not be discounted.
Diagnostic x rays provide detailed information that the physician can use to determine the best approach to correct or control a medical problem. Normal results would indicate no existing abnormalities.
Abnormal results would indicate irregularities such as a tumor, an enlarged lymph node, or pleural effusion . Although highly unlikely, diagnostic x-ray films can be misread and the wrong diagnosis made.
See Also Barium enema; Bone survey; CT-guided biopsy; Imaging studies; Intravenous urography; Lymphangiography; Nephrostomy; Pain management; Percutaneous transhepatic cholangiography; Radiation therapy; Stereotactic needle biopsy; Upper GI series
Brant, William E., and Clyde A. Helms, ed. Fundamentals of Diagnostic Radiology. Second Edition. Baltimore:Williams & Wilkins, 1999.
Cope, Constantine, Dana R. Burke, and Steven Meranze, eds. Atlas of Interventional Radiology. New York: Gower Medical Publishing, 1990.
Henchke, Claudia, et al. "Early Lung Cancer Action Project:Overall Design and Findings from Baseline Screening."Lancet 354 (July 1999): 99-105.
Marchant, Joan. "Pixels Join Cancer Fight." The Guardian. Dec. 1999. 21 April 2001. 28 June 2001 <http://www.guardianunlimited.co.uk>
Jane Taylor-Jones, M.S.
—A radiographic technique in which an opaque contrast material is injected into a blood vessel for the purpose of identifying its anatomy on x ray.
Computed tomography (CT)
—A special radiographic technique that uses a computer to convert multiple x-ray images into a two dimensional cross-sectional image.
—A radiopaque dye that allows enhancement of the anatomy demonstrable with conventional x ray.
—X-ray imaging of moving anatomic structures.
—The delivery of normal genes or genetically altered cells to the site of a tumor.
—Diagnostic and therapeutic x-ray procedures that are invasive or surgical in nature but do not require the use of general anesthesia.
—The accumulation of fluid in the pleural space, the region between the outer surface of each lung.
—A physician specially trained in the use of x-rays for diagnostic and therapy purposes.
QUESTIONS TO ASK THE DOCTOR
- What type of x-ray procedure is best to diagnosis my condition?
- Will the procedure or treatment hurt?
- How long will it take each time and how many treatments are required?
- What are my chances for a complete recovery?
- Are these procedures covered by insurance?
X ray, invisible, highly penetrating electromagnetic radiation of much shorter wavelength (higher frequency) than visible light. The wavelength range for X rays is from about 10-8 m to about 10-11 m, or from less than a billionth of an inch to less than a trillionth of an inch; the corresponding frequency range is from about 3 × 1016 Hz to about 3 × 1019 Hz (1 Hz = 1 cps).
Production of X Rays
An important source of X rays is synchrotron radiation. X rays are also produced in a highly evacuated glass bulb, called an X-ray tube, that contains essentially two electrodes—an anode made of platinum, tungsten, or another heavy metal of high melting point, and a cathode. When a high voltage is applied between the electrodes, streams of electrons (cathode rays) are accelerated from the cathode to the anode and produce X rays as they strike the anode.
Two different processes give rise to radiation of X-ray frequency. In one process radiation is emitted by the high-speed electrons themselves as they are slowed or even stopped in passing near the positively charged nuclei of the anode material. This radiation is often called brehmsstrahlung [Ger.,=braking radiation]. In a second process radiation is emitted by the electrons of the anode atoms when incoming electrons from the cathode knock electrons near the nuclei out of orbit and they are replaced by other electrons from outer orbits. The spectrum of frequencies given off with any particular anode material thus consists of a continuous range of frequencies emitted in the first process, and superimposed on it a number of sharp peaks of intensity corresponding to discrete frequencies at which X rays are emitted in the second process. The sharp peaks constitute the X-ray line spectrum for the anode material and will differ for different materials.
Applications of X Rays
Most applications of X rays are based on their ability to pass through matter. This ability varies with different substances; e.g., wood and flesh are easily penetrated, but denser substances such as lead and bone are more opaque. The penetrating power of X rays also depends on their energy. The more penetrating X rays, known as hard X rays, are of higher frequency and are thus more energetic, while the less penetrating X rays, called soft X rays, have lower energies. X rays that have passed through a body provide a visual image of its interior structure when they strike a photographic plate or a fluorescent screen; the darkness of the shadows produced on the plate or screen depends on the relative opacity of different parts of the body.
Photographs made with X rays are known as radiographs or skiagraphs. Radiography has applications in both medicine and industry, where it is valuable for diagnosis and nondestructive testing of products for defects. Fluoroscopy is based on the same techniques, with the photographic plate replaced by a fluorescent screen (see fluorescence; fluoroscope); its advantages over radiography in time and cost are balanced by some loss in sharpness of the image. X rays are also used with computers in CAT (computerized axial tomography) scans to produce cross-sectional images of the inside of the body.
Another use of radiography is in the examination and analysis of paintings, where studies can reveal such details as the age of a painting and underlying brushstroke techniques that help to identify or verify the artist. X rays are used in several techniques that can provide enlarged images of the structure of opaque objects. These techniques, collectively referred to as X-ray microscopy or microradiography, can also be used in the quantitative analysis of many materials. One of the dangers in the use of X rays is that they can destroy living tissue and can cause severe skin burns on human flesh exposed for too long a time. This destructive power is used in X-ray therapy to destroy diseased cells.
Discovery and Early Scientific Use
X rays were discovered in 1895 by W. C. Roentgen, who called them X rays because their nature was at first unknown; they are sometimes also called Roentgen, or Röntgen, rays. X-ray line spectra were used by H. G. J. Moseley in his important work on atomic numbers (1913) and also provided further confirmation of the quantum theory of atomic structure. Also important historically is the discovery of X-ray diffraction by Max von Laue (1912) and its subsequent application by W. H. and W. L. Bragg to the study of crystal structure.
See D. Graham and T. Eddie, X-ray Techniques in Art Galleries and Museums (1985); B. H. Kevles, Naked to the Bone: Medical Imaging in the Twentieth Century (1997).
X-rays are electromagnetic waves, like light waves, but with a wavelength about 1,000 times smaller. Because of this very short wavelength, X-rays can easily penetrate low-density material, such as flesh. They are reflected or absorbed, however, by high-density material such as bone. The picture made by an X-ray machine shows the denser materials (like bones) as dark areas.
In 1895 German physicist Wilhelm Roentgen (1845-1923) was experimenting with a cathode ray tube. The tube produced weak rays that caused a screen to fluoresce (glow). To create a controlled environment, Rontgen placed the cathode tube in a black cardboard box that was too thick for cathode rays to penetrate. Once the cathode ray tube was turned on, however, he noticed that another screen across the room began to glow. Since this second screen was too far from the tube for cathode rays to reach, especially through a layer of cardboard, Roentgen realized that he had discovered a new type of ray.
Through experimentation Roentgen found that this new ray was able to penetrate even the thick walls of his laboratory. Roentgen delivered a paper detailing his findings on December 28,1895. In the paper he admitted that he did not know the precise nature of these new rays. He chose to name them "X-rays," since "X" is the mathematical symbol for the unknown.
Few discoveries have been accompanied by as much fanfare as the X-ray. During the 12 months following the publication of Roentgen's paper, more than 1,000 books and articles were written on the subject. The number of publications rose to more than 10,000 before 1910.
A Diagnostic Tool
The penetrating power of X-rays to reveal bone structure was immediately recognized as a new medical diagnostic tool. Not all the excitement was positive, however. Many people considered the X-ray machine's ability to look through walls and doors an end to privacy. In fact, opera houses banned the use of X-ray binoculars in order to prevent patrons from peering beneath the actresses' costumes. Nevertheless, more rational minds eventually prevailed. Roentgen was awarded the first Nobel Prize for Physics in 1901.
Practical Uses of X-rays
The first medical use of X-rays came in 1896. It was American physiologist Walter Bradford Cannon who used a fluorescent screen to follow the path of barium sulfate through an animal's digestive system. This was possible only after Thomas Alva Edison invented the X-ray fluoroscope that same year. Soon after, physicians worldwide began using X-rays on humans, usually to examine bone fractures or to search for foreign objects such as bullets.
By 1970 most Americans were receiving at least one X-ray exam every year from physicians and dentists. However, recent evidence has shown that overexposure to X-rays can lead to the development of leukemia. Many doctors now recommend X-ray exams only when absolutely necessary
Ironically, the harmful side effects of X-ray scanning have suggested yet another use for the procedure called radiotherapy. In this therapy, very high frequency X-rays ("hard rays") are used to destroy cancer cells. Radiotherapy is most often used in conjunction with chemotherapy (cancer medicine that is taken by mouth).
X-Rays in Everyday Life
One of the most familiar X-ray machines is the baggage scanner found at airport terminals. This low-power X-ray device is placed over a conveyor belt, where it scans passengers' luggage. The machine used in this type of scanner must operate at a very specific frequency. It must be high enough to penetrate hard-shell baggage but low enough to prevent the accidental exposure of camera film.
[See also Barium ; X-ray crystallography ; X-ray machine ]
X-ray / ˈeks ˌrā/ (also x-ray or X ray) • n. 1. electromagnetic radiation of high energy and very short wavelength (between ultraviolet light and gamma rays) that is able to pass through many materials opaque to light. ∎ [as adj.] inf. denoting an apparent or supposed faculty for seeing beyond an outward form: you didn't need X-ray eyes to know what was going on. 2. a photographic or digital image of the internal composition of something, esp. a part of the body, produced by X-rays being passed through it. 3. a code word representing the letter X, used in radio communication. • v. [tr.] photograph or examine with X-rays: luggage in the hold is X-rayed.
Discovered in 1895 by German physicist Wilhelm K. Roentgen, x rays are a form of electromagnetic radiation, widely used in medicine, industry, metal detectors, and scientific research. X rays are most commonly used by doctors and dentists to make pictures of bones, teeth, and internal organs in order to find breaks in bones, evidence of disease, and cavities in teeth.
Since x rays are a form of ionizing radiation , they can be very dangerous. They penetrate into, and are absorbed by, plants and animals and can age, damage, and destroy living tissue. They can also cause skin burns, genetic mutations, cancer , and death at high levels of exposure. The effects of ionizing radiation tend to be cumulative, and every dose adds to the possibility of further damage.
Some authorities feel that people should try to minimize their exposure to such radiation and avoid being xrayed unless absolutely necessary. This is especially true of pregnant women, since studies show a much higher rate of childhood leukemia and other diseases among children who were exposed to x rays in utero. Ironically, fear of malpractice suits has prompted many doctors to increase the number of x rays performed while examining patients for disease.
See also Radiation exposure