Pre-Röntgen observations and researchBefore their discovery in 1895, X-rays were just a type of unidentified radiation emanating from experimental s. They were noticed by scientists investigating s produced by such tubes, which are energetic beams that were first observed in 1869. Many of the early s (invented around 1875) undoubtedly radiated X-rays, because early researchers noticed effects that were attributable to them, as detailed below. Crookes tubes created free electrons by of the residual air in the tube by a high DC of anywhere between a few s and 100 kV. This voltage accelerated the electrons coming from the to a high enough velocity that they created X-rays when they struck the or the glass wall of the tube. The earliest experimenter thought to have (unknowingly) produced X-rays was actually William Morgan. In 1785, he presented a paper to the describing the effects of passing electrical currents through a partially evacuated glass tube, producing a glow created by X-rays. This work was further explored by and his assistant . When physics professor created his "electric photography", he also unknowingly generated and detected X-rays. From 1886 to 1888, he had studied in the laboratory in Berlin, where he became familiar with the cathode rays generated in vacuum tubes when a voltage was applied across separate electrodes, as previously studied by and . His letter of January 6, 1893 (describing his discovery as "electric photography") to The was duly published and an article entitled ''Without Lens or Light, Photographs Taken With Plate and Object in Darkness'' appeared in the . Starting in 1888, Philipp Lenard conducted experiments to see whether cathode rays could pass out of the Crookes tube into the air. He built a Crookes tube with a "window" at the end made of thin aluminium, facing the cathode so the cathode rays would strike it (later called a "Lenard tube"). He found that something came through, that would expose photographic plates and cause fluorescence. He measured the penetrating power of these rays through various materials. It has been suggested that at least some of these "Lenard rays" were actually X-rays. In 1889, -born , a lecturer in experimental physics at the Prague Polytechnic who since 1877 had been constructing various designs of s to investigate their properties, published a paper on how sealed photographic plates became dark when exposed to the emanations from the tubes. formulated mathematical equations for X-rays. He postulated a dispersion theory before Röntgen made his discovery and announcement. He based it on the electromagnetic theory of light. However, he did not work with actual X-rays. In 1894, noticed damaged film in his lab that seemed to be associated with Crookes tube experiments and began investigating this invisible, . After Röntgen identified the X-ray, Tesla began making X-ray images of his own using high voltages and tubes of his own design, as well as Crookes tubes.
Discovery by RöntgenOn November 8, 1895, physics professor stumbled on X-rays while experimenting with Lenard tubes and s and began studying them. He wrote an initial report "On a new kind of ray: A preliminary communication" and on December 28, 1895, submitted it to 's Physical-Medical Society journal. This was the first paper written on X-rays. Röntgen referred to the radiation as "X", to indicate that it was an unknown type of radiation. The name stuck, although (over Röntgen's great objections) many of his colleagues suggested calling them Röntgen rays. They are still referred to as such in many languages, including , , , , , , , , , , , Latvian, , , , , , and . Röntgen received the first for his discovery. There are conflicting accounts of his discovery because Röntgen had his lab notes burned after his death, but this is a likely reconstruction by his biographers: Röntgen was investigating cathode rays from a Crookes tube which he had wrapped in black cardboard so that the visible light from the tube would not interfere, using a screen painted with barium . He noticed a faint green glow from the screen, about away. Röntgen realized some invisible rays coming from the tube were passing through the cardboard to make the screen glow. He found they could also pass through books and papers on his desk. Röntgen threw himself into investigating these unknown rays systematically. Two months after his initial discovery, he published his paper. Röntgen discovered their medical use when he made a picture of his wife's hand on a photographic plate formed due to X-rays. The photograph of his wife's hand was the first photograph of a human body part using X-rays. When she saw the picture, she said "I have seen my death." The discovery of X-rays stimulated a veritable sensation. Röntgen's biographer Otto Glasser estimated that, in 1896 alone, as many as 49 essays and 1044 articles about the new rays were published. This was probably a conservative estimate, if one considers that nearly every paper around the world extensively reported about the new discovery, with a magazine such as ''Science'' dedicating as many as 23 articles to it in that year alone. Sensationalist reactions to the new discovery included publications linking the new kind of rays to occult and paranormal theories, such as telepathy.
Advances in radiologyRöntgen immediately noticed X-rays could have medical applications. Along with his 28 December Physical-Medical Society submission, he sent a letter to physicians he knew around Europe (January 1, 1896). News (and the creation of "shadowgrams") spread rapidly with Scottish electrical engineer being the first after Röntgen to create an X-ray (of a hand). Through February, there were 46 experimenters taking up the technique in North America alone. The first use of X-rays under clinical conditions was by John Hall-Edwards in , on 11 January 1896, when he radiographed a needle stuck in the hand of an associate. On February 14, 1896, Hall-Edwards was also the first to use X-rays in a surgical operation. In early 1896, several weeks after Röntgen's discovery, Ivan Romanovich Tarkhanov irradiated frogs and insects with X-rays, concluding that the rays "not only photograph, but also affect the living function". At around the same time, the zoological illustrator James Green began to use X-rays to examine fragile specimens. first mentioned this work in a paper he delivered before the in May 1896. The book ''Sciagraphs of British Batrachians and Reptiles'' (sciagraph is an obsolete name for an X-ray photograph), by Green and James H. Gardiner, with a foreword by Boulenger, was published in 1897. The first medical X-ray made in the United States was obtained using a discharge tube of Pului's design. In January 1896, on reading of Röntgen's discovery, Frank Austin of tested all of the discharge tubes in the physics laboratory and found that only the Pului tube produced X-rays. This was a result of Pului's inclusion of an oblique "target" of , used for holding samples of material, within the tube. On 3 February 1896, Gilman Frost, professor of medicine at the college, and his brother Edwin Frost, professor of physics, exposed the wrist of Eddie McCarthy, whom Gilman had treated some weeks earlier for a fracture, to the X-rays and collected the resulting image of the broken bone on gelatin photographic plates obtained from Howard Langill, a local photographer also interested in Röntgen's work. Many experimenters, including Röntgen himself in his original experiments, came up with methods to view X-ray images "live" using some form of luminescent screen. Röntgen used a screen coated with barium Edison dropped X-ray research around 1903, before the death of Clarence Madison Dally, one of his glassblowers. Dally had a habit of testing X-ray tubes on his own hands, developing a in them so tenacious that both arms were in a futile attempt to save his life; in 1904, he became the first known death attributed to X-ray exposure. During the time the fluoroscope was being developed, Serbian American physicist In 1901, U.S. President William McKinley was shot twice in an attempt. While one bullet only grazed his , another had lodged somewhere deep inside his and could not be found. A worried McKinley aide sent word to inventor Thomas Edison to rush an to Buffalo to find the stray bullet. It arrived but was not used. While the shooting itself had not been lethal, had developed along the path of the bullet, and McKinley died of due to bacterial infection six days later.
Hazards discoveredWith the widespread experimentation with X‑rays after their discovery in 1895 by scientists, physicians, and inventors came many stories of burns, hair loss, and worse in technical journals of the time. In February 1896, Professor John Daniel and Dr. of reported hair loss after Dr. Dudley was X-rayed. A child who had been shot in the head was brought to the Vanderbilt laboratory in 1896. Before trying to find the bullet, an experiment was attempted, for which Dudley "with his characteristic devotion to science" volunteered. Daniel reported that 21 days after taking a picture of Dudley's (with an exposure time of one hour), he noticed a bald spot in diameter on the part of his head nearest the X-ray tube: "A plate holder with the plates towards the side of the skull was fastened and a placed between the skull and the head. The tube was fastened at the other side at a distance of one-half inch  from the hair." In August 1896, Dr. HD. Hawks, a graduate of Columbia College, suffered severe hand and chest burns from an X-ray demonstration. It was reported in ''Electrical Review'' and led to many other reports of problems associated with X-rays being sent in to the publication. Many experimenters including at Edison's lab, William J. Morton, and also reported burns. Elihu Thomson deliberately exposed a finger to an X-ray tube over a period of time and suffered pain, swelling, and blistering.Kathern, Ronald L. and Ziemer, Paul L
20th century and beyondThe many applications of X-rays immediately generated enormous interest. Workshops began making specialized versions of Crookes tubes for generating X-rays and these first-generation or Crookes X-ray tubes were used until about 1920. A typical early 20th century medical X-ray system consisted of a connected to a cold cathode Crookes X-ray tube. A spark gap was typically connected to the high voltage side in parallel to the tube and used for diagnostic purposes. The spark gap allowed detecting the polarity of the sparks, measuring voltage by the length of the sparks thus determining the "hardness" of the vacuum of the tube, and it provided a load in the event the X-ray tube was disconnected. To detect the hardness of the tube, the spark gap was initially opened to the widest setting. While the coil was operating, the operator reduced the gap until sparks began to appear. A tube in which the spark gap began to spark at around was considered soft (low vacuum) and suitable for thin body parts such as hands and arms. A spark indicated the tube was suitable for shoulders and knees. An spark would indicate a higher vacuum suitable for imaging the abdomen of larger individuals. Since the spark gap was connected in parallel to the tube, the spark gap had to be opened until the sparking ceased in order to operate the tube for imaging. Exposure time for photographic plates was around half a minute for a hand to a couple of minutes for a thorax. The plates may have a small addition of fluorescent salt to reduce exposure times. Crookes tubes were unreliable. They had to contain a small quantity of gas (invariably air) as a current will not flow in such a tube if they are fully evacuated. However, as time passed, the X-rays caused the glass to absorb the gas, causing the tube to generate "harder" X-rays until it soon stopped operating. Larger and more frequently used tubes were provided with devices for restoring the air, known as "softeners". These often took the form of a small side tube that contained a small piece of , a that traps relatively large quantities of air within its structure. A small electrical heater heated the mica, causing it to release a small amount of air, thus restoring the tube's efficiency. However, the mica had a limited life, and the restoration process was difficult to control. In 1904, invented the , the first kind of . This used a that caused an to flow in a . This idea was quickly applied to X-ray tubes, and hence heated-cathode X-ray tubes, called "Coolidge tubes", completely replaced the troublesome cold cathode tubes by about 1920. In about 1906, the physicist discovered that X-rays could be scattered by gases, and that each element had a characteristic X-ray spectrum. He won the 1917 for this discovery. In 1912, , Paul Knipping, and Walter Friedrich first observed the of X-rays by crystals. This discovery, along with the early work of , , and , gave birth to the field of . In 1913, performed crystallography experiments with X-rays emanating from various metals and formulated which relates the frequency of the X-rays to the atomic number of the metal. The Coolidge X-ray tube was invented the same year by William D. Coolidge. It made possible the continuous emissions of X-rays. Modern X-ray tubes are based on this design, often employing the use of rotating targets which allow for significantly higher heat dissipation than static targets, further allowing higher quantity X-ray output for use in high powered applications such as rotational CT scanners. The use of X-rays for medical purposes (which developed into the field of ) was pioneered by Major John Hall-Edwards in . Then in 1908, he had to have his left arm amputated because of the spread of X-ray dermatitis on his arm. Medical science also used the motion picture to study human physiology. In 1913, a motion picture was made in Detroit showing a hard-boiled egg inside a human stomach. This early X-ray movie was recorded at a rate of one still image every four seconds. Dr Lewis Gregory Cole of New York was a pioneer of the technique, which he called "serial radiography". In 1918, X-rays were used in association with motion picture cameras to capture the human skeleton in motion. In 1920, it was used to record the movements of tongue and teeth in the study of languages by the Institute of Phonetics in England. In 1914, developed radiological cars to support soldiers injured in . The cars would allow for rapid X-ray imaging of wounded soldiers so battlefield surgeons could quickly and more accurately operate. From the early 1920s through to the 1950s, X-ray machines were developed to assist in the fitting of shoes and were sold to commercial shoe stores. Concerns regarding the impact of frequent or poorly controlled use were expressed in the 1950s, leading to the practice's eventual end that decade. The was developed during the 1950s. The Chandra X-ray Observatory, launched on July 23, 1999, has been allowing the exploration of the very violent processes in the universe which produce X-rays. Unlike visible light, which gives a relatively stable view of the universe, the X-ray universe is unstable. It features stars being torn apart by black holes, galactic collisions, and novae, and neutron stars that build up layers of plasma that then explode into space. An X-ray laser device was proposed as part of the presidency of Ronald Reagan, Reagan Administration's Strategic Defense Initiative in the 1980s, but the only test of the device (a sort of laser "blaster" or death ray, powered by a thermonuclear explosion) gave inconclusive results. For technical and political reasons, the overall project (including the X-ray laser) was defunded (though was later revived by the second presidency of George W. Bush, Bush Administration as National Missile Defense using different technologies). Phase-contrast X-ray imaging refers to a variety of techniques that use phase information of a coherent X-ray beam to image soft tissues. It has become an important method for visualizing cellular and histological structures in a wide range of biological and medical studies. There are several technologies being used for X-ray phase-contrast imaging, all utilizing different principles to convert phase variations in the X-rays emerging from an object into intensity variations. These include propagation-based phase contrast, Talbot effect, Talbot interferometry, refraction-enhanced imaging, and X-ray interferometry. These methods provide higher contrast compared to normal absorption-contrast X-ray imaging, making it possible to see smaller details. A disadvantage is that these methods require more sophisticated equipment, such as synchrotron or X-ray tube#Microfocus X-ray tubes, microfocus X-ray sources, X-ray optics, and high resolution X-ray detectors.
Soft and hard X-raysX-rays with high photon energy, photon energies above 5–10 keV (below 0.2–0.1 nm wavelength) are called ''hard X-rays'', while those with lower energy (and longer wavelength) are called ''soft X-rays''. The intermediate range with photon energies of several keV is often referred to as ''tender X-rays''. Due to their penetrating ability, hard X-rays are widely used to image the inside of objects, e.g., in medical radiography and airport security. The term ''X-ray'' is metonymy, metonymically used to refer to a radiographic image produced using this method, in addition to the method itself. Since the wavelengths of hard X-rays are similar to the size of atoms, they are also useful for determining crystal structures by . By contrast, soft X-rays are easily absorbed in air; the attenuation length of 600 eV (~2 nm) X-rays in water is less than 1 micrometer.
Gamma raysThere is no consensus for a definition distinguishing between X-rays and s. One common practice is to distinguish between the two types of radiation based on their source: X-rays are emitted by s, while gamma rays are emitted by the atomic nucleus. This definition has several problems: other processes also can generate these high-energy photons, or sometimes the method of generation is not known. One common alternative is to distinguish X- and gamma radiation on the basis of wavelength (or, equivalently, frequency or photon energy), with radiation shorter than some arbitrary wavelength, such as 10−11 m (0.1 Angstrom, Å), defined as gamma radiation. This criterion assigns a photon to an unambiguous category, but is only possible if wavelength is known. (Some measurement techniques do not distinguish between detected wavelengths.) However, these two definitions often coincide since the electromagnetic radiation emitted by X-ray tubes generally has a longer wavelength and lower photon energy than the radiation emitted by radioactive atomic nucleus, nuclei. Occasionally, one term or the other is used in specific contexts due to historical precedent, based on measurement (detection) technique, or based on their intended use rather than their wavelength or source. Thus, gamma-rays generated for medical and industrial uses, for example radiotherapy, in the ranges of 6–20 MeV, can in this context also be referred to as X-rays.
PropertiesX-ray photons carry enough energy to Ionization, ionize atoms and disrupt molecular bonds. This makes it a type of ionizing radiation, and therefore harmful to living tissue (biology), tissue. A very high radiation dose over a short period of time causes radiation sickness, while lower doses can give an increased risk of radiation-induced cancer. In medical imaging, this increased cancer risk is generally greatly outweighed by the benefits of the examination. The ionizing capability of X-rays can be utilized in oncology, cancer treatment to kill malignant cell (biology), cells using . It is also used for material characterization using X-ray spectroscopy. Hard X-rays can traverse relatively thick objects without being much absorption (electromagnetic radiation), absorbed or scattering, scattered. For this reason, X-rays are widely used to imaging science, image the inside of visually opaque objects. The most often seen applications are in medical radiography and airport security scanners, but similar techniques are also important in industry (e.g., industrial radiography and industrial CT scanning) and research (e.g., small animal imaging#Micro-CT, small animal CT). The penetration depth varies with several orders of magnitude over the X-ray spectrum. This allows the photon energy to be adjusted for the application so as to give sufficient Transmittance, transmission through the object and at the same time provide good contrast (vision), contrast in the image. X-rays have much shorter wavelengths than visible light, which makes it possible to probe structures much smaller than can be seen using a normal microscope. This property is used in X-ray microscopy to acquire high-resolution images, and also in to determine the positions of atoms in crystals.
Interaction with matterX-rays interact with matter in three main ways, through photoelectric effect, photoabsorption, Compton scattering, and Rayleigh scattering. The strength of these interactions depends on the energy of the X-rays and the elemental composition of the material, but not much on chemical properties, since the X-ray photon energy is much higher than chemical binding energies. Photoabsorption or photoelectric absorption is the dominant interaction mechanism in the soft X-ray regime and for the lower hard X-ray energies. At higher energies, Compton scattering dominates.
Photoelectric absorptionThe probability of a photoelectric absorption per unit mass is approximately proportional to ''Z''3/''E''3, where ''Z'' is the atomic number and ''E'' is the energy of the incident photon. This rule is not valid close to inner shell electron binding energies where there are abrupt changes in interaction probability, so called absorption edges. However, the general trend of high absorption coefficients and thus short penetration depths for low photon energies and high atomic numbers is very strong. For soft tissue, photoabsorption dominates up to about 26 keV photon energy where Compton scattering takes over. For higher atomic number substances, this limit is higher. The high amount of calcium (''Z'' = 20) in bones, together with their high density, is what makes them show up so clearly on medical radiographs. A photoabsorbed photon transfers all its energy to the electron with which it interacts, thus ionizing the atom to which the electron was bound and producing a photoelectron that is likely to ionize more atoms in its path. An outer electron will fill the vacant electron position and produce either a characteristic X-ray or an Auger electron. These effects can be used for elemental detection through X-ray spectroscopy or Auger electron spectroscopy.
Compton scatteringCompton scattering is the predominant interaction between X-rays and soft tissue in medical imaging. Compton scattering is an inelastic scattering of the X-ray photon by an outer shell electron. Part of the energy of the photon is transferred to the scattering electron, thereby ionizing the atom and increasing the wavelength of the X-ray. The scattered photon can go in any direction, but a direction similar to the original direction is more likely, especially for high-energy X-rays. The probability for different scattering angles is described by the Klein–Nishina formula. The transferred energy can be directly obtained from the scattering angle from the conservation of energy and conservation of momentum, momentum.
Rayleigh scatteringRayleigh scattering is the dominant elastic scattering mechanism in the X-ray regime. Inelastic forward scattering gives rise to the refractive index, which for X-rays is only slightly below 1.
ProductionWhenever charged particles (electrons or ions) of sufficient energy hit a material, X-rays are produced.
Production by electronsX-rays can be generated by an X-ray tube, a that uses a high voltage to accelerate the s released by a to a high velocity. The high velocity electrons collide with a metal target, the , creating the X-rays. In medical X-ray tubes the target is usually tungsten or a more crack-resistant alloy of rhenium (5%) and tungsten (95%), but sometimes molybdenum for more specialized applications, such as when softer X-rays are needed as in mammography. In crystallography, a copper target is most common, with cobalt often being used when fluorescence from iron content in the sample might otherwise present a problem. The maximum energy of the produced X-ray photon is limited by the energy of the incident electron, which is equal to the voltage on the tube times the electron charge, so an 80 kV tube cannot create X-rays with an energy greater than 80 keV. When the electrons hit the target, X-rays are created by two different atomic processes: # ''Characteristic X-ray emission'' (X-ray electroluminescence): If the electron has enough energy, it can knock an orbital electron out of the inner electron shell of the target atom. After that, electrons from higher energy levels fill the vacancies, and X-ray photons are emitted. This process produces an emission spectrum of X-rays at a few discrete frequencies, sometimes referred to as spectral lines. Usually, these are transitions from the upper shells to the K shell (called K lines), to the L shell (called L lines) and so on. If the transition is from 2p to 1s, it is called Kα, while if it is from 3p to 1s it is Kβ. The frequencies of these lines depend on the material of the target and are therefore called characteristic lines. The Kα line usually has greater intensity than the Kβ one and is more desirable in diffraction experiments. Thus the Kβ line is filtered out by a filter. The filter is usually made of a metal having one proton less than the anode material (e.g., Ni filter for Cu anode or Nb filter for Mo anode). # ''Bremsstrahlung'': This is radiation given off by the electrons as they are scattered by the strong electric field near the high-''Z'' (proton number) nuclei. These X-rays have a continuous spectrum. The frequency of bremsstrahlung is limited by the energy of incident electrons. So, the resulting output of a tube consists of a continuous bremsstrahlung spectrum falling off to zero at the tube voltage, plus several spikes at the characteristic lines. The voltages used in diagnostic X-ray tubes range from roughly 20 kV to 150 kV and thus the highest energies of the X-ray photons range from roughly 20 keV to 150 keV. Both of these X-ray production processes are inefficient, with only about one percent of the electrical energy used by the tube converted into X-rays, and thus most of the electric power consumed by the tube is released as waste heat. When producing a usable flux of X-rays, the X-ray tube must be designed to dissipate the excess heat. A specialized source of X-rays which is becoming widely used in research is synchrotron radiation, which is generated by particle accelerators. Its unique features are X-ray outputs many orders of magnitude greater than those of X-ray tubes, wide X-ray spectra, excellent collimation, and linear polarization. Short nanosecond bursts of X-rays peaking at 15 keV in energy may be reliably produced by peeling pressure-sensitive adhesive tape from its backing in a moderate vacuum. This is likely to be the result of recombination of electrical charges produced by triboelectric effect, triboelectric charging. The intensity of X-ray triboluminescence is sufficient for it to be used as a source for X-ray imaging.
Production by fast positive ionsX-rays can also be produced by fast protons or other positive ions. The proton-induced X-ray emission or particle-induced X-ray emission is widely used as an analytical procedure. For high energies, the production cross section (physics), cross section is proportional to ''Z12Z2−4'', where ''Z1'' refers to the atomic number of the ion, ''Z2'' refers to that of the target atom. An overview of these cross sections is given in the same reference.
Production in lightning and laboratory dischargesX-rays are also produced in lightning accompanying terrestrial gamma-ray flashes. The underlying mechanism is the acceleration of electrons in lightning related electric fields and the subsequent production of photons through Bremsstrahlung. This produces photons with energies of some few electronvolt, keV and several tens of MeV. In laboratory discharges with a gap size of approximately 1 meter length and a peak voltage of 1 MV, X-rays with a characteristic energy of 160 keV are observed. A possible explanation is the encounter of two streamer discharge, streamers and the production of high-energy Runaway electrons, run-away electrons; however, microscopic simulations have shown that the duration of electric field enhancement between two streamers is too short to produce a significant number of run-away electrons. Recently, it has been proposed that air perturbations in the vicinity of streamers can facilitate the production of run-away electrons and hence of X-rays from discharges.
DetectorsX-ray detectors vary in shape and function depending on their purpose. Imaging detectors such as those used for radiography were originally based on photographic plates and later photographic film, but are now mostly replaced by various digital data, digital detector types such as image plates and flat panel detectors. For radiation protection direct exposure hazard is often evaluated using ionization chambers, while dosimeters are used to measure the radiation dose a person has been exposed to. X-ray energy spectrum, spectra can be measured either by energy dispersive or wavelength dispersive spectrometers. For X-ray diffraction applications, such as , hybrid pixel detector, hybrid photon counting detectors are widely used.
Medical usesSince Röntgen's discovery that X-rays can identify bone structures, X-rays have been used for medical imaging. The first medical use was less than a month after his paper on the subject. Up to 2010, five billion medical imaging examinations had been conducted worldwide. Radiation exposure from medical imaging in 2006 made up about 50% of total ionizing radiation exposure in the United States.
Projectional radiographsProjectional radiography is the practice of producing two-dimensional images using X-ray radiation. Bones contain a high concentration of calcium, which, due to its relatively high atomic number, absorbs X-rays efficiently. This reduces the amount of X-rays reaching the detector in the shadow of the bones, making them clearly visible on the radiograph. The lungs and trapped gas also show up clearly because of lower absorption compared to tissue, while differences between tissue types are harder to see. Projectional radiographs are useful in the detection of pathology of the bone, skeletal system as well as for detecting some disease processes in soft tissue. Some notable examples are the very common chest radiograph, chest X-ray, which can be used to identify lung diseases such as pneumonia, lung cancer, or pulmonary edema, and the abdominal x-ray, which can detect bowel obstruction, bowel (or intestinal) obstruction, free air (from visceral perforations), and free fluid (in ascites). X-rays may also be used to detect pathology such as gallstones (which are rarely radiodensity, radiopaque) or kidney stones which are often (but not always) visible. Traditional plain X-rays are less useful in the imaging of soft tissues such as the human brain, brain or muscle. One area where projectional radiographs are used extensively is in evaluating how an orthopedic Implant (medicine), implant, such as a knee, hip or shoulder replacement, is situated in the body with respect to the surrounding bone. This can be assessed in two dimensions from plain radiographs, or it can be assessed in three dimensions if a technique called '2D to 3D registration' is used. This technique purportedly negates projection errors associated with evaluating implant position from plain radiographs. Dental radiography is commonly used in the diagnoses of common oral problems, such as dental caries, cavities. In medical diagnostic applications, the low energy (soft) X-rays are unwanted, since they are totally absorbed by the body, increasing the radiation dose without contributing to the image. Hence, a thin metal sheet, often of aluminium, called an X-ray filter, is usually placed over the window of the X-ray tube, absorbing the low energy part in the spectrum. This is called ''hardening'' the beam since it shifts the center of the spectrum towards higher energy (or harder) X-rays. To generate an image of the cardiovascular system#Human cardiovascular system, cardiovascular system, including the arteries and veins (angiography) an initial image is taken of the anatomical region of interest. A second image is then taken of the same region after an iodinated radiocontrast agent, contrast agent has been injected into the blood vessels within this area. These two images are then digitally subtracted, leaving an image of only the iodinated contrast outlining the blood vessels. The radiology, radiologist or surgeon then compares the image obtained to normal anatomical images to determine whether there is any damage or blockage of the vessel.
Computed tomographyComputed tomography (CT scanning) is a medical imaging modality where tomography, tomographic images or slices of specific areas of the body are obtained from a large series of two-dimensional X-ray images taken in different directions. These cross-sectional images can be combined into a three-dimensional space, three-dimensional image of the inside of the body and used for diagnostic and therapeutic purposes in various medical disciplines.
FluoroscopyFluoroscopy is an imaging technique commonly used by physicians or radiation therapists to obtain real-time moving images of the internal structures of a patient through the use of a fluoroscope. In its simplest form, a fluoroscope consists of an X-ray source and a fluorescent screen, between which a patient is placed. However, modern fluoroscopes couple the screen to an X-ray image intensifier and charge-coupled device, CCD video camera allowing the images to be recorded and played on a monitor. This method may use a contrast material. Examples include cardiac catheterization (to examine for coronary circulation, coronary artery blockages) and barium swallow (to examine for esophageal disorders and swallowing disorders).
RadiotherapyThe use of X-rays as a treatment is known as and is largely used for the management (including palliation) of ; it requires higher radiation doses than those received for imaging alone. X-rays beams are used for treating skin cancers using lower energy X-ray beams while higher energy beams are used for treating cancers within the body such as brain, lung, prostate, and breast.
Adverse effectsDiagnostic X-rays (primarily from CT scans due to the large dose used) increase the risk of developmental problems and in those exposed. X-rays are classified as a carcinogen by both the World Health Organization's International Agency for Research on Cancer and the U.S. government. It is estimated that 0.4% of current cancers in the United States are due to computed tomography (CT scans) performed in the past and that this may increase to as high as 1.5–2% with 2007 rates of CT usage. Experimental and epidemiological data currently do not support the proposition that there is a linear no-threshold model, threshold dose of radiation below which there is no increased risk of cancer. However, this is under increasing doubt. It is estimated that the additional radiation from diagnostic X-rays will increase the average person's cumulative risk of getting cancer by age 75 by 0.6–3.0%. The amount of absorbed radiation depends upon the type of X-ray test and the body part involved. CT and fluoroscopy entail higher doses of radiation than do plain X-rays. To place the increased risk in perspective, a plain chest X-ray will expose a person to the same amount from background radiation that people are exposed to (depending upon location) every day over 10 days, while exposure from a dental X-ray is approximately equivalent to 1 day of environmental background radiation.Radiologyinfo.org
Other usesOther notable uses of X-rays include: * in which the pattern produced by the of X-rays through the closely spaced lattice of atoms in a crystal is recorded and then analysed to reveal the nature of that lattice. A related technique, fiber diffraction, was used by Rosalind Franklin to discover the double helix, double helical structure of DNA. *X-ray astronomy, which is an observational branch of astronomy, which deals with the study of X-ray emission from celestial objects. *X-ray microscope, X-ray microscopic analysis, which uses in the soft X-ray band to produce images of very small objects. *X-ray fluorescence, a technique in which X-rays are generated within a specimen and detected. The outgoing energy of the X-ray can be used to identify the composition of the sample. *Industrial radiography uses X-rays for inspection of industrial parts, particularly welding, welds. *Radiography of cultural objects, most often x-rays of paintings to reveal underdrawing, pentimenti alterations in the course of painting or by later restorers, and sometimes previous paintings on the support. Many pigments such as lead white show well in radiographs. *X-ray spectromicroscopy has been used to analyse the reactions of pigments in paintings. For example, in analysing colour degradation in the paintings of Vincent van Gogh, van Gogh. *Authentication and quality control of packaged items. *Industrial CT (computed tomography), a process that uses X-ray equipment to produce three-dimensional representations of components both externally and internally. This is accomplished through computer processing of projection images of the scanned object in many directions. *Airport security luggage scanners use X-rays for inspecting the interior of luggage for security threats before loading on aircraft. *Border control truck scanners and NYPD X-ray vans, domestic police departments use X-rays for inspecting the interior of trucks. *X-ray art and fine art photography, artistic use of X-rays, for example the works by Stane Jagodič *X-ray hair removal, a method popular in the 1920s but now banned by the FDA. *Shoe-fitting fluoroscopes were popularized in the 1920s, banned in the US in the 1960s, in the UK in the 1970s, and later in continental Europe. *Roentgen stereophotogrammetry is used to track movement of bones based on the implantation of markers *X-ray photoelectron spectroscopy is a chemical analysis technique relying on the photoelectric effect, usually employed in surface science. *Radiation implosion is the use of high energy X-rays generated from a fission explosion (an A-bomb) to compress nuclear fuel to the point of fusion ignition (an H-bomb).
VisibilityWhile generally considered invisible to the human eye, in special circumstances X-rays can be visible. Brandes, in an experiment a short time after Wilhelm Röntgen, Röntgen's landmark 1895 paper, reported after dark adaptation and placing his eye close to an X-ray tube, seeing a faint "blue-gray" glow which seemed to originate within the eye itself. Upon hearing this, Röntgen reviewed his record books and found he too had seen the effect. When placing an X-ray tube on the opposite side of a wooden door Röntgen had noted the same blue glow, seeming to emanate from the eye itself, but thought his observations to be spurious because he only saw the effect when he used one type of tube. Later he realized that the tube which had created the effect was the only one powerful enough to make the glow plainly visible and the experiment was thereafter readily repeatable. The knowledge that X-rays are actually faintly visible to the dark-adapted naked eye has largely been forgotten today; this is probably due to the desire not to repeat what would now be seen as a recklessly dangerous and potentially harmful experiment with ionizing radiation. It is not known what exact mechanism in the eye produces the visibility: it could be due to conventional detection (excitation of rhodopsin molecules in the retina), direct excitation of retinal nerve cells, or secondary detection via, for instance, X-ray induction of phosphorescence in the eyeball with conventional retinal detection of the secondarily produced visible light. Though X-rays are otherwise invisible, it is possible to see the of the air molecules if the intensity of the X-ray beam is high enough. The beamline from the wiggler (synchrotron), wiggler at th
Units of measure and exposureThe measure of X-rays ionization, ionizing ability is called the exposure: * The coulomb per kilogram (C/kg) is the Systeme International, SI unit of ionizing radiation exposure, and it is the amount of radiation required to create one coulomb of charge of each polarity in one kilogram of matter. * The Roentgen (unit), roentgen (R) is an obsolete traditional unit of exposure, which represented the amount of radiation required to create one electrostatic unit of charge of each polarity in one cubic centimeter of dry air. 1 roentgen = . However, the effect of ionizing radiation on matter (especially living tissue) is more closely related to the amount of energy deposited into them rather than the electric charge, charge generated. This measure of energy absorbed is called the absorbed dose: * The gray (unit), gray (Gy), which has units of (joules/kilogram), is the SI unit of absorbed dose, and it is the amount of radiation required to deposit one joule of energy in one kilogram of any kind of matter. * The rad (unit), rad is the (obsolete) corresponding traditional unit, equal to 10 millijoules of energy deposited per kilogram. 100 rad = 1 gray. The equivalent dose is the measure of the biological effect of radiation on human tissue. For X-rays it is equal to the absorbed dose. * The Roentgen equivalent man (rem) is the traditional unit of equivalent dose. For X-rays it is equal to the Rad (unit), rad, or, in other words, 10 millijoules of energy deposited per kilogram. 100 rem = 1 Sv. * The sievert (Sv) is the SI unit of equivalent dose, and also of effective dose (radiation), effective dose. For X-rays the "equivalent dose" is numerically equal to a Gray (unit), Gray (Gy). 1 Sv = 1 Gy. For the "effective dose" of X-rays, it is usually not equal to the Gray (Gy).
See also* Backscatter X-ray * Detective quantum efficiency * High-energy X-rays * Macintyre's X-Ray Film – 1896 documentary radiography film * N ray * Neutron radiation * NuSTAR * Radiographer * Reflection (physics) * Resonant inelastic X-ray scattering (RIXS) * Small-angle X-ray scattering (SAXS) * The X-Rays – 1897 British short silent comedy film * X-ray absorption spectroscopy * X-ray marker * X-ray nanoprobe * X-ray reflectivity * X-ray vision * X-ray welding
External links* * * *