Radiography is animaging technique usingX-rays,gamma rays, or similar ionizing radiation and non-ionizing radiation to view the internal form of an object. Applications of radiography include medical ("diagnostic" radiography and "therapeutic radiography") andindustrial radiography. Similar techniques are used inairport security, (where "body scanners" generally usebackscatter X-ray). To create an image inconventional radiography, a beam of X-rays is produced by anX-ray generator and it is projected towards the object. A certain amount of the X-rays or other radiation are absorbed by the object, dependent on the object's density and structural composition. The X-rays that pass through the object are captured behind the object by adetector (eitherphotographic film or a digital detector). The generation of flattwo-dimensional images by this technique is calledprojectional radiography. Incomputed tomography (CT scanning), an X-ray source and its associated detectors rotate around the subject, which itself moves through the conical X-ray beam produced. Any given point within the subject is crossed from many directions by many different beams at different times. Information regarding the attenuation of these beams is collated and subjected to computation to generate two-dimensional images on three planes (axial, coronal, and sagittal) which can be further processed to produce a three-dimensional image.
Taking an X-ray image with earlyCrookes tube apparatus, late 1800s
Radiography's origins andfluoroscopy's origins can both be traced to 8 November 1895, when German physics professorWilhelm Conrad Röntgen discovered the X-ray and noted that, while it could pass through human tissue, it could not pass through bone or metal.[1] Röntgen referred to the radiation as "X", to indicate that it was an unknown type of radiation. He received the firstNobel Prize in Physics for his discovery.[2]
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:[3][4] Röntgen was investigatingcathode rays using afluorescent screen painted with bariumplatinocyanide and aCrookes tube which he had wrapped in black cardboard to shield its fluorescent glow. He noticed a faint green glow from the screen, about 1 metre away. Röntgen realized some invisible rays coming from the tube were passing through the cardboard to make the screen glow: they were passing through an opaque object to affect the film behind it.[5]
The first radiograph
Röntgen discovered X-rays' 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 ever photograph of a human body part using X-rays. When she saw the picture, she said, "I have seen my death."[5]
The first use of X-rays under clinical conditions was byJohn Hall-Edwards inBirmingham, England, on 11 January 1896, when he radiographed a needle stuck in the hand of an associate. On 14 February 1896, Hall-Edwards also became the first to use X-rays in asurgical operation.[6]
The United States saw its first medical X-ray obtained using adischarge tube ofIvan Pulyui's design. In January 1896, on reading of Röntgen's discovery, Frank Austin ofDartmouth College tested all of the discharge tubes in the physics laboratory and found that only the Pulyui tube produced X-rays. This was a result of Pulyui's inclusion of an oblique "target" ofmica, used for holding samples offluorescent 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 ongelatin photographic plates obtained from Howard Langill, a local photographer also interested in Röntgen's work.[7]
1897 sciagraph (X-ray photograph) ofPelophylax lessonae (thenRana Esculenta), from James Green & James H. Gardiner's "Sciagraphs of British Batrachians and Reptiles"
X-rays were put to diagnostic use very early; for example,Alan Archibald Campbell-Swinton opened a radiographic laboratory in the United Kingdom in 1896, before the dangers of ionizing radiation were discovered. Indeed,Marie Curie pushed for radiography to be used to treat wounded soldiers in World War I. Initially, many kinds of staff conducted radiography in hospitals, including physicists, photographers, physicians, nurses, and engineers. The medical speciality of radiology grew up over many years around the new technology. When new diagnostic tests were developed, it was natural for theradiographers to be trained in and to adopt this new technology. Radiographers now performfluoroscopy,computed tomography,mammography,ultrasound,nuclear medicine andmagnetic resonance imaging as well. Although a nonspecialist dictionary might define radiography quite narrowly as "taking X-ray images", this has long been only part of the work of "X-ray departments", radiographers, and radiologists. Initially, radiographs were known as roentgenograms,[8] whileskiagrapher (from theAncient Greek words for "shadow" and "writer") was used until about 1918 to meanradiographer. The Japanese term for the radiograph,rentogen (レントゲン), shares its etymology with the original English term.
Since the body is made up of various substances with differing densities, ionising and non-ionising radiation can be used to reveal the internal structure of the body on an image receptor by highlighting these differences usingattenuation, or in the case of ionising radiation, the absorption of X-rayphotons by the denser substances (likecalcium-rich bones). The discipline involving the study of anatomy through the use of radiographic images is known asradiographic anatomy. Medical radiography acquisition is generally carried out byradiographers, while image analysis is generally done byradiologists. Some radiographers also specialise in image interpretation. Medical radiography includes a range of modalities producing many different types of image, each of which has a different clinical application.
The creation of images by exposing an object toX-rays or other high-energy forms ofelectromagnetic radiation and capturing the resulting remnant beam (or "shadow") as a latent image is known as "projection radiography". The "shadow" may be converted to light using a fluorescent screen, which is then captured onphotographic film, it may be captured by a phosphor screen to be "read" later by a laser (CR), or it may directly activate a matrix ofsolid-state detectors (DR—similar to a very large version of aCCD in a digital camera).Bone and some organs (such aslungs) especially lend themselves to projection radiography. It is a relatively low-cost investigation with a highdiagnostic yield. The difference betweensoft andhard body parts stems mostly from the fact that carbon has a very low X-ray cross section compared to calcium.
Computed tomography or CT scan (previously known as CAT scan, the "A" standing for "axial") uses ionizing radiation (x-ray radiation) in conjunction with a computer to create images of both soft and hard tissues. These images look as though the patient was sliced like bread (thus, "tomography" – "tomo" means "slice"). Though CT uses a higher amount of ionizing x-radiation than diagnostic x-rays (both utilising X-ray radiation), with advances in technology, levels of CT radiation dose and scan times have reduced.[9] CT exams are generally short, most lasting only as long as a breath-hold,Contrast agents are also often used, depending on the tissues needing to be seen. Radiographers perform these examinations, sometimes in conjunction with a radiologist (for instance, when a radiologist performs a CT-guidedbiopsy).
DEXA, or bone densitometry, is used primarily forosteoporosis tests. It is not projection radiography, as the X-rays are emitted in two narrow beams that are scanned across the patient, 90 degrees from each other. Usually the hip (head of thefemur), lower back (lumbar spine), or heel (calcaneum) are imaged, and the bone density (amount of calcium) is determined and given a number (a T-score). It is not used for bone imaging, as the image quality is not good enough to make an accurate diagnostic image for fractures, inflammation, etc. It can also be used to measure total body fat, though this is not common. The radiation dose received fromDEXA scans is very low, much lower than projection radiography examinations.[citation needed]
Fluoroscopy is a term invented byThomas Edison during his early X-ray studies. The name refers to the fluorescence he saw while looking at a glowing plate bombarded with X-rays.[10]
The technique provides moving projection radiographs. Fluoroscopy is mainly performed to view movement (of tissue or a contrast agent), or to guide a medical intervention, such as angioplasty, pacemaker insertion, or joint repair/replacement. The last can often be carried out in the operating theatre, using a portable fluoroscopy machine called a C-arm.[11] It can move around the surgery table and make digital images for the surgeon. Biplanar Fluoroscopy works the same as single plane fluoroscopy except displaying two planes at the same time. The ability to work in two planes is important for orthopedic and spinal surgery and can reduce operating times by eliminating re-positioning.[12]
Angiography is the use of fluoroscopy to view the cardiovascular system. An iodine-based contrast is injected into the bloodstream and watched as it travels around. Since liquid blood and the vessels are not very dense, a contrast with high density (like the large iodine atoms) is used to view the vessels under X-ray. Angiography is used to findaneurysms, leaks, blockages (thromboses), new vessel growth, and placement of catheters and stents.Balloon angioplasty is often done with angiography.
Although not technically radiographic techniques due to not using X-rays, imaging modalities such asPET andMRI are sometimes grouped in radiography because theradiology department of hospitals handle all forms ofimaging. Treatment using radiation is known asradiotherapy.
Industrial radiography is a method ofnon-destructive testing where many types of manufactured components can be examined to verify the internal structure and integrity of the specimen. Industrial Radiography can be performed utilizing eitherX-rays orgamma rays. Both are forms ofelectromagnetic radiation. The difference between various forms of electromagnetic energy is related to thewavelength. X and gamma rays have the shortest wavelength and this property leads to the ability to penetrate, travel through, and exit various materials such ascarbon steel and other metals. Specific methods includeindustrial computed tomography.
Radiography may also be used inpaleontology, such as for these radiographs of theDarwinius fossilIda.
Image quality will depend on resolution and density.Resolution is the ability of an image to show closely spaced structure in the object as separate entities in the image while density is the blackening power of the image.Sharpness of a radiographic image is strongly determined by the size of the X-ray source. This is determined by the area of the electron beam hitting the anode.A large photon source results in more blurring in the final image and is worsened by an increase in image formation distance. This blurring can be measured as a contribution to themodulation transfer function of the imaging system.
Lead is the most common shield against X-rays because of its high density (11,340 kg/m3), stopping power, ease of installation and low cost. The maximum range of a high-energy photon such as an X-ray in matter is infinite; at every point in the matter traversed by the photon, there is a probability of interaction. Thus there is a very small probability of no interaction over very large distances. The shielding of photon beam is therefore exponential (with anattenuation length being close to theradiation length of the material); doubling the thickness of shielding will square the shielding effect.
Table in this section shows the recommended thickness of lead shielding in function of X-ray energy, from the Recommendations by the Second International Congress of Radiology.[17]
In response to increased concern by the public over radiation doses and the ongoing progress of best practices, The Alliance for Radiation Safety in Pediatric Imaging was formed within theSociety for Pediatric Radiology. In concert with theAmerican Society of Radiologic Technologists, theAmerican College of Radiology, and theAmerican Association of Physicists in Medicine, the Society for Pediatric Radiology developed and launched the Image Gently campaign which is designed to maintain high quality imaging studies while using the lowest doses and best radiation safety practices available on pediatric patients.[18] This initiative has been endorsed and applied by a growing list of various professional medical organizations around the world and has received support and assistance from companies that manufacture equipment used in radiology.
Following upon the success of the Image Gently campaign, the American College of Radiology, the Radiological Society of North America, the American Association of Physicists in Medicine, and the American Society of Radiologic Technologists have launched a similar campaign to address this issue in the adult population called Image Wisely.[19] TheWorld Health Organization andInternational Atomic Energy Agency (IAEA) of the United Nations have also been working in this area and have ongoing projects designed to broaden best practices and lower patient radiation dose.[20][21][22]
Contrary to advice that emphasises only conducting radiographs when in the patient's interest, recent evidence suggests that they are used more frequently when dentists are paid under fee-for-service.[23]
In medicine and dentistry,projectional radiography andcomputed tomography images generally use X-rays created byX-ray generators, which generate X-rays fromX-ray tubes. The resultant images from the radiograph (X-ray generator/machine) or CT scanner are correctly referred to as "radiograms"/"roentgenograms" and "tomograms" respectively.
Ananti-scatter grid may be placed between the patient and the detector to reduce the quantity of scattered x-rays that reach the detector. This improves the contrast resolution of the image, but also increases radiation exposure for the patient.[24]
A radiopaque anatomical side marker is added to each image. For example, if the patient has their right hand x-rayed, the radiographer includes a radiopaque "R" marker within the field of the x-ray beam as an indicator of which hand has been imaged. If a physical marker is not included, the radiographer may add the correct side marker later as part of digital post-processing.[28]
As an alternative to X-ray detectors,image intensifiers are analog devices that readily convert the acquired X-ray image into one visible on a video screen. This device is made of a vacuum tube with a wide input surface coated on the inside withcaesium iodide (CsI). When hit by X-rays, phosphor material causes thephotocathode adjacent to it to emit electrons. These electrons are then focused using electron lenses inside the intensifier to an output screen coated with phosphorescent materials. The image from the output can then be recorded via a camera and displayed.[29]
Digital devices known as array detectors are becoming more common in fluoroscopy. These devices are made of discrete pixelated detectors known asthin-film transistors (TFT) which can either workindirectly by using photo detectors that detect light emitted from a scintillator material such as CsI, ordirectly by capturing the electrons produced when the X-rays hit the detector. Direct detectors do not tend to experience the blurring or spreading effect caused by phosphorescent scintillators or by film screens since the detectors are activated directly by X-ray photons.[30]
Radiation contamination – Undesirable radioactive elements on surfaces or in gases, liquids, or solids is a problemPages displaying short descriptions of redirect targets
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Oakley, PA; Harrison, DE (2020). X-Ray Hesitancy: Patients' Radiophobic Concerns Over Medical X-rays. Dose-Response.Specific Safety Guide No. SSG-11 (Report). Vienna: International Atomic Energy Agency.doi:10.1177/1559325820959542.PMC7503016.
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