radiography radiography radiography is an imaging technique using x-rays, gamma rays, or similar ionizing radiation and non-ionizing radiation to view the internal form of an object. applications of radiography include medical radiography ("diagnostic" and "therapeutic") and industrial radiography. similar techniques are used in airport security (where "body scanners" generally use backscatter x-ray). to create an image in conventional radiography, a beam of x-rays is produced by an x-ray generator and is projected toward the object. a certain amount of the x-rays or other radiation is 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 a detector (either photographic film or a digital detector). the generation of flat two dimensional images by this technique is called projectional radiography. in computed 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 attenuation of these beams is collated and subjected to computation to generate two dimensional images in three planes (axial, coronal, and sagittal) which can be further processed to produce a three dimensional image. a medical radiograph of a skull for the medical specialty covering all imaging modes, see radiology. for treatment using radiation, see radiotherapy. radiographyprojectional radiography of the knee in a modern x-ray machinesystemmusculoskeletalsubdivisionsinterventional, nuclear, therapeutic, paediatricsignificant diseasescancer, bone fracturessignificant testsscreening tests, x-ray, ct, mri, pet, bone scan, ultrasonography, mammography, fluoroscopyspecialistradiographer medical uses radiographyicd-9-cm87, 88.0-88.6meshd011859ops-301 code3–10...3–13, 3–20...3–26 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 using attenuation, or in the case of ionising radiation, the absorption of x-ray photons by the denser substances (like calcium-rich bones). the discipline involving the study of anatomy through the use of radiographic images is known as radiographic anatomy. medical radiography acquisition is generally carried out by radiographers, while image analysis is generally done by radiologists. 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. projectional radiography main article: projectional radiography acquisition of projectional radiography, with an x-ray generator and a detector the creation of images by exposing an object to x-rays or other high-energy forms of electromagnetic 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 on photographic film, it may be captured by a phosphor screen to be "read" later by a laser (cr), or it may directly activate a matrix of solid-state detectors (dr—similar to a very large version of a ccd in a digital camera). bone and some organs (such as lungs) especially lend themselves to projection radiography. it is a relatively low-cost investigation with a high diagnostic yield. the difference between soft and hard body parts stems mostly from the fact that carbon has a very low x-ray cross section compared to calcium. computed tomography main article: computed tomography images generated from computed tomography, including a 3d rendered image at upper left 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. 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-guided biopsy). dual energy x-ray absorptiometry main article: dual energy x-ray absorptiometry dexa, or bone densitometry, is used primarily for osteoporosis 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 the femur), 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 from dexa scans is very low, much lower than projection radiography examinations. fluoroscopy main article: fluoroscopy fluoroscopy is a term invented by thomas 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. 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. 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. angiography main article: angiography angiogram showing a transverse projection of the vertebro basilar and posterior cerebral circulation 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 find aneurysms, leaks, blockages (thromboses), new vessel growth, and placement of catheters and stents. balloon angioplasty is often done with angiography. contrast radiography main article: radiocontrast agent contrast radiography uses a radiocontrast agent, a type of contrast medium, to make the structures of interest stand out visually from their background. contrast agents are required in conventional angiography, and can be used in both projectional radiography and computed tomography (called contrast ct). other medical imaging although not technically radiographic techniques due to not using x-rays, imaging modalities such as pet and mri are sometimes grouped in radiography because the radiology department of hospitals handle all forms of imaging. treatment using radiation is known as radiotherapy. industrial radiography industrial radiography is a method of non-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 either x-rays or gamma rays. both are forms of electromagnetic radiation. the difference between various forms of electromagnetic energy is related to the wavelength. x and gamma rays have the shortest wavelength and this property leads to the ability to penetrate, travel through, and exit various materials such as carbon steel and other metals. specific methods include industrial computed tomography. radiography may also be used in paleontology, such as for these radiographs of the darwinius fossil ida. image quality image quality will depend on resolution and density. resolution is the ability 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 the modulation transfer function of the imaging system. the memory devices used in large-scale radiographic systems are also very important. they work efficiently to store the crucial data of contrast and density in the radiography image and produce the output accordingly. smaller capacity memory drives with high-density connectors are also important to deal with internal vibration or shock. radiation dose the dosage of radiation applied in radiography varies by procedure. for example, the effective dosage of a chest x-ray is 0.1 msv, while an abdominal ct is 10 msv. the american association of physicists in medicine (aapm) have stated that the "risks of medical imaging at patient doses below 50 msv for single procedures or 100 msv for multiple procedures over short time periods are too low to be detectable and may be nonexistent." other scientific bodies sharing this conclusion include the international organization of medical physicists, the un scientific committee on the effects of atomic radiation, and the international commission on radiological protection. nonetheless, radiological organizations, including the radiological society of north america (rsna) and the american college of radiology (acr), as well as multiple government agencies, indicate safety standards to ensure that radiation dosage is as low as possible. shielding x-rays generated bypeak voltages belowminimum thickness of lead 75 kv1.0 mm 100 kv1.5 mm 125 kv2.0 mm 150 kv2.5 mm 175 kv3.0 mm 200 kv4.0 mm 225 kv5.0 mm 300 kv9.0 mm 400 kv15.0 mm 500 kv22.0 mm 600 kv34.0 mm 900 kv51.0 mm 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 an attenuation length being close to the radiation 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. campaigns 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 the society for pediatric radiology. in concert with the american society of radiologic technologists, the american college of radiology, and the american 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. 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. the world health organization and international 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. provider payment 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. equipment a plain radiograph of the elbow ap radiograph of the lumbar spine a hand prepared to be x-rayed sources in medicine and dentistry, projectional radiography and computed tomography images generally use x-rays created by x-ray generators, which generate x-rays from x-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. a number of other sources of x-ray photons are possible, and may be used in industrial radiography