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Fluoroscopy (), informally referred to as " fluoro", is an imaging technique that uses to obtain real-time moving images of the interior of an object. In its primary application of medical imaging, a fluoroscope () allows a surgeon to see the internal anatomy and physiology of a patient, so that the pumping action of the heart or the motion of swallowing, for example, can be watched. This is useful for both diagnosis and therapy and occurs in general radiology, interventional radiology, and image-guided surgery.
In its simplest form, a fluoroscope consists of an X-ray generator and a fluorescence screen, between which a patient is placed. However, since the 1950s most fluoroscopes have included X-ray image intensifiers and as well, to improve the image's visibility and make it available on a remote display screen. For many decades, fluoroscopy tended to produce live pictures that were not recorded, but since the 1960s, as technology improved, recording and playback became the norm.
Fluoroscopy is similar to radiography and X-ray computed tomography (X-ray CT) in that it generates images using X-rays. The original difference was that radiography fixed still images on film, whereas fluoroscopy provided live moving pictures that were not stored. However, modern radiography, CT, and fluoroscopy now use digital imaging with image analysis software and data storage and retrieval. Compared to other x-ray imaging modalities the source projects from below leading to horizontally mirrored images, and in keeping with historical displays the grayscale remains inverted (radiodense objects such as bones are dark whereas traditionally they would be bright).
As the X-rays pass through the patient, they are attenuation by varying amounts as they refraction or reflect off the different tissues of the body, casting an X-ray shadow of the radiodensity tissues (such as bone tissue) on the fluorescent screen. Images on the screen are produced as the unattenuated or mildly attenuated X-rays from radiodensity tissues interact with atoms in the screen through the photoelectric effect, giving their energy to the . While much of the energy given to the electrons is dissipated as heat, a fraction of it is given off as visible light.
Early radiologists would adapt their eyes to view the dim fluoroscopic images by sitting in darkened rooms, or by wearing red adaptation goggles. After the development of X-ray image intensifiers, the images were brightness enough to see without goggles under normal available light. Image Intensifiers are still being used to this day (2023) with many new models still using II (Image Intensifier) as its method of acquiring the image which is still popular due to lower cost compared to Flat Panel Detectors and there have been many debates on whether II or Flat Detector is more sensitive to X-Ray, which results in lower X-Ray Dosage used. (Depending upon what type of technology / panel is being used influences this answer greatly)
Nowadays, in all forms of digital X-ray imaging (radiography, fluoroscopy, and CT) the conversion of X-ray energy into visible light can be achieved by the same types of electronic sensors, such as flat panel detectors, which convert the X-ray energy into electrical signals: small bursts of electric current that convey information that a computer can analyze, store, and output as images. As fluorescence is a special case of luminescence, digital X-ray imaging is conceptually similar to digital gamma ray imaging (scintigraphy, SPECT, and PET) in that in both of these imaging mode families, the information conveyed by the variable attenuation of invisible electromagnetic radiation as it passes through tissues with various radiodensities is converted by an electronic sensor into an electric signal that is processed by a computer and output as a visible-light image.
In the late 1890s, Thomas Edison began investigating materials for ability to fluoresce when X-rayed, and by the turn of the century he had invented a fluoroscope with sufficient image intensity to be commercialized. Edison had quickly discovered that calcium tungstate screens produced brighter images. Edison, however, abandoned his research in 1903 because of the health hazards that accompanied the use of these early devices. Clarence Dally, a glass blower of lab equipment and tubes at Edison's laboratory was repeatedly exposed, developing radiation poisoning, later dying from an aggressive cancer. Edison himself damaged an eye in testing these early fluoroscopes.New York World "Edison Fears Hidden Perils of the X Rays" Monday, August 3, 1903, page 1
During this infant commercial development, many incorrectly predicted that the moving images of fluoroscopy would completely replace roentgenographs (radiographic still image films), but the then superior diagnostic quality of the roentgenograph and their already alluded-to safety enhancement of lower radiation dose via shorter exposure prevented this from occurring. Another factor was that plain films inherently offered recording of the image in a simple and inexpensive way, whereas recording and playback of fluoroscopy remained a more complex and expensive proposition for decades to come (discussed in detail below).
Red adaptation goggles were developed by Wilhelm Trendelenburg in 1916 to address the problem of dark adaptation of the eyes, previously studied by Antoine Beclere. The resulting red light from the goggles' filtration correctly sensitized the physician's eyes prior to the procedure, while still allowing him to receive enough light to function normally.
Fluoroscopy was discontinued in shoe-fitting because the radiation exposure risk outweighed the trivial benefit. Only important applications such as health care, bodily safety, food safety, nondestructive testing, and scientific research meet the risk-benefit threshold for use.
From the late 1980s onward, digital imaging technology was reintroduced to fluoroscopy after development of improved detector systems. Modern improvements in screen phosphors, digital image processing, image analysis, and flat panel detectors have allowed for increased image quality while minimizing the radiation dose to the patient. Modern fluoroscopes use caesium iodide (CsI) screens and produce noise-limited images, ensuring that the minimal radiation dose results while still obtaining images of acceptable quality.
As soon as X-rays (and their application of seeing inside the body) were discovered in the 1890s, both looking and recording were pursued. Both live moving images and recorded still images were available from the beginning with simple equipment; thus, both "looking with a fluorescent screen" ( + ) and "recording/engraving with radiation" ( + ) were immediately named with Neo-Latin words—both words are attested since 1896.
The quest for recorded moving images, though, was a more complex challenge. In the 1890s, moving pictures of any kind (whether taken with visible light or with invisible radiation) were emerging technologies. Because the word "photography" (literally "recording/engraving with light") was long since established as connotation a still-image medium, the word "cinematography" (literally "recording/engraving movement") was coined for the new medium of visible-light moving pictures. Soon, several new words were coined for achieving moving radiographic pictures. This was often done either by filming a simple fluoroscopic screen with a movie camera (variously called fluorography, cinefluorography, photofluorography, or fluororadiography) or by taking serial radiographs rapidly to serve as the frames in a movie (cineradiography). Either way, the resulting film reel could be displayed by a movie projector. Another group of techniques included various kinds of kymography, whose common theme was capturing recordings in a series of moments, with a concept similar to movie film, although not necessarily with movie-type playback; rather, the sequential images would be compared frame by frame (a distinction comparable to tile mode versus cine mode in today's CT terminology). Thus, electrokymography and roentgenkymography were among the early ways to record images from a simple fluoroscopic screen.
Television also was under early development during these decades (1890s–1920s), but even after commercial TV began widespread adoption after World War II, it remained a live-only medium for a time. In the mid-1950s, a commercialized ability to capture the moving pictures of television onto magnetic tape (with a video tape recorder) was developed. This soon led to the addition of the "" prefix to the words fluorography and fluoroscopy, with the words videofluorography and videofluoroscopy attested since 1960. In the 1970s, videotape moved from TV studios and medical imaging into the consumer market with home video via VHS and Betamax, and those formats were also incorporated into medical video equipment.
Thus, over time the cameras and recording medium for fluoroscopic imaging have progressed: The original kind of fluoroscopy, and the common kind for its first half-century of existence, simply used none, because for most diagnosis and treatment, they were not essential. For those investigations that needed to be transmitted or recorded (such as for training or research), using film (such as 16 mm film) were the medium. In the 1950s, analog electronic (at first only producing live output, but later using video tape recorders) appeared. Since the 1990s, digital camera, flat panel detectors, and storage of data to local servers or (more recently) secure cloud computing servers have been used. Late-model fluoroscopes all use digital image processing and image analysis software, which not only helps to produce optimal image clarity and contrast, but also allows that result with a minimal radiation dose (because signal processing can take tiny inputs from low radiation doses and amplifier them while to some extent also noise reduction).
Whereas the word "cine" () in general usage refers to cinema (that is, a movie) or to certain film formats (cine film) for recording such a movie, in medical usage it refers to cineradiography or, in recent decades, to any digital imaging mode that produces cine-like moving images (for example, newer CT and MRI systems can put out to either cine mode or tile mode). Cineradiography records frame rate fluoroscopic images of internal organs such as the heart taken during injection of contrast dye to better visualize regions of stenosis, or to record motility in the body's gastrointestinal tract. The predigital technology is being replaced with digital imaging systems. Some of these decrease the frame rate, but also decrease the absorbed dose of radiation to the patient. As they improve, frame rates will likely increase.
Today, owing to technological convergence, the word "fluoroscopy" is widely understood to be a hypernym of all the earlier names for moving pictures taken with X-rays, both live and recorded. Also owing to technological convergence, radiography, CT, and fluoroscopy are now all digital imaging modes using X-rays with image-analysis software and easy data storage and retrieval. Just as movies, TV, and web videos are to a substantive extent no longer separate technologies, but only variations on common underlying digital themes, so, too, are the X-ray imaging modes, and indeed, the term "X-ray imaging" is the ultimate hypernym that unites all of them, even subsuming both fluoroscopy and four-dimensional CT (4DCT), which is the newest form of moving pictures taken with X-rays. Many decades may pass before the earlier hyponyms fall into disuse, not the least because the day when 4D CT displaces all earlier forms of moving X-ray imaging may yet be distant.
Because fluoroscopy involves the use of X-rays, a form of ionizing radiation, fluoroscopic procedures pose a potential for increasing the patient's risk of radiation-induced cancer. In addition to the cancer risk and other stochastic radiation effects, deterministic radiation effects have also been observed ranging from mild erythema, equivalent of a sunburn, to more serious burns. Radiation doses to the patient depend greatly both on the size of the patient and length of the procedure, with typical skin dose rates quoted as 20–50 mGy/min. Exposure times vary depending on the procedure being performed, ranging from minutes to hours.
A study of radiation-induced skin injuries was performed in 1994 by the U.S. Food and Drug Administration (FDA) followed by an advisory to minimize further fluoroscopy-induced injuries. The problem of radiation injuries due to fluoroscopy has been further addressed in review articles in 2000 and 2010.
While deterministic radiation effects are a possibility, radiation burns are not typical in standard fluoroscopic procedures. Most procedures sufficiently long in duration to produce radiation burns are part of necessary life-saving operations.
X-ray image intensifiers generally have radiation-reducing systems such as pulsed rather than constant radiation, along with "last image hold", which "freezes" the screen and makes it available for examination without exposing the patient to unnecessary radiation.
Image intensifiers have been introduced that increase the brightness of the screen, so that the patient can be exposed to a lower dose of X-rays. Whilst this reduces the risk of ionisation occurring, it does not remove it entirely.
Modern image intensifiers no longer use a separate fluorescent screen. Instead, a caesium iodide phosphor is deposited directly on the photocathode of the intensifier tube. On a typical general-purpose system, the output image is approximately 105 times brighter than the input image. This brightness gain comprises a flux gain (amplification of photon number) and minification gain (concentration of photons from a large input screen onto a small output screen) each of about 100. This level of gain is sufficient that quantum noise, due to the limited number of X-ray photons, is a significant factor limiting image quality.
Within the XRII, five mini components make up this intensifier, which are:
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Image intensifiers are available with input diameters up to 45 cm, and a resolution of around two to three line pairs/mm.
Flat-panel detectors are considerably more expensive to purchase and repair than image intensifiers, so their use adoption is primarily in specialties that require high-speed imaging, e.g., angiography and cardiac catheterization.
Most modern injected radiographic positive contrast media are iodine-based. Iodinated contrast comes in two forms - ionic and nonionic compounds. Nonionic contrast is significantly more expensive than ionic (about three to five times the cost), but nonionic contrast tends to be safer for the patient, causing fewer allergic reactions and uncomfortable side effects such as hot sensations or flushing. Most imaging centers now use nonionic contrast exclusively, finding that the benefits to patients outweigh the expense.
Negative radiographic contrast agents are air and carbon dioxide (CO2). The latter is easily absorbed by the body and causes less spasm. It can also be injected into the blood, where air absolutely cannot due to the risk of an air embolism.
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