Physics, Techniques and ProceduresFluoroscopy
the common name for production of
real-time images, directly visible to the eye during an
X-ray examination. Historically, fluoroscopy was done the first time by W.C. Roentgen when he first discovered the new kind of rays in 1895. For medical purposes, the first fluoroscopy units were used as early as 1896. Until the introduction of the
image intensifier in the 1950s, the fluoroscopy units were equipped with a fluorescent screen consisting of copper activated zinc cadmium sulphide that emitted light in the yellow-green part of the visible spectrum. The fluorescent screen was covered with a lead glass in order to protect the observer. In spite of the very high doses required to produce a visible image on the screen, the light level produced was extremely faint. The examination had to be carried out in a dark room, and the
radiologist had to adapt his eyes for up to half an hour prior to examination. The fluoroscopic technique was revolutionized when the image intensifier was introduced.
The advantages of real-time imaging and the freedom to freely position the X-ray field during examination makes fluoroscopy a very powerful diagnostic tool. However, due to the length of the fluoroscopic examinations, the exposure rate must be kept very much lower than in common radiography. The exposure rate in fluoroscopy is 100200 times lower than when exposing film or storage phosphor cassettes. The visible fluoroscopic image is therefore formed using much less X-ray photons. This will result in images that suffer from a much higher level of quantum noise than in ordinary radiographs. Also, the gain of the fluoroscopic system must be very high, adding electronic noise to the image. Accordingly, the fluoroscopic image suffers from inferior spatial resolution and a high noise level when compared to common radiographs.
A modern fluoroscopic system can be produced in a large number of varieties and can accordingly be used in many fields of radiology, such as photospot imaging, spot film imaging, angiography, digital subtraction angiography DSA , gastrointestinal imaging, in connection with endoscopy, lithotripsy etc. The term fluoroscopy should not be confused with fluorography. In the latter method, high dose rates are used together with irradiation with very short X-ray pulses, such as in coronary angiography (see cinefluorography). Still, fluoroscopic equipment is used which is modified for fluorographic purposes.
Modern fluoroscopy equipment is among the most complicated and expensive systems at an X-ray department and can generally only be operated by the a fully qualified and experienced radiologist. The use of the most advanced fluoroscopic systems tend therefore to be more and more concentrated to larger X-ray departments.
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