Fluoroscopy is an imaging technique commonly used by physicians 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 fluorescent screen between which a patient is placed. However, modern fluoroscopes couple the screen to an x-ray image intensifier and CCD video camera allowing the images to be played and recorded on a monitor.
The use of x-rays, a form of ionizing radiation, requires that the potential risks from a procedure be carefully balanced with the benefits of the procedure to the patient. While physicians always try to use low dose rates during fluoroscopic procedures, the length of a typical procedure often results in a relatively high absorbed dose to the patient. Recent advances include the digitization of the images captured and flat-panel detector systems which reduce the radiation dose to the patient still further.
Ignorance of the harmful effects of x-rays resulted in the absence of standard radiation safety procedures which are employed today. Scientists and physicians would often place their hands directly in the x-ray beam resulting in radiation burns. Trivial uses for the technology also resulted, including the shoe-fitting fluoroscope used by shoe stores in the 1930s-1950s.
Due to the limited light produced from the fluorescent screens, early radiologists were required to sit in a darkened room, in which the procedure was to be performed, accustomizing their eyes to the dark and thereby increasing their sensitivity to the light. The placement of the radiologist behind the screen resulted in significant radiation doses to the radiologist. 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.
The development of the X-ray image intensifier and the television camera in the 1950s revolutionized fluoroscopy. The red adaptation goggles became obsolete as image intensifiers allowed the light produced by the fluorescent screen to be amplified, allowing it to be seen even in a lighted room. The addition of the camera enabled viewing of the image on a monitor, allowing a radiologist to view the images in a separate room away from the risk of radiation exposure.
More modern improvements in screen phosphors, image intensifiers and even flat panel detectors have allowed for increased image quality while minimizing the radiation dose to the patient. Modern fluoroscopes use CsI screens and produce noise-limited images, ensuring that the minimal radiation dose results while still obtaining images of acceptable quality.
A study has been performed by the Food and Drug Administration (FDA) entitled Radiation-induced Skin Injuries from Fluoroscopy with an additional publication to minimize further fluoroscopy-induced injuries, Public Health Advisory on Avoidance of Serious X-Ray-Induced skin Injuries to Patients During Fluoroscopically-Guided Procedures
While deterministic radiation effects are a possibility, radiation burns are not typical of standard fluoroscopic procedures. Most procedures sufficiently long in length to produce radiation burns are part of necessary life-saving operations.
The invention of X-ray image intensifiers in the 1950s allowed the image on the screen to be visible under normal lighting conditions, as well as providing the option of recording the images with a conventional camera. Subsequent improvements included the coupling of, at first, video cameras and, later, CCD cameras to permit recording of moving images and electronic storage of still images.
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 approximately 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.
Image intensifiers are available with input diameters of up to 45 cm, and a resolution of approximately 2-3 line pairs mm-1.
Flat panel detectors are considerably more expensive to purchase and repair than image intensifiers, so their uptake is primarily in specialties that require high-speed imaging, e.g., vascular imaging and cardiac catheterization.
Another common procedure is the modified barium swallow study during which barium-impregnated liquids and solids are ingested by the patient. A radiologist records and, with a speech pathologist, interprets the resulting images to diagnose oral and pharyngeal swallowing dysfunction. Modified barium swallow studies are also used in studying normal swallow function.