Fluoroscopy

Image:Fluoroscope.jpg

Fluoroscopy is an imaging technique commonly used by physiciansto obtain real-time images of the internal structures of a patient through the use of a fluoroscope. In its simplest form, a fluoroscope consists of an x-raysource and fluorescent screen between which a patient is placed. However, modern fluoroscopes couple the screen to an x-ray image intensifierand CCDvideo cameraallowing 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 doserates during fluorscopy procedures, the length of a typical procedure often results in a relatively high absorbed doseto 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.

History

The beginning of fluoroscopy can be traced back to 8 November1895when Wilhelm Röntgennoticed a bariumplatinocyanidescreen fluorescing as a result of being exposed to what he would later call x rays. Within months of this discovery, the first fluoroscopes were created. Thomas Edisonquickly discovered that calcium tungstatescreens produced brighter images and is credited with designing and producing the first commercially available fluoroscope. In its infancy, many incorrectly predicted that the moving images from fluoroscopy would completely replace the still x-ray radiographs, but the superior diagnostic quality of the earlier radiographs prevented this from occurring.

Ignorance of the harmful effects of x raysresulted 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.[1]

Due to the limited light produced from the fluorescent screens, early radiologistswere 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 dosesto the radiologist. Red adaptation goggleswere developed by Wilhelm Trendleenburgin 1916to address the problem of dark adaptationof 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 image intensifierand the television camerain the 1950srevolutionized fluoroscopy. The red adaptation gogglesbecame 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 cameraenabled 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 detectorshave allowed for increased image quality while minimizing the radiation dose to the patient. Modern fluoroscopes use CsIscreens and produce noise-limited images, ensuring that the minimal radiation dose results while still obtaining images of acceptable quality.

Risks

Because fluoroscopy involves the use of x rays, a form of ionizing radiation, all fluoroscopic procedures pose a potential health risk to the patient. Radiation doses to the patient depend greatly on the size of the patient as well as length of the procedure, with typical skin dose rates quoted as 20-50 mGy/min. Exposure times vary depending on the procedure being performed but procedure times up to 75 minutes have been documented. Because of the long length of some procedures, in addition to standard cancer-inducing stochastic radiation effects, deterministic radiation effects have also been observed ranging from mild erythema, equivalent of a sun burn, to more serious burns.

A study has been performed by the FDAentitled Radiation-induced Skin Injuries from Fluoroscopy[2]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 Fluroscopically-Guided Procedures[3].

While deterministic radiation effects are a possible, radiation burnsare not typical of standard fluoroscopic procedures. Most procedures sufficiently long in length to produce radiation burns are part of necessary life-saving operations.

Fluoroscope design

The first fluoroscopes consisted of an x-ray source and fluorescent screen between which the patient would be placed. As the x rays pass through the patient, they are attenuatedby varying amounts as they interact with the different internal structures of the body, casting a shadowof the structures on the fluorescent screen. Images on the screen are produced as the unattenuated x rays interact with atoms in the screen through the photoelectric effect, giving their energy to the electrons. While much of the energy given to the electronsis dissipated as heat, a fraction of it is given off as visible light, producing the images. Early radiologistswould adapt their eyes to view the dim fluoroscopic images by sitting in darkened rooms, or by wearing red adaptation goggles.

The invention of image intensifiersin the 1950sallowed the light from the screen to be amplified, removing the need for radiologists to adapt their eyes. The image intensifiers make use of photomultiplier tubes, increasing a single input lightphotoninto as many as 10⁸ output photons, greatly increasing the brightness of the output images.

By coupling the image intensifier to a CCD camera, the output image can be recorded and displayed on a monitor, allowing the radiologist to view them in a separate room, away from the risk of radiation exposure.

Advances in screen designs have allowed for increased image quality and lower dose rates to patients. Increases in the quantum efficiencyof phosphorsused results in more incoming x rays being converted into visible light allowing the number of x rays, and therefore the radiation dose, to be reduced.

The introduction of flat-panel detectors allows for the replacement of the image intensifier in fluoroscope design. Increased sensitivity to x rays allow for lower radiation doses, while removing blurring introduced into the system by the image intensifier.

Imaging concerns

In addition to spatial blurring factors that plague all x-ray imaging devices, caused by such things as Lubberts effect, K-fluorescencereabsorption and electronrange, fluoroscopic systems also experience temporal blurring due to system lag. This temporal blurring has the effect of averaging frames together. While this helps reduce noise in images with stationary objects, it creates motion blurringfor moving objects. Temporal blurring also complicates measurements of system performancefor fluoroscopic systems.

Common procedures involving the use of fluoroscopy

• Investigations of the gastrointestinal tract, including Barium enemas, barium mealsand barium swallows, and enteroclysis.
• Orthopaedic surgeryto guide fracture reduction and the placement of metalwork.
• Angiographyof the leg, heart and cerebral vessels.
• Urological surgery– particularly in retrograde pyelography.

See also

• Absorbed dose
• Image intensifier
• Ionizing radiation
• Medical Imaging
• X Ray
• Radiology
• Radiography

External links

• "Were those old shoe store fluoroscopes a health hazard?" at Straight Dope, 27 November1987

• - Fluoroscopy Equipment and Information from Siemens Medicalru:????????????

This article is licensed under the GNU Free Documentation License.
It uses material from the http://en.wikipedia.org/wiki/Fluoroscopy Wikipedia article Fluoroscopy.