Fluoroscopy


Fluoroscopy, informally referred to as "fluoro", is an imaging technique that uses X-rays 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 structure and function 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 source and a fluorescent screen, between which a patient is placed. However, since the 1950s most fluoroscopes have included X-ray image intensifiers and cameras 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 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.

Mechanism of action

Although visible light can be seen by the naked eye, it does not penetrate most objects. In contrast, X-rays can penetrate a wider variety of objects, but they are invisible to the naked eye. To take advantage of the penetration for image-forming purposes, one must somehow convert the X-rays' intensity variations into a form that is visible. Classic film-based radiography achieves this by the variable chemical changes that the X-rays induce in the film, and classic fluoroscopy achieves it by fluorescence, in which certain materials convert X-ray energy into visible light. This use of fluorescent materials to make a viewing scope is how fluoroscopy got its name.
As the X-rays pass through the patient, they are attenuated by varying amounts as they pass through or reflect off the different tissues of the body, casting an X-ray shadow of the radiopaque tissues on the fluorescent screen. Images on the screen are produced as the unattenuated or mildly attenuated X-rays from radiolucent tissues interact with atoms in the screen through the photoelectric effect, giving their energy to the electrons. 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 bright enough to see without goggles under normal ambient light. Image Intensifiers are still being used to this day with many new models still using II 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.
Nowadays, in all forms of digital X-ray imaging 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 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.

Medical use

Fluoroscopy has become an important tool in medical imaging to render moving pictures during a surgery or any other procedure.

Surgical fluoroscopy

Fluoroscopy is used in various types of surgical procedure, such as orthopaedic surgery and podiatric surgery.
In both of those, it is used to guide fracture reduction and in use in certain procedures that have extensive hardware. Specifically, once the fracture is realigned, a surgeon will drill a guide pin into the bone tissue and use fluoroscopy to insure proper angle of the pin - then a cannulated drill bit is inserted over the pin to prepare a ‘hole’ for a bone screw. If the surgeon prefers a different angle, they simply reverse the pin and redrill. Fluoroscopy will be use for each screw placed -which has greatly improved proper fracture heal due to more accurate reduction.

Urology

In urology, fluoroscopy is used in retrograde pyelography and micturating cystourethrography to detect various abnormalities related to the urinary system.
Fluoroscopy is used to confirm needle and guide wire location when placing a nephrostomy. It is also increasingly employed during percutaneous nephrolithotomy, where low-dose pulsed fluoroscopy techniques have been shown to significantly reduce radiation exposure for both patients and surgical staff without compromising procedural outcomes.

Cardiology

In cardiology, fluoroscopy is used for diagnostic angiography, percutaneous coronary interventions,.

Gastrointestinal fluoroscopy

Fluoroscopy can be used to examine the digestive system using a substance that is opaque to X-rays, which is introduced into the digestive system either by swallowing or as an enema. This is normally as part of a double-contrast technique, using positive and negative contrast. Barium sulfate coats the walls of the digestive tract, which allows the shape of the digestive tract to be outlined as white or clear on an X-ray. Air may then be introduced, which looks black on the film. The barium meal is an example of a contrast agent swallowed to examine the upper digestive tract. While soluble barium compounds are very toxic, the insoluble barium sulfate is nontoxic because its low solubility prevents the body from absorbing it. Investigations of the gastrointestinal tract include barium enemas, defecating proctograms, barium meals and swallows, and enteroclysis.

Other medical uses

Fluoroscopy is also used in airport security scanners to check for hidden weapons or bombs. These machines use lower doses of radiation than medical fluoroscopy. The reason for higher doses in medical applications is that they are more demanding about tissue contrast, and for the same reason they sometimes require contrast media.

History

Early era

Fluoroscopy's origins and radiography's origins can both be traced back to 8 November 1895, when Wilhelm Röntgen, or in English script Roentgen, noticed a barium platinocyanide screen fluorescing as a result of being exposed to what he would later call X-rays. Within months of this discovery, the first crude fluoroscopes were created. These experimental fluoroscopes were simply thin cardboard screens that had been coated on the inside with a layer of fluorescent metal salt, attached to a funnel-shaped cardboard eyeshade which excluded room light with a viewing eyepiece which the user held up to his eye. The fluoroscopic image obtained in this way was quite faint. Even when finally improved and commercially introduced for diagnostic imaging, the limited light produced from the fluorescent screens of the earliest commercial scopes necessitated that a radiologist sit for a period in the darkened room where the imaging procedure was to be performed, to first accustom his eyes to increase their sensitivity to perceive the faint image. The placement of the radiologist behind the screen also resulted in significant dosing of the radiologist.
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.
During this infant commercial development, many incorrectly predicted that the moving images of fluoroscopy would completely replace roentgenographs, 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.
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.