Fluoroscopy

Fluoroscopy Definition

Fluoroscopy is a diagnostic imaging technique that employs X-rays for obtaining real-time moving imagery of the internal structure of a patient through the use of a fluoroscope.

How is Fluoroscopy Done?

A Fluoroscope generally comprises of a fluorescent screen and an X-ray source. The patient is placed between the source and the screen. Modern fluoroscopes attach an additional X-ray image intensifier as well as a CCD video camera which allow recording of the images and playing them on a monitor.

Picture of Fluoroscopy

Picture 1 – Fluoroscopy

While using X-rays, actually a type of ionizing radiation, care should be taken so as to balance the risks of the procedure with the benefits that it can bring to the patient. Although physicians always attempt to use low dosage of X-rays during fluoroscopic procedures, generally the overall length of a procedure exposes the patient to a relatively high dose. More recent advances allow digitization of images, a process known as digital fluoroscopy that allow capturing of images and have introduced flat panel detector systems which reduce the dosage of X-rays.

Biplane Fluoroscopy

This method allows a diagnostician to take X-ray images in both horizontal as well as in vertical planes.

History of Fluoroscopy

The origin of fluoroscopy goes back to Wilhelm Röntgen. On 8th November, 1895, he noticed a fluorescing effect on a screen of a barium platinocyanide due to exposure to X-rays. The initial fluoroscopes were created within a few months of this initial discovery. The earliest fluoroscopes were made out of cardboard funnels that were open at the narrow end for observation, and the wider end was enclosed with a piece of thin cardboard coated inside with a fluorescent metal salt layer. The fluoroscopic images that were acquired in this way were rather faint. It was then iconic inventor Thomas Edison discovered that screens made of calcium tungstate produced brighter and clearer images; he was credited with conceptualizing the first commercially-available fluoroscopes.

No standard radiation safety measures were practiced during the earlier days, as the ill effects of X-rays were unknown during that time. Physicians and scientists often unknowingly exposed themselves directly to X-ray beams which resulted in radiation burns.

As the earlier fluorescent screens produced limited light, the earlier radiologists were needed to be in a dark room where they used to adjust their vision to the darkness and increase their light sensitivity. The radiologist was also exposed to significant amounts of radiation as he used to sit behind the screen. The problem of adjusting vision to darkness was solved when Wilhelm Trendelenburg developed red adaptation goggles in the year 1916.

The practice of fluoroscopy was revolutionized when Westinghouse developed X-ray image intensifier during the late 1940s and also when close circuit television cameras were introduced around a decade later. Image intensifiers could amplify the light emanated from the fluorescent screen which made the images visible even in lighted rooms. This made the red adaptation goggles obsolete. The camera allowed viewing the images remotely in a monitor and negated the risk of exposure to radiation.

The latest developments in image intensifiers, screen phosphors and flat panel detectors have enabled physicians to obtain more high quality images and have minimized the chances of the patient being exposed to harmful radiation. The modern fluoroscopy machines employ CSI screens and generate noise-limited images, making sure that minimum amount of radiation produce optimum quality of images.

Fluoroscopy Procedures

Fluoroscopy is widely used in different types of intraoperative procedures and examinations, such as

  • Biopsies
  • Barium X-rays
  • Lumbar puncture
  • Hysterosalpingogram
  • Cardiac catheterization
  • Intravenous pyelogram
  • Hip injection fluoroscopy
  • Percutaneous vertebroplasty
  • Arthrography or visualization of joints
  • Placement of IV or intravenous catheters

Apart from the above mentioned procedures, fluoroscopy is also used in:

  • Gastrointestinal tract investigations, including defecating proctograms, barium enemas, barium swallows, barium meals and enteroclysis
  • Angiography of the chest, heart, leg and cerebral vessels
  • Orthopedic surgeries for the placement of metalwork and reduction of fractures
  • Placement of a peripherally inserted central catheter or PICC
  • Placement of weighted feeding tube like Dobhoff into the duodenum
  • Urological surgery, especially in retrograde pyelography
  • Implantation of cardiac rhythm managing devices, such as pacemakers, cardiac resynchronization devices and implantable cardioverter defibrillators
  • Discography, a diagnostic procedure conducted for evaluating intervertebral disc pathology

Fluoroscopy Equipment

The earliest fluoroscopes had a fluorescent screen and an x-ray source between which a patient was placed. The x-rays are attenuated by different degrees as they come into contact with the internal structures of the body, thereby creating their shadow on the screen. The images are produced on the screen as unattenuated x-rays interact with the atoms present in the screen by photoelectric effect and give their energy to electrons. Although most of the energy supplied to electrons escapes as heat, a small fraction is given off as detectable light – which produces the images.

X-ray image intensifiers

X-ray image intensifiers allow viewing the images that are projected on the screen under normal lighting circumstances and provide the opportunity to record the images using a conventional camera. Later, image intensifiers were coupled with video cameras and CCD cameras that could record moving images and electronically store the still images.

A separate fluorescent screen is not used with the modern-day image intensifiers. Instead, traces of caesium iodide phosphor deposited on photocathode of intensifier tube allows for clearer images. Generally, the output image is almost 105 times brighter than input image. The brightness gain has a flux gain and a minification gain, both of which are approximately 100. Image intensifiers having input diameters up to 45 centimeters and resolution of 2 to 3 line pairs per millimeter are available.

Flat-panel detectors

Flat-panel detectors replaced image intensifiers in a fluoroscope design due to their high sensitivity to X-rays and the ability to reduce the exposure of a patient to radiation. They also produce better temporal resolution than image intensifiers and reduce motion blurring. Such detectors also have a better contrast ratio than image intensifiers. The spatial resolution is more or less equal. However, an image intensifier may provide slightly better results than that of a flat panel when is used in the ‘magnification’ mode.

As flat-panel detectors are generally much more expensive to purchase or repair than standard image intensifiers, they are mostly used in areas which necessitates high-speed imaging, such as cardiac catheterization and vascular imaging.

Contrast Agents

Various substances have been employed as positive contrast agents, such as:

  • Silver
  • Caesium
  • Bismuth
  • Tin
  • Thorium
  • Tungsten
  • Tantalum
  • Lanthanide
  • Zirconium

Thoria or thorium dioxide is not used anymore as an agent as it causes liver cancer. Most of the injected positive contrast agents that are used nowadays are iodine-based. Among the two types of iodine contrasts, ionic and non-ionic, the non-ionic variety tends to be safer for patients and so is used most frequently even though it is more expensive.

Negative radiographic contrast agents include carbon dioxide and air. Carbon dioxide can be naturally absorbed by an individual’s body or can be injected artificially into the blood.

Fluoroscopy Imaging Concerns

Apart from the problem of spatial burning that occurs in all X-ray devices and is caused by Lubberts effect, K-fluorescence re-absorption and electron range, temporal blurring is also seen in fluoroscopic systems as a result of system lag. Temporal blurring causes averaging of the frames together. Although this leads to reduction of noise in producing images with the stationery objects, it causes motion blurring for the moving objects. The occurrence of temporal blurring also makes it difficult to measure system performance for the fluoroscopic systems.

Steps involved in Fluoroscopy

There are some guidelines and steps that a patient needs to be aware of if he or she is going to undergo a fluoroscopic procedure:

Image of Fluoroscopy

Picture 2 – Fluoroscopy Image

Before the procedure

  • The doctor is going to explain the entire procedure to the patient and give scope to ask any questions that he or she may have.
  • The patient will then be asked to approve a consent form which legally allows the doctor(s) to perform a fluoroscopic examination. A patient should go through the form carefully and verify things with the doctor in case anything is not clear.
  • The type of examination or procedure that is being done is going to determine if any preparation is required by the patient prior to that procedure. The doctor in charge will notify the patient of any pre-procedure instructions.
  • The patient should inform the doctor about any possible allergy to iodine or of any bad reaction that he or she might have had before due to the use of any particular contrast dye.
  • A woman who is about to go through a fluoroscopic procedure should inform the doctor if she is pregnant.
  • Patients may also be requested to follow other special preparations that are specific to their case.

During the procedure

  • During fluoroscopy, the doctor will first ask the patient to remove all clothing or jewelry pieces that may hinder proper exposure of a body area that is to be examined.
  • If the patient is asked to remove his or her clothing, a gown will be provided to the patient to wear.
  • A contrast substance might be administered, depending on the procedure type, either by swallowing, by an enema or intravenously through the hand or arm.
  • The patient will then be placed on the fluoroscopy table. Depending on the procedure, the patient might be asked to take different positions, or move a particular body part or control breathing when fluoroscopy is conducted.
  • In procedures such as catheter placement in a joint or in any other body part or in cardiac catheterization, an additional site of line insertion may be used around elbow, groin or some other site.
  • The doctor is going to use an X-ray scanner for producing fluoroscopic images of the area that is being treated or examined.
  • A contrast agent or a dye can also be injected into IV line which can help in better visualization of the structures or organs that is being studied.
  • While conducting arthrography, any joint fluid present might be removed with a needle before the contrast substance is injected in the area. After injection of the contract substance, the patient might be asked to briskly move the joint for some time so that the contrast substance is evenly distributed throughout the joint.
  • The length of a particular fluoroscopic procedure will depend on the type of procedure and the area of the body that is being examined.
  • The doctor will remove the IV line after the procedure is complete.
  • Although fluoroscopy does not cause any pain itself, a particular procedure that is being performed might be painful, such as arthrographic procedures or accessing a vein/artery for angiography. In such cases, doctors might use local anesthesia, general anesthesia or conscious sedation, which may vary with a particular procedure.

After the procedure

The type of fluoroscopic examination that is being performed will determine the care required after the procedure. Procedures like cardiac catheterization will need a recovery period consisting of several hours of rest with total immobilization of the arm or leg where the catheter was inserted; some other procedures might require less recovery time. The patient should notify the doctor if he or she observes any redness, pain or swelling around the IV site after the procedure. This is due to the fact that such signs could denote an infection or some other form of reaction.

Fluoroscopy Risks

As fluoroscopy uses X-rays which is a type of ionizing radiation, fluoroscopic procedures can be potentially health damaging for the patients. The dosage of radiation administered to the patient depends greatly on the overall size of patient as well as the length of a particular procedure, with the typical skin dosage rates being quoted as 20 mGy/min to 50 mGy/min. The duration of exposure varies depending on a particular procedure that is being performed; a procedure can even run as long as 75 minutes. Some procedures which require a longer duration of radiation exposure have been known to cause adverse radiation effects. These may range from being the standard cancer-causing stochastic radiation effects to the deterministic radiation effects that can range from mild erythema to the more serious burns.

Although there is a possibility that a patient might suffer from the effects of deterministic radiation, radiation burns are not commonly atypical of the standard fluoroscopic procedures. Most of the procedures that are sufficiently long in causing radiation burns make up a vital part of life-saving operations.

X-ray image intensifiers normally have radiation-reducing systems, for example, pulsed radiation in pulsed fluoroscopy instead of constant radiation as well as last image hold that help in freezing the screen and extracting the image for further examination without exposing a patient to further radiation.

 

Fluoroscopy has become an indispensable diagnostic tool for various ailments in recent times. The latest technological developments in the medical world further aim at reducing the ill effects of this procedure by minimizing the radiation while capitalizing on its positive results.

References:

http://www.aaos.org/news/aaosnow/dec08/clinical1.asp

https://www.ohsu.edu/xd/health/health-information/topic-by-id.cfm?ContentTypeId=92&ContentId=P07662

http://en.wikipedia.org/wiki/Fluoroscopy

http://www.fda.gov/radiation-emittingproducts/radiationemittingproductsandprocedures/medicalimaging/medicalx-rays/ucm115354.htm

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