Fluoroscopy is a type of medical imaging that shows a continuous X-ray image on a monitor, much like an X-ray movie.
In its primary application of medical imaging, a fluoroscope allows a physician 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.
HOW IT WORKS
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 (such as bone tissue) 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.
Most modern injected radiographic positive contrast media are iodine-based. Iodinated contrast comes in two forms: ionic and non-ionic compounds. Non-ionic contrast is significantly more expensive than ionic (approximately three to five times the cost), however, non-ionic contrast tends to be safer for the patient, causing fewer allergic reactions and uncomfortable side effects such as hot sensations or flushing. Most imaging centers now use non-ionic contrast exclusively, finding that the benefits to patients outweigh the expense.
WHEN ITS USED
Investigations of the gastrointestinal tract, including barium enemas, defecating proctograms, barium meals and barium swallows, and enteroclysis.
Liver biopsy is performed under fluoroscopic guidance at many centers.
Orthopaedic surgery to guide fracture reduction and the placement of metalwork.
Podiatric Surgery to guide fracture reduction and in use in certain procedures that have extensive hardware.
Angiography of the leg, heart and cerebral vessels.
Placement of a PICC (peripherally inserted central catheter)
Placement of a weighted feeding tube (e.g. Dobhoff) into the duodenum after previous attempts without fluoroscopy have failed.
Urological surgery – particularly in retrograde pyelography.
Cardiology for diagnostic angiography, percutaneous coronary interventions, (pacemakers, implantable cardioverter defibrillators and cardiac resynchronization devices)
Discography, an invasive diagnostic procedure for evaluation for intervertebral disc pathology.
RISKS AND BENEFITS
Because the patient must be exposed to a continuous source of X-rays instead of a momentary pulse, a fluoroscopy procedure generally subjects a patient to a higher absorbed dose of radiation than an ordinary (still) radiograph.
Some fluoroscopy procedures may be performed as outpatient procedures while the patient is awake – for example, upper gastrointestinal series to examine the esophagus, stomach and small intestine, or a barium enema to examine the colon.
Other procedures are performed as same-day hospital procedures or sometimes as inpatient procedures, typically while the patient is sedated – for example, cardiac catheterization to examine the heart and the coronary arteries that supply blood to the heart muscle. Still other fluoroscopy procedures may be performed under general anesthesia during surgery – for example to help align and fix fractured bones.
Fluoroscopy can be used to examine the digestive system using a substance which is opaque to X-rays (usually barium sulfate or gastrografin), 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 (positive contrast), which allows the shape of the digestive tract to be outlined as white or clear on an X-ray. Air may then be introduced (negative contrast), which looks black on the film. The barium meal is an example of a contrast agent swallowed to examine the upper digestive tract. Note that while soluble barium compounds are very toxic, the insoluble barium sulfate is non-toxic because its low solubility prevents the body from absorbing it.