Fluoroscopy

Fluoroscopy is a technique that employs x-rays to generate real-time still images or video of a patient's body. The x-rays pass through the body and create an image on a detector, which is then transmitted to a monitor for viewing by the physician. Thus, a part of the body that is radio-opaque or made so by the use of a dye or a contrast agent can be visualized. Similarly, an instrument or device or movement of internal body parts can be displayed.[1, 2, 3]

It is a commonly used medical technique that helps physicians with a wide variety of diagnostic and interventional procedures. Although low doses are used, in prolonged procedures, the cumulative exposure may result in a relatively high absorbed dose to the patient. Therefore, all necessary precautions should be used, and the benefits should outweigh the potential risks in a given clinical situation.[4, 5, 6, 7, 8]

Because fluoroscopy involves the use of ionizing radiation, it is relatively contraindicated in pregnant women because of potentially harmful effects on a developing fetus.

This review focuses on the use of fluoroscopy in orthopedic procedures.

Fluoroscopy is used in many types of examinations and procedures. Some examples include the following:

• Orthopedic procedures, such as manipulation of broken bones in fracture reduction or insertion of implants and checking appropriate positioning or alignment.

• Gastrointestinal investigations using contrast agents, such as barium in the intestine to study its outline and movement.

• Cardiovascular and interventional radiology procedures, such as catheter insertion and monitoring of its progress (eg, to undo a blockage or insert a stent).

 

A fluoroscope in its simplest form (although rarely, if ever, used now) is an x-ray source at one end and a fluorescent screen at the other end. The part of the body that is to be imaged is placed between these ends. Low-dose radiation is used, and modern fluoroscopes couple the screen to an x-ray image intensifier to brighten the image sufficiently so as to be displayed as still images or video on a monitor. Recent advances allowing digitalization of the images and the use of flat panel detector systems have helped to further decrease the dose of radiation used.

Current equipment and safety measures help reduce the risks associated with fluoroscopy, including the following:

• Display of the duration, rate, and cumulative amount of radiation exposure patients receive.[1]

• Increased x-ray filtration to reduce the possibility of radiation injuries during long procedures.

• Tighter controls on the size of the x-ray field to reduce the amount of radiation that falls outside the image target area.

• A last-image-hold feature that allows the physician to view images without continually exposing patients to radiation.

• Use of a laser localization attachment to the C-arm helps position the x-ray source precisely over the area under scrutiny and minimizes repeat exposures due to imprecise positioning

Fluoroscopy involves the use of ionizing radiation and, therefore, carries the same types of risk as other x-ray procedures. The radiation dose a patient receives depends on a variety of factors, including the body part examined and the duration of the procedure.[9, 10, 11] The exposure and dose required in an obese patient is greater than in a lean patient, and abdominal fluoroscopy results in a greater exposure than fluoroscopy of the hand or wrist because of the increased thickness and tissue density of the abdomen.[4]

Two types of risks are associated with fluoroscopy (and other ionizing radiation exposures):

• Deterministic risks: The risk is nonexistent below a certain threshold of radiation dose, but it is nearly 100% at dose levels significantly greater than this threshold (eg, radiation burns to the skin and radiation-induced cataracts).

• Stochastic risks: The risk is directly proportional to the radiation dose, with no minimum dose below which the risk is zero (eg, radiation-induced cancer).

In practice, a risk of radiation burns exists only when fluoroscopy is conducted over prolonged periods of time and with the use of higher doses of radiation. Regarding stochastic risks, the "as low as reasonably achievable" (ALARA) principle applies in that the radiation dose should be made as small as reasonably achievable to reduce these risks to an absolute minimum. When a medical need exists, however, the benefit of fluoroscopy usually far exceeds the small but real cancer risk associated with the procedure. Therefore, fluoroscopy is used with the lowest possible exposure for the shortest possible time.

Two main types of fluoroscopic equipment are used: fixed and mobile. A fixed or permanently installed fluoroscopic system typically uses a radiolucent patient examination table with an undertable-mounted tube and an imaging detector mounted over the table. Fixed systems are used in designated rooms for studies such as barium studies, catheterization of blood vessels, and endoscopy of the gastrointestinal tract.

A C-arm is typically a mobile fluoroscopic unit with the x-ray source at one end and the image detector at the other end. The C-arm unit allows for greater operator flexibility, and the equipment can be moved to wherever the fluoroscopic examination is needed. A C-arm is commonly used in operating rooms where orthopedic procedures are performed to visualize bones or implants.

Reduction of risks due to ionizing radiation can be achieved by various measures, which involve the design and usage of equipment, use of targeting devices, and certain measures that can be taken by the personnel involved.[5]

In vertical positioning, the x-ray source is under the table, and the image intensifier is above (see the images below). This positioning is preferable because it reduces scatter radiation, because even the scattered x-rays must pass through the patient before they reach medical personnel in the patient's vicinity. Therefore, exposure due to scatter x-rays is less. The patient should be positioned as far from the x-ray source as practicable to minimize patient skin entrance dose. The image intensifier should be positioned as close to the patient as practicable. This results in a lower patient dose and a sharper image.

Scatter is great in horizontal positioning for cross-table fluoroscopy and in vertical positioning in which the tube is above the table and the part to be screened is closer to the image intensifier (see the image below). Such positioning should be avoided if possible.

Lead Shielding

Protection of the patient and other personnel in the vicinity during the conduct of fluoroscopy is an important safety requirement. Lead aprons, lead gloves, lead neck or thyroid shields, lead eyeglasses, lead drapes, and lead glass barriers help reduce the radiation exposure to the personnel. A lead barrier of 0.25-mm lead equivalent thickness typically stops 90% of the x- rays, and a 0.5-mm lead equivalent apron typically absorbs 97% of x-rays.

Safety regulations require that all persons, including staff or other patients, within 2 meters of the tube head, direct beam, or exposed area of the patient’s body be protected by lead shielding of a thickness equivalent to 0.25 mm of lead (Pb). Furthermore, gonadal lead shielding of at least 0.5 mm Pb-equivalent shielding must be used for patients who have not passed reproductive age for radiographic procedures. Since staff aprons are frequently used for this function, current recommendations state that all lead or lead-equivalent aprons be of 0.5 mm Pb-equivalence.

Distance

Radiation dose rate varies inversely to the square of the distance from the source. The main source of radiation exposure to medical personnel is from scattered radiation from the patient, not from the x-ray tube. In the interest of radiation safety, all persons, including staff or other patients, must be as far as possible (at least 2 meters) from the tube head, direct beam, or exposed area of the patient’s body unless protected by lead barriers.

Targeting

The use of a laser-aiming device to help position during fluoroscopy is recommended in an effort to reduce radiation exposure.

Panchbhavi et al reported a prospective study on whether the use of a laser-aiming device attached to the C-arm improves the accuracy of intraoperative fluoroscopy, in order to reduce, by implication, radiation exposure in the operating room.[2]  The study included 92 consecutive cases requiring use of fluoroscopy for foot and ankle surgery. The number of accurate and inaccurate images with or without the presence of a radiology technician and a laser-aiming device were compared. They found that the accuracy of imaging with the laser-aiming device was higher than the imaging without the device (P<.001). The accuracy of the images obtained by the surgeon was higher than the technicians’ images when laser guidance was used (P =.027). There was no significant difference between the images obtained by the surgeon or the technicians when the aiming device was not used (P =.09).