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Fluoroscopy

Continuous X-ray imaging that shows motion in real time: the eye of interventional procedures, but a modality that carries deterministic-effect risk in long cases.

Modality profile· ~10 min read· With photos & sources
Mobile fluoroscopy unit (C-arm with image intensifier)
A mobile fluoroscopy unit (C-arm image intensifier) used in the operating room.  Foto: Wikimedia Commons · CC BY-SA 4.0

Overview

Fluoroscopy delivers X-rays continuously (or in pulses) to show what is happening inside the body as a real-time, moving image. This makes it indispensable for procedures that need guidance, such as interventional radiology and cardiology (angiography, stents, catheters), gastrointestinal barium studies and orthopedic surgery.1

How it works

In classic systems, the beam passing through the patient reaches an image intensifier; this tube converts X-rays into bright visible light, producing a viewable image even at low beam intensity. In modern units, the image intensifier has largely been replaced by flat-panel detectors. The tube and detector usually face each other on a C-arm that can be rotated to different angles around the patient.1

Continuous vs pulsed fluoroscopy

One of the most important dose-reduction approaches is pulsed fluoroscopy: instead of a continuous beam, X-rays are delivered as a set number of short pulses per second. A change such as switching from continuous fluoroscopy to 15 pulses per second can save dose; the literature reports about a 22% dose saving for this switch.2 In addition, techniques such as last-image hold, collimation, grid removal, beam filtration and adjusting distance to the patient/detector reduce dose.2

Dose and deterministic effects

Fluoroscopy's distinctive risk is the high dose that can accumulate in the skin during long interventional procedures. After interventional use expanded in the 1980s, radiation-induced skin injuries became a concern by around 1990; the most likely cause was seen to be multiple and long procedures performed at normal dose rates.3 Such deterministic injuries (skin damage, hair loss, cataract) occur only when the dose to the tissue exceeds a threshold.3

The key difference
In most diagnostic exams the main concern is stochastic (probabilistic) risk; in fluoroscopy, long procedures can also raise deterministic skin effects if the threshold is exceeded. That is why dose monitoring and reduction techniques are especially critical here.

Our detailed article on the distinction between deterministic and stochastic effects and the threshold concept: Fundamentals of Radiation Protection.

Image type
Real-time moving
Detector
Image intensifier / flat panel
Dose reduction
Pulsed mode, collimation, distance
Special risk
Deterministic skin effect (long cases)

References

  1. U.S. FDA. Fluoroscopy (principles, image intensifier/flat panel, clinical uses). fda.gov · Fluoroscopy
  2. Mahesh M. Fluoroscopy: Patient Radiation Exposure Issues. RadioGraphics 2001 (pulsed fluoroscopy and dose-reduction techniques). pubs.rsna.org
  3. Wagner LK, Archer BR, et al. (review of fluoroscopic skin injury and deterministic thresholds). See also ICRP Publication 118, Statement on Tissue Reactions. icrp.org · Publication 118
  4. Image: File:Mobile X-ray image intensifier.JPG, Wikimedia Commons, CC BY-SA 4.0.
Note: Dose rates and thresholds vary by procedure, device and technique. For interventional dose management, consult a qualified medical physicist and current guidelines.

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