X-ray physics notes curriculum
Fundamentals of radiation
The X-ray machine
Production of X-rays
Interaction of radiation with matter
X-ray detection and image formation
Image quality
Radiation safety in X-ray imaging
Fluoroscopy (current module)
Mammography
Fluoroscopy is a real-time X-ray imaging technique that allows continuous or pulsed visualisation of dynamic processes within the body.
It enables observation of motion (such as swallowing, catheter guidance, or contrast flow) rather than static anatomy as in projection radiography.
This articles serves as a basic introduction to fluoroscopy before diving into the topics in more depth.
Purpose of Fluoroscopy
- Provides dynamic imaging of physiological motion and interventional procedures.
- Used in:
- Gastrointestinal studies (barium swallow, enema).
- Orthopaedic theatre screening.
- Interventional radiology (angiography, stenting).
- Cardiology (cardiac catheterisation).
- Urology (nephrostomy, ureteric stent placement).
Fluoroscopy trades temporal resolution (real-time imaging) for higher patient dose compared with a single radiograph.
Basic Principle
A fluoroscopic system continuously exposes the patient to X-rays, producing a stream of photons that pass through the body and strike an image receptor.
The detector converts these photons into a visible image that updates rapidly (typically 7.5–30 frames per second) to create moving images.
X-rays → Detector → Video Signal → Monitor
Modern systems use pulsed exposures rather than continuous beams, significantly reducing dose while maintaining adequate temporal resolution.
Key Components of a Fluoroscopic System
| Component | Function |
|---|---|
| X-ray tube | Generates X-rays, often with continuous heat loading capability (rotating anode, high heat capacity). |
| Image receptor | Converts transmitted X-rays to a visible or digital image. Two main types: image intensifier (II) or flat-panel detector (FPD). |
| Image processing system | Amplifies, digitises, and optimises image brightness and contrast in real time. |
| Display system | High-frame-rate monitor showing live images to the operator. |
| Control system | Includes Automatic Brightness Control (ABC) to maintain constant image brightness despite patient or field changes. |
Modes of Operation
| Mode | Description | Typical Frame Rate | Use |
|---|---|---|---|
| Continuous fluoroscopy | Constant X-ray beam | 25–30 fps | Rare; legacy systems |
| Pulsed fluoroscopy | Short X-ray pulses at discrete intervals | 3–15 fps | Modern standard; large dose reduction |
| Fluoro-store / last-image hold | Displays last frame without continuous exposure | — | Dose-free image review |
| Cine / digital acquisition | High-dose, high-frame-rate capture | 15–30 fps | Angiography and cardiac imaging |
Image Sequence and Real-Time Display (basic summary)
Each frame of a fluoroscopic sequence is created by:
- X-ray pulse emitted by the tube.
- Attenuated beam detected by the receptor (II or FPD).
- Electrical signal converted to a digital image.
- Image displayed on screen within milliseconds.
High frame rates ensure temporal continuity, while automatic exposure control maintains consistent brightness as patient thickness or attenuation changes.
Key Takeaways and Exam Tips:
- Fluoroscopy = real-time X-ray imaging, balancing temporal resolution and dose.
- Two main detector types: image intensifier and flat-panel detector.
- Pulsed fluoroscopy greatly reduces dose vs continuous mode.
- Automatic Brightness Control (ABC) maintains constant image brightness.
- High doses possible during long procedures → continuous dose monitoring essential.
- Common exam question: “Explain the principle of fluoroscopy and outline the components of a modern fluoroscopic system.”
Up Next
Next, we’ll move on to Image Intensifier Systems, explaining how image intensifiers convert X-rays into bright, visible images and how brightness gain is achieved and controlled.