Fluoroscopic Imaging Fundamentals

Fluoroscopic Imaging

• Fluoroscopy is a type of medical imaging that shows a continuous X-ray image on a monitor, similar to an X-ray movie.

Applications of Fluoroscopy

• Orthopaedic: Arthrograms, theatre procedures
• Angiography: Cardiac, cerebral, peripheral
• GI Tract: Barium swallows, meals, and enemas
• Endoscopy: ERCP, OGD
• Urology: Ureteroscopy, nephrostomy insertions, PCNL
• Interventional Radiology: Line insertions, Embolisations, PTC

Fixed Systems

• Installed in a specific room or suite
• Typically used for longer screening cases
• Variety of styles: floor mounted, ceiling mounted, biplane

Mobile Systems

• Portable
• Used to support theatre cases and shorter or less complex interventions
• Can be moved between theatres

Comparison of System Advantages

• Mobile Systems: Does not require custom room design, can be moved between theatres, often better radiation protection
• Fixed Systems: More reliable x-ray generators, often more features, room is designed to allow uninhibited movement of c-arm

X-ray Generation

• Mechanism similar to conventional x-ray systems
• Modes: Continuous fluoroscopy, Pulsed fluoroscopy, High-Dose “Acquisitions”, Single high-dose image

Anode Heat Dissipation

• High-speed rotational anodes
• Oil or water cooled systems
• Range of focal spot sizes to balance detail with anode heating depending on application

Image Intensifier

• X-rays pass through the patient and reach the input phosphor
• Input phosphor emits light, which reaches the photoemissive layer, emitting electrons towards the anode
• Electrons reach the output phosphor, producing an amplified light signal
• Light signal is recorded by a camera

Flat Panel Detectors (FPDs)

• Similar to plain film direct digital receptors
• Input x-rays converted into electric via a Selenium photoconductor
• Charge transmitted to a thin-film transistor (TFT) array
• Array arranged in a matrix with each transistor mapped to a pixel

Comparison of Image Intensifier and Flat Panel Detectors

• Advantages of FPDs: Lower dose, greater field of view, higher image quality
• Disadvantages of FPDs: Higher initial cost, size of receptor can impact maneuverability

Contrast Media

• Positive Media: Radiopaque, higher atomic number, attenuates more x-rays, appears “Hyperdense” on image
• Negative Media: Radiolucent, lower atomic number, attenuates less x-rays, appears “Hypodense” on image

Double-Contrast Imaging

• Uses both positive and negative contrast together
• Can be used in Barium meal and Barium Enema investigations

Digital Subtraction Angiography (DSA)

• Process used in angiography to remove distracting detail and anatomical structures from the image
• Operator acquires images before injecting contrast, and computer system creates a “mask” demonstrating the background anatomy
• Subsequent images are subtracted from the mask, leaving only the new information visible on the screen

Biplane Systems

• Digital fluoroscopy systems with multiple c-arms
• Allow simultaneous images in multiple planes

Radiation Protection

• Room designated as a “Controlled Area”
• Warning signs, local radiation rules, and workers wear lead PPE
• Methods to reduce dose: Low dose fluoroscopy setting, collimation, reduce exposure factors, reduce SID, staff stand further from primary beam, reduce pulse/frame rate, use shallow angles, lead shielding, staging the procedure

Exposure Factor Control

• Automatic Brightness Control (ABC): Adjusts kVp and mAs to maintain a present brightness level
• Automatic Dose Rate Control (ADRC): Algorithmically controls exposure factors based on anatomical thickness and applies initial setting based on the program selected

Image Quality – Further Considerations

• Screen position, cleanliness of screens, lighting of the room, display settings
• Collimation: Reduces irradiation of unnecessary anatomy, reduces scatter, and affects the full circumference of the image
• Filtration: Reduces skin dose, reduces “flare” on the image, improves visibility
• Exposure Lock: Locks the exposure at a previously used level or overrides and sets manual parameters to prevent unnecessary compensation for high-density objects