16 Fluoroscopy pt1

Fluoroscopy

Allows imaging of the movement of internal structures; uses a continuous or pulsed x-ray beam; traditional units place the x-ray tube under the table and the image intensifier or digital detector above the patient; image receptor considered a primary barrier; has a deadman type switch and a 5-minute timer; images are viewed on a display monitor.

Image intensification

Provides a method of increasing the brightness of the fluoroscopic image to improve viewing.

Input phosphor

Converts exit radiation (x-rays) into visible light.

Photocathode

Converts visible light from the input phosphor into electrons.

Electrostatic focusing lenses

Accelerate and focus electrons toward the anode/output phosphor.

Output phosphor

Converts high-speed electrons into visible light to produce the intensified image.

CCD camera (charge-coupled device)

Solid-state device that picks up visible light from the output phosphor and converts it into a digital (video) signal.

Viewing system / display monitor

Converts the output phosphor visible light into an electronic (video) signal and displays the fluoroscopic image on the monitor.

Brightness gain

Increase in image brightness due to high-speed electrons striking the output phosphor; calculated as flux gain × minification gain.

Flux gain

The increase in light intensity at the output phosphor due to acceleration (increased energy) of electrons.

Minification gain

The increase in brightness caused by reducing the image size from the input phosphor to the output phosphor.

Brightness conversion factor (CF)

Measures brightness gain as output luminance divided by input exposure rate; units often expressed as cd/m² ÷ mGya/s; a higher CF means a more efficient image intensifier.

Automatic brightness control (ABC)

System that maintains overall image appearance (brightness and contrast) by automatically adjusting kVp, mA, or both; operator selects desired brightness level which ABC maintains.

Magnification mode

Improves visibility of small anatomic structures by increasing voltage to electrostatic focusing lenses so the focal point shifts farther from the output phosphor; using magnification increases patient exposure with image intensifier systems.

Continuous fluoroscopy

Uses a nonstop x-ray beam to create moving images; associated with higher radiation dose.

Pulsed fluoroscopy

Emits x-rays in pulses rather than continuously; reduces patient radiation dose compared with continuous mode.

Deadman type switch

Safety control that must be held to enable x-ray emission; x-rays stop when switch is released.

5-minute timer

Feature that alerts or stops fluoroscopy after 5 minutes to limit radiation exposure.

Image receptor as primary barrier

In traditional fluoroscopy the image receptor (intensifier/detector) is positioned above the patient and acts as a primary protective barrier.

Early fluoroscopy

Original fluoroscopy used direct viewing with image intensifiers before modern digital display monitors and CCD/digital detectors.

Fluoroscopic image quality

Depends on spatial resolution, distortion, brightness, noise, and detector design; often measured in lp/mm (line pairs per millimeter).

Spatial resolution (fluoroscopy)

Measured in line pairs per millimeter (lp/mm).

Pincushion distortion (pincushioning)

Distortion from the image intensifier design that causes edges to appear curved inward or warped.

Vignetting

Peripheral fall-off; loss of brightness at the edges of the image (decreased brightness at the periphery).

Image noise

Grainy appearance that impairs visibility of structures; often due to underexposure.

Quantum noise

Noise caused by insufficient x-ray photons (underexposure); visibility improves by increasing mA (exposure).

Increase exposure to reduce noise

Image noise (quantum noise) can be improved by increasing milliamperage (mA) to increase photon flux.

Flat panel detector fluoroscopy

Modern fluoroscopy that uses digital flat panel detectors; can improve image quality and may reduce patient radiation exposure.

Types of recording devices for fluoroscopy

May include CCD capture, digital frame grabbers, and modern flat panel digital recording systems.

Television camera / electronic devices

Used to convert output phosphor visible light into an electronic video signal for viewing; historically TV cameras, now solid-state digital devices.

Effect of magnification on patient dose

Operating in magnification mode increases patient radiation dose because the system increases exposure to preserve image quality at smaller FOV.

Fluoroscopic safety procedures

Include shielding (lead aprons, thyroid shields), minimizing exposure time, maximizing distance, using pulsed mode, using ABC appropriately, deadman switch use, and 5-minute timer awareness.

Quality control in fluoroscopy

Routine checks and maintenance to ensure consistent image quality, correct radiation output, and safe equipment operation.

Specialized fluoroscopic units

Designed for particular procedures (GI studies, interventional vascular work, orthopedic procedures, etc.) with features tailored to those tasks.

Traditional unit design (summary)

X-ray tube under the table, image intensifier or digital detector above the patient, image receptor acts as a primary barrier, designed for real-time imaging.

Factors that impact image quality and patient exposure

kVp, mA, exposure time (continuous vs pulsed), ABC settings, detector technology (image intensifier vs flat panel), magnification mode, and recording/processing electronics.