Study Notes for Fluoroscopy - Chapter 25

Fluoroscope inventor

Thomas A. Edison

Year the fluoroscope was invented

1896

Primary function of fluoroscopy

To provide dynamic viewing of anatomical structures in real-time.

Vision receptors for low light conditions

Rods (scotopic vision)

Vision receptors for bright light and color perception

Cones (photopic vision)

Light condition associated with scotopic vision

Low light conditions

Light condition associated with photopic vision

Bright light conditions

Unit used to measure illumination

Lux (lumen/square meter)

Typical illumination levels for fluoroscopy

100 to 1000 lux

Component that converts the x-ray beam to a high-intensity visible light image

Image-Intensifier Tube

Image intensifier component that converts x-ray energy to visible light

Input phosphor

Material composing the Input Phosphor

Cesium iodide (CsI)

Image intensifier component that converts visible light to electrons

Photocathode

What is photoemission?

The emission of electrons when illuminated by light (occurs at the photocathode).

Image intensifier component that produces amplified visible light

Output phosphor

Formula for Brightness Gain

Brightness Gain = Minification Gain x Flux Gain

Formula for Minification Gain

Minification Gain = (Diameter of input phosphor / Diameter of output phosphor)^2

Formula for Flux Gain

Flux Gain = Number of output light photons / Number of input x-ray photons

Minification Gain accounts for...

The acceleration and focusing of the electron image from a large input diameter to a smaller output diameter.

Flux Gain accounts for...

The gain in brightness resulting from the conversion efficiency of the output phosphor and the acceleration of electrons.

Fluoroscopic tube operation uses what level of mA?

Lower mA (relative to diagnostic radiography)

Visual acuity definition

The ability to perceive fine detail.

Vision related to detailed viewing and color

Photopic vision (cones)

Typical material composing the Output Phosphor

Zinc cadmium sulfide

What does a camera tube (vidicon) do?

Converts visible light images from the output phosphor into electrical signals.

Common camera tube used in older fluoroscopy systems

Vidicon

What is Automatic Brightness Control (ABC)?

A system that automatically adjusts exposure factors (kVp or mA) to maintain consistent image brightness.

What key safety measure needs monitoring in quality control?

Entrance Skin Dose (ESD)

Recording method allowing for higher quality static images with less interruption

Spot films or photospot cameras

A type of contrast study often using fluoroscopy to examine vessels

Angiography

The transition from rod to cone vision affects image interpretation, particularly in what conditions?

Dim conditions (when ambient light forces reliance on rods).

Electrostatic lenses serve what purpose in the image intensifier?

Focusing and accelerating the electron beam from the photocathode to the output phosphor.

What is the primary factor limiting image detail in fluoroscopy?

Quantum mottle (noise arising from too few x-ray photons).

To minimize quantum mottle, what setting should the ABC preferentially increase?

mA (tube current).

The ratio of light output per unit of x-ray input is a measure of the image intensifier's...

Conversion factor.

What is the typical diameter of an image intensifier Output Phosphor?

1 inch (approximately 2.5 cm).

The acceleration of electrons across the image intensifier tube is powered by...

A high potential difference (often 25 kV or more).

Magnification mode on an image intensifier changes what?

Changes the focal point, using a smaller diameter portion of the input phosphor.

How does using magnification mode affect patient dose?

It increases patient dose (requires higher input exposure to maintain brightness).

How does magnification mode affect spatial resolution?

It increases spatial resolution (ability to see finer detail).

What is the component that reduces scatter radiation to the operator during fluoroscopy?

Bucky slot cover

Where is the x-ray tube typically situated for dose reduction?

Under the patient couch (underside operation).

What must be maintained for maximum image detail?

High brightness.

The measurement of brightness of an image display

Candela per square meter (cd/m^2).

What is vignetting in image intensification?

A reduction in brightness at the periphery of the image due to geometric distortion.

The ability of the eye to discriminate objects having small differences in brightness

Contrast perception.

What is Modulation in the context of image monitoring?

The signal processing applied to the video signal to adjust brightness and contrast.

Typical kVp levels for common fluoroscopic examinations often fall within what range?

70 kVp to 110 kVp (depending on the anatomical structure and contrast agent).

The purpose of using contrast media in fluoroscopy

To enhance the visibility of anatomical structures or fluid pathways.

What structure of the eye is responsible for color blindness?

Cones

The image monitoring system used for display in modern image-intensified fluoroscopy

Television monitor or flat panel monitor.

The term for dynamic studies of motion

Kinematography

Fluoroscopy requires specialized equipment to prevent eye strain because the visual system shifts between which two vision types?

Scotopic and Photopic.

Minimum separation required between the patient's skin and the input phosphor (Source-to-Skin Distance)

Limited by FDA Regulations (typically no less than 15 inches for fixed units).

The maximum table top entrance exposure rate permitted during standard fluoroscopy (according to FDA regulations)

10 R/min (100 mGy$_{a}$/min).

The ratio of the square of the input phosphor diameter to the square of the output phosphor diameter is called...

Minification gain.

The process where electrons are accelerated across the II tube to increase kinetic energy.

Acceleration potential.

The television camera system creates a visual image by scanning in what direction?

Linear pattern (rasters).

What is the typical vertical scanning frequency (field rate) for fluoroscopic television systems in the US?

60 fields per second.

The number of lines typically used to create a television frame in standard fluoroscopy.

525 lines.

A full television frame requires how many scan fields?

Two fields (interlaced scanning).

What is the critical component used in digital fluoroscopy (DF) that replaces the Vidicon camera?

A Charged-Coupled Device (CCD).

Advantage of using a CCD over a Vidicon camera

Higher spatial resolution, better signal-to-noise ratio, and greater sensitivity to light.

The image-intensifier input screen diameter (e.g., 9 inches) relates directly to what characteristic?

Field of View (FOV).

Where is the weakest point of light emission in the image intensifier system prior to the monitor?

Input phosphor.

What is the primary material used in the photocathode?

Antimony and alkali halides.

The term describing the degradation of image quality due to motion blur during lengthy procedures.

Lag or image blur.

How does increasing kVp generally affect patient contrast in fluoroscopy?

Decreases contrast.

The component of the image intensifier located immediately behind the photocathode that focuses the electron stream.

Electrostatic focusing lenses.

The ability to resolve small structures, usually measured in line pairs per millimeter (lp/mm).

Spatial Resolution.

What type of vision (rod or cone) provides the highest visual acuity?

Cone (Photopic vision).

The output of the image intensifier tube is coupled to the television camera using what method?

Fiber optics or lens coupling system.

The term used when the image intensifier is not perfectly centered, causing distortion.

Pincushion distortion.

What is the approximate size of a spot-film camera image capture size?

Varied (e.g., 105 mm or 70 mm).

In digital fluoroscopy (DF), images are often acquired and stored as...

Digital numbers (pixels) in a matrix.

The mechanism that prevents scatter radiation from exiting the Bucky slot opening.

Bucky slot cover.

Typical range of brightness gain in modern image intensifiers

Ranges from 5,000 to 30,000.

What happens to the mA when the ABC senses a brighter image?

It decreases the mA or kVp.

What happens to the mA when the ABC senses a darker image?

It increases the mA or kVp.

The conversion factor of an II tube is typically expressed in units of...

cd/m^2 per mR/s.

A type of distortion caused when too much input phosphor is used in magnification mode.

S distortion or Barrel distortion.

The primary role of Quality Control procedures in fluoroscopy.

To ensure consistent image quality while minimizing patient dose (ESD).

How is the brightness of the light image from the input phosphor controlled?

By the x-ray exposure (kVp and mA) used.

The maximum input dose rate for high-level control (HLC) fluoroscopy procedures (if equipped)

20 R/min (200 mGy$_{a}$/min).

If the Minification Gain is 81 and the Flux Gain is 40, what is the Brightness Gain?

3240 (81 x 40)

What is the primary disadvantage of using film recording (spot films) instead of digital recording during fluoroscopy?

Requires interruption of the procedure.

The term describing the random fluctuation in image density caused by insufficient photon flux.

Quantum mottle.

The device used in digital fluoroscopy to convert analog electric signals to digital values.

Analog-to-Digital Converter (ADC).

What is the function of the lead housing surrounding the image intensifier?

To protect the vacuum and provide shielding against leakage radiation.

The physical process where a single x-ray photon interaction results in multiple light photons at the input phosphor.

Scintillation.

The conversion of visible light to an electronic image at the photocathode is an example of what effect?

Photovoltaic effect (or Photoemission).

Viewing internal moving structures is part of which type of study?

Dynamic studies.

The range of light detection for the human eye, which is adapted for fluoroscopy.

Visual spectrum.

The part of the eye that contains the rods and cones.

Retina.

What technology is primarily used for fluoroscopic image display today?

Flat panel displays (LCD/OLED) or older CRT monitors.

A key advantage of digital fluoroscopy over image-intensified fluoroscopy.

Post-processing capabilities and reduction of image distortion.

What is the relationship between FOV and resolution in fluoroscopy?

Decreasing FOV (magnification) increases spatial resolution.

The movement of the electron beam during scanning across the target plate of a Vidicon tube.

Raster pattern.

If the input screen is 9 inches and the output screen is 1 inch, what is the Minification Gain?

81 ((9/1)^2)

The term for when the fluoroscopic image appears grainy.

Quantum mottle.