Part 2: Equipment Flashcards
What make fluoroscopy images brighter?
Image intensifiers
X-ray tubes in fluoroscopy usually operate at ___ to ___mA
3 to 5
Cathode filament and anode in X-ray tube are both made of what?
Tungsten
What makes tungsten a better producer of X-rays?
High melting point
High atomic number
Purpose of image intensifier
Electronically amplify brightness of the image
Purpose of each part of image intensifier:
- Vacuum bottle/glass envelope
- Input layer
- Electronic lens
- Output phosphor
- Keep air out
- Convert X-rays to electrons
- Focus the electrons
- Convert energy of electrons into visible light
Brightness gain is the ability of the ___ to increase the illumination level of the image
Image intensifier
Brightness gain is the product of what 2 things?
Minification gain
Flux gain
Minification gain is simply ___, NOT ___.
Increase in brightness or intensity
NOT improvement in quality
Does a smaller or larger image intensifier produce a better image?
Smaller
When is a 9” vs 6” mode used for image intensifiers?
9”: large anatomic areas
6”: better image quality but size is unimportant
What affects image intensifier image quality? (4)
- Quantum mottle
- Contrast
- Resolution
- Distortion
Mottle is more visible in a (high/low) resolution, (high/low) contrast system
High, high
Mottle can be adjusted by changing what two exposure factors?
kVp and mA
The ratio of brightness between two adjacent areas of a fluoroscopy image is called what?
Intensifier contrast
Is contrast better with cesium iodide or zinc cadmium sulfide tubes?
Cesium iodide
Contrast ratios for modern image intensifiers exceed ___
15:1
What happenes to an image intensifier if the input phosphor does not absorb all the photons in the X-ray beam?
Contrast is diminished
What happens to an image intensifier if there is retrograde light flow from the output phosphor?
Diminishes contrast
What portion of the image intensifier has the greatest resolution?
The central portion
Bigger intensifier = (more/less) distortion
Why?
More
Because the further an electron is from the center, the more difficult it is to focus
What kind of distortion is the consequence of projecting the image on a curved input phosphor to a flat output phosphor?
Pincushion distortion
When is pincushion distortion reduced?
When magnification modes are used
With pincushion distortion, the image is magnified to a greater extent towards the (center/periphery), resulting in ___.
Periphery
Vignetting
What part of the fluoroscopy unit keeps the light output of the image intensifier constant over variations of pt thickness and density (attenuation)?
Automatic brightness control (ABC)
The ABC interfaces with the ___ to adjust kVp and mA in a quick feedback loop
X-ray generator
Operating fluoroscopy at higher kVp values results in what happening with the beam?
Increased transmission of the beam through the pt = less radiation required
If kVp was increased by 15%, how much change in brightness would occur? How much would the ABC adjust the mAs?
15% increased in kVp = double brightness = mAs reduced by 50%
What happens to image contrast as kVp is increased?
It degrades
When should lower vs higher kVp be used?
Lower: low contrast objects/iodine based contrast (angio, chole, etc.)
Higher: high contrast/barium (GI, etc.)
4 types of ABC circuits
- Variable mA, preset kVp
- Variable mA with kVp following
- Variable kVp with selected mA
- Variable kVp, variable mA
What does being a closed circuit video system mean?
The video signals are transmitted via cables rather than air
What does the vidicon tube of the vidicon camera contain?
The vidicon target
the electron gun
How does the vidicon tube produce a television picture?
The electron gun produces the electron beam that is focused onto the vidicon target which produces the picture
What is the downside to vidicon tubes?
Image lag
What is interlaced scanning in a closed circuit monitor system?
The odd lines of the produced image are scanned first then the even lines are rescanned with the same image
A vidicon camera (enhances/reduces) contrast by a factor of 0.8 and the monitor (enhances/reduces) contrast by a factor of 2.
This results in a net (improvement/deterioration) of the image contrast.
reduces
enhances
improvement
Traditionally, how many scan lines per picture are produces with a fluoroscopy television system?
525
What factors affect television image quality in the normal closed-circuit fluoro system? (5)
Horizontal resolution
Vertical resolution
Contrast
Brightness
Lag
Horizontal resolution is the sum of what three things?
scan lines + frame rate + frequency rate
Vertical resolution (lp/mm) = ?
horizontal lines across the image
_______________________________
2 x diameter of object in mm
Formula for the Kell factor
vertical resolution
___________________
# scan lines
What is the Kell factor for a 525 scan line system?
0.7
What is lag?
When the television image is blurred when the fluoroscopic tower is moved rapidly
Is lag caused by the image intensifier?
No
Which type of camera is used for CV procedures due to better contrast and less motion blurring?
Plumbicon camera
What are some advantages of the charge-coupled device (CCD) cameras?
Smaller unit
Lower power consumption
Lower price
Longer life
Less lag
What are the two typical ways of recording dynamic (motion) images with analog devices?
Video tape recording
Cinefluorography
There is an up to 95% patient dose reduction when utilizing ___ during fluoroscopy
video disc recording.
____ photograph the image on the output phosphor of the image intensifier
Photospot film cameras
Which has higher radiation dose rate per frame: fluoroscopy or spot film cameras?
Why?
Spot film cameras dose 20-50x higher per frame rate
Used much higher mA
A 70mm roll film in a spot film camera can acquire up to ___ frames/sec.
12
With an individual spot film camera, what happens to pt dose and image quality as film size increased?
Both increased
Which has lower pt radiation exposure: an individual 105mm spot film or a cassette-loaded spot film?
Always the individual spot film
Where is the spot film positioned?
Between the pt and the image intensifier
Spot-filming mA with conventional cassette
100+
Analog-to-digital converter
Digital-to-analog converter
ADC: converts the original data to store an image in digital processor memory
DAC: converts the stored digital image back into analog so it can be viewed
3 basic types of studies performed with digital fluoro.
Which is most used?
- Mask mode fluoro (most used)
- K-edge fluoro
- Time interval difference imaging
What type of imaging:
Pros: instant playback, possible subsequent image enlargement
Con: resolution is less than that of film
Digital photospot imaging
Regulations limit the maximum tabletop dose rate of ____ when acquiring images without a recording device such as video tape.
20 rad/min
High level fluoroscopy is generally used for what procedures?
Interventional/cardio/angio
Rate the image intensification viewing systems from highest to lowest resolution:
optical mirror
videotape
video (real-time)
16mm cine film
35mm cine film
spot cassette
spot 105mm
spot 70mm
digital
highest: optical mirror
cassette spot
105mm spot
70mm spot
35mm cine
16mm cine
digital
video real-time
lowest: videotape
High or low pt radiation dose?
spot film
photospot/digital
cine
videotape/disc
spot: high
photospot/digital: low
cine: high
videotape/disc: low
Framing frequency for each:
spot film
photospot/digital
cine
videotape/disc
spot: 1/sec
photospot/digital: 12/sec
cine: 60/sec
videotape/disc: 60 rpm
