Part 1: Factors impacting pt dose Flashcards
To reduce pt exposure, you want to use ___ kVp and ___ mA
HIGH kVp
LOW mA
To reduce pt exposure you want to use ____ image intensifier mode with strict ____
Largest
Collocation
To reduce exposure you want to keep the patient to detector distance or patient to image intensifier distance as (long/short) as possible
Short
In fluoroscopy, the x ray output/pt radiation dose is (directly/indirectly) proportional to the mA used
Directly
X-ray tube voltage is what unit?
kVp
What is kVp used to determine?
The maximum photon energy in keV of the X-ray beam produced
Most important step to take to avoid unnecessary pt radiation exposure
Collimation!
Good collomation means the X-ray beam is (increased/reduced)
Reduced
More colliamtion = lower size of X-ray beam = ?image quality?
Improved
Because X-ray tubes in fluoroscopy operate at 125-150 kVp, filtration must be at least how much?
3mm aluminum equivalent
___ inch target to panel distance is optimal for fluoroscopy.
___ inch is the minimum
18” (fixed unit, ideal amount)
12” minimum (mobile unit)
On fluoroscopy system equipped with ABC where X-ray tube is fixed to table below, moving the image intensifier AWAY from the pt (increases/lowers) pt radiation dose
Increases
The image intensifier serves as primary protective barrier and must be at least ___ of lead equivalent for equipment operating about 125 kVp
2mm
Bucky slot cover
Caused when Bucky tray is moved to the end of the table and leaves a 2” wide opening at operator’s gonad level
Bucky slot cover must be at least ___ lead equivalent
0.25mm
Protective curtain drapes of at least ___ lead equivalent must be positioned between fluoroscopist and patient
0.25mm
Doubling the exposure time does what to pt radiation dose?
Doubles it
The input phosphor absorbs ___ and converts their energy into ___
X-rays -> light photons
In an image intensifier, after X-rays are converted to light photons, the light photons are immediately absorbed by the ___ which causes ___ to be given off in direct proportion to the intensity of the fluorescent light.
Photocathode
Electrons
In an image intensifier, after the electrons are given off, they are sped up by the ___ and focused with little distortion by ___ onto the ___.
Accelerating anode
Electrostatic lenses
Output phosphor
In an image intensifier, the output phosphor (screen) absorbs electrons and emits ___ which are then available for processing by the video system.
Light photons
How is brightness gain in the image intensifier achieved?
By acceleration of the electrons and minification of the output image
Aka electronic gain and minification gain
What is quantum mottle?
A grainy or blotchy appearance to the image which is due to a low number of absorbed photons
The mottle level can be adjusted by changing what?
Exposure factors (kVp and mA)
How do you increase the number of available X-ray photons?
Increase exposure
Most fluoroscopists use ___mA in manual mode for adult fluoroscopy to marinating adequate X-ray photon stability?
2 to 5
How is subject contrast reduced in general?
With high kVp
Subject contrast is chiefly determined by what?
The kVp
Detector contrast is determined by what?
Image intensifier
Type of tv camera target
Amplitude of brightness/signal
Brightness/contrast settings on monitor
What units are used to measure resolution?
Line pairs per millimeter (lp/mm)
Overall resolution of an image is expressed in what terms?
Modulation transfer function (MTF)
Size distortion is caused by what?
Shape distorts caused by what?
Size: object to image distance
Shape: geometric problems in shape of intensification tube
What is the cause of vignetting?
The peripheral image is displayed over a larger area of the output screen causing brightness loss at the periphery
What part of the image intensifier changes the field of view from standard to magnification mode?
Electrostatic lens
Fluoroscopy TV systems are ___ systems
Closed circuit
___ is the operation of camera shutters at the same frequency as X-ray pulses.
Synchronization
Framing frequency in cinefluorography is usually a division of ___
60
(E.g. 7.5, 15, 30, 60, 90, 120)
A higher lens f-number means what?
Less light is available to form the image on the cine film
There is an up to 95% dose reduction when utilizing ___ during fluoroscopy.
Video disk recording
What two advantages to video tape recording have over cinefluorography?
- Instant replay of the image
- Pt radiation exposure is not increased
Does video tape or cinefluorography have a fixed frame rate of about 30/sec?
Video tape
When spot filing, you place the cassette between ___ and ___.
The patient
The image intensifier
What makes spot film cassettes have the best resolution?
They’re made using higher mA (100+) with short exposure time (less motion)
They’re acquired with very high resolution cassette detectors
Contrast media is chosen based on what two qualities?
Low toxicity
High atomic number
What is the function of a radiographic grid?
To reduce scatter radiation produced in the pt before it reaches the image intensifier or X-ray film
What is a cassette front made out of?
Low atomic number material (carbon fiber, aluminum, cardboard)
Pro and con of 35mm cine film vs. 16 mm
35mm: more pt exposure, higher image quality
Cinefluorography is almost entirely utilized on which organ?
Heart
Cinefluorography delivers about how much more radiation dose than fluoroscopy for the same kVp?
10 times
What are the most important factors in attenuation and absorption?
Tissue density
Elemental composition
What is remnant radiation?
The primary radiation that exits the human body
Minimum source to skin distance for mobile fluoroscopy units.
Minimum source to skin distance for stationary fluoroscopy units.
With some circumstances, absolute minimum?
Mobile: 30 cm or 12”
Fixed: 38 cm or 15”
Absolute: 10 cm or 8”
Scatter radiation is mainly produced by ___
Compton interactions
What 3 factors affect an increase in scattered radiation?
- High kVp
- Large field exposed (area exposed)
- Thick body part (volume exposed)
Minimum source-to-tabletop distance?
Should be <38 cm or 15”
Absolutely not <30 cm or 12”
