Ch. 26 Density / IR Exposure Flashcards
- Identify image receptor (IR) exposure as a prime component of the photographic
component of the properties controlling visibility of detail of radiographic image
quality.
- Identify image receptor (IR) exposure as a prime component of the photographic
-Visibility of detail refers to the fact that the image is visible to the human eye only b/c sufficient IR exposure/ density (and contrast) exist to permit the structural details to be perceived.
- Differentiate between density and IR exposure.
-Traditional term “density” no longer applicable in digital world
Replaced with image receptor (I R) exposure. density is the overall
blackening of the film.
- Describe the effects of IR exposure changes on the image appearance.
Increase density/ IR exposure = darker image
Decrease density/ IR exposure = lighter image
- What are the 3 different noise types?
-Quantum noise (quantum mottle)
-System noise
-Ambient noise
-Best method of assuring that both EI and noise values are appropriate is to use automatic exposure controls (AECs) and anatomical programming
4.1 what is Quantum noise (quantum mottle) ?
-Refers to a lack of sufficient incoming data for processing
Results in blotchy or mottled image
Solution is increase the number (or quanta) of incoming signals
by increasing the mAs of an x-ray beam
4.2 what is System noise?
-This is caused by electronic components w/i the digital image receptor
4.3 what is Ambient noise?
Caused by background radiation
- what is the process of evaluating IR exposure?
-the major consideration in assessing ir exposure on film is verification that proper
densities are visible throughout the anatomical area of interest on the image
- the ability to assess ir exp is a result of continued conscientious eval of images
during clinical expr.
-assesment of ir exposure on a digital image can not be based on visual cues due to
digital system’s post-processing capabilities
-ir exposure must be evaluated using target exposure index value (EI1)
- What are the 10 influencing factor affects IR exposure? (mAs)
- mAs (primary)
-(25-30% change of mAs for visible density change)
- What are the 10 influencing factor affects IR exposure? (kVp)
-affects scatter
-can affect shape of histogram
-15% rule: 15% change in kvp causes doubling or halving of exposure image
receptor
-kkvp change not recommended to control image noise
- What are the 10 influencing factor affects IR exposure? focal spot size
- not affect density/IR exp.
-blooming results from high mA selection
- What are the 10 influencing factor affects IR exposure? anode heel effect
-The anode heel effect refers to the variation in radiation intensity and
subsequent Image Receptor (IR) exposure between the anode and cathode ends of the x-ray tube.
Depending on the angle of the anode, this effect can lead to an IR exposure difference of up to 45
percent between the two ends of the image, with exposure being greater at the cathode end. This
effect is more pronounced when the collimator is wide open
- What are the 10 influencing factor affects IR exposure? Distance: SID
- (Source to Image Distance) impacts x-ray exposure
by the inverse square law
(I1/I2) = (d2^2/d1^2)
-Exposure maintenance – maintain exposure if distance is altered:
(mAs1/mAs2) = (D1/D2)^ 2
- What are the 10 influencing factor affects IR exposure? Distance: OID
-OID: when distance is increased between object and IR will decreas exp;
reduces scaatter
- What are the 10 influencing factor affects IR exposure? filtration
-increased filtration will decrease IR exposure
beam restriction
-Reduces total amount of remnant radiation striking IR (reduces scatter
and secondary)
