Radiographic Density Flashcards
Define Radiographic Density
Visibility of detail factor that describes the amount of blackness seen on an image (background blackness brightness indication)
What radiographic density is directly related to?
To quantity (amount) of radiation reaching IR
When sufficient radiographic density is achieved
When the bony and soft tissue structures of interest are visualized
What mAs is controlling factor of?
quantity or amount of radiation
What an increase and decrease in mAs will do to Radiographic Density (with adequate penetration)
increase= increase in Radiographic density decrease= decrease in radiographic density
What excessive mAs demonstrates on image
Density that is so dark that some or all of bony and soft tissue structures of interest are not well visualized it will be too dark
How to determine between if too much mAs or kVp was used on a dark image
evaluating the image contrast
What an overexposed image using too much mAs demonstrates
acceptable contrast as long as kVp used is optimal
How an overexposed image using too much mAs will appear
overall dark, the cortical outlines of the bone should remain high in contrast
What an underexposed image using insufficient mAs demonstrates
Density that is so light that some or all of the anatomic structures cannot be seen or evaluated
How an underpenetrated (kVp) image will appear
image will not demonstrate the cortical outlines that were not penetrated
Controlling factor of image density
mAs
what 30% change in mAs will demonstrate?
adjusts the image density just enough for the eues to be able to visualize that a change was made
When is it ideal to use the 30% rule
when an image demonstrates acceptable but not optimal density and needs to be repeated because of a factor other than density (artifact, motion)
what will a change in mAs be on an image that is borderline too light
100% increase in mAs
what will a change in mAs be on an image that is borderline too dark
50% decrease in mAs
what will a change in mAs be on an image so light or dark it will have to be repeated
3-4 times the increase or decrease in mAs
How kVp affects radiographic density
is affected by a change in kVp because it alters the quality of photons
How mAs compensates for insufficient kVp if possible
NO AMOUNT
Define optimum kVp
kVp that will provide adequate part penetration and sufficient gray scale
How image that has been adequately penetrated will appear
demonstrates the cortical outlines of the thinnest and thickest bony structures of interest
what factor is automatically set with AEC
mAs
what factor technologist must set with AEC
optimum kVp level
Define minimum response time
the time it takes for the circuit to detect and react to radiation received
with reference to AEC what results in underexposed images
failure to properly activate correct ionization chambers and to not center the anatomic structure over them
when using the AEC why its important to use tight collimation
to reduce scatter radiation that may cause the AEC to shut off prematurely
what situations or conditions will prohibit you from using AEC
when any type of radiopaque hardware or prosthetic device will be positioned over activated chamber
What changes the 1 button and 2 button imply when using them for density control
1- 25% density change
2- 50% density change
What increasing SID does to radiographic density
decreases
what decreasing the SID does to radiographic density
increases
what is the % of change in SID for a visible density change
20%
how increasing OID affects density
could result in a noticeable density loss
what must be done to mAs when changing to a higher grid ratio and how this will affect density
increase mAs, or insufficient density
what must be done to mAs when changing to a lower grid ratio and how it affects mAs
decrease in mAs
How to distinguish grid cut off from other density problems
appearance of grid lines on the image
what the amount of density change depends on
field size and the amount of scatter that would typically reach IR
why compensating filter is used
to offset the thickness difference and obtain optimum density throughout entire images
how you should set your technique when using a compensating filter
set a technique that will adequately penetrate the thickest portion of the anatomic structure of interest
when you should use Anode Heel Effect
when positioning long bones and the vertebral column when a long 17” field length is used
which end produces more photons
cathode
when using anode heel effect what part of structure will be placed under anode end of the tube and cathode end of the tube
anode-thinner side of structure
cathode-thicker side of the structure
what part of tube represents + or - symbols
\+= anode - = cathode
how mAs should be set with anode heel effect
to adequately demonstrate the midpoint of structure (where CR will enter)
what using anode heel effect demonstrates on the finished image
a more uniform density across the part
