Plus minus chart Flashcards
What is the degree of blackening?
Density
What is the number of different shades of gray?
contrast resolution
What is the misrepresentation of size or shape of an object?
Distortion
What is the sharpness of structural lines?
recorded detail
What is the ability to image small parts?
spatial resolution
Distortion is controlled by what?
distance (SID)/angle of tube
Recorded detail is affected by?
SID, OID, Patient thickness
Distortion and recorded detail are related how?
inversely- when one increases/decreases opposite happens to the other
What is mAs?
the number of xrays
If mAs increases what happens to density?
increases (it is proportional)
If mAs increases what happens to patient dose?
patient dose increases because the amount of xrays going to the patient is higher
If mAs increases what happens to contrast?
no effect
If mAs increases what happens to distortion?
no effect because there is no change in distance or angle on tube
If mAs increases what happens to recorded detail/spatial res?
no effect (ex: sign on road at night its still there just gets darker)
If time (exposure time) increases what happens to density?
increases because image gets darker as exposure increases
If time (exposure time) increases what happens to contrast?
no effect
If time (exposure time) increases what happens to distortion?
no effect
If time (exposure time) increases what happens to recorded detail/spatial res?
decreases, expose longer= more time for patient to move= image gets blurry
If time (exposure time) increases what happens to patient dose?
increases
If kVp increases what happens to density?
increases, if kvp increases mas is halved if kvp decreases mas is doubled (15% rule)
If kVp increases what happens to contrast?
Decreases
If kVp increases what happens to patient dose?
decreases, if kvp increases there is more penetrability = less patient dose, if kvp decreases there is less penetrability= more patient dose
If kVp increases what happens to distortion?
no effect
If kVp increases what happens to recorded detail/spatial res?
no effect (image is still recorded doesn’t matter if we see it because its still there)
What controlls kVp?
contrast/scatter/penetrability
High kvp=_____ scale
short
Low kvp=____ scale
long
If SID increases what happens to density?
decreases (less beam at the IR)
If SID increases what happens to contrast?
no effect
If SID increases what happens to patient dose?
decreases (the greater the SID the less dose)
If SID increases what happens to distortion?
decreases (greater SID= decreases magnification)
If SID increases what happens to recorded detail/spatial res?
Increases (inversely related to distortion)
If OID increases what happens to density?
no effect
If OID increases what happens to contrast?
increases (if air gap) no effect if regular
If OID increases what happens to patient dose?
no effect
If OID increases what happens to distortion?
increases
If OID increases what happens to recorded detail/spatial res?
decreases (inversely related to distortion)
Higher OID= _____ contrast
shorter
Roles of OID?
Air gap technique, acts as a grid
If Patient thickness increases what happens to density?
decreases
If Patient thickness increases what happens to contrast?
decreases (more scatter=decrease contrast)
If Patient thickness increases what happens to patient dose?
increases
If Patient thickness increases what happens to distortion?
increases (more OID)
If Patient thickness increases what happens to recorded detail/spatial res?
decreases (inversely related to distortion)
For a thicker patient you would use ____ kvp which equals ____ scatter?
more, more
OID _____ if patient thickness increases?
increases
If field size (collimation) increases what happens to density?
increases (open film is blacker)
If field size (collimation) increases what happens to contrast?
decreases (expose more tissue= more scatter)
If field size (collimation) increases what happens to patient dose?
increases
If field size (collimation) increases what happens to distortion?
no effect
If field size (collimation) increases what happens to recorded detail/spatial res?
no effect (effects visibility but the image is still there)
If voltage waveform increases happens to density?
increase (more xrays in beam= more penetrability)
If voltage waveform increases happens to contrast?
decrease
If voltage waveform increases happens to patient dose?
decrease
If voltage waveform increases happens to distortion?
no effect
If voltage waveform increases happens to recorded detail/spatial res?
no effect (image is still recorded doesn’t matter if we can see it)
Ripple half wave is?
100%
full wave?
100%
3 phase 6 pulse?
14%
3 phase 12 pulse?
4%
high frequency?
1%
If less ripple=____ technique needed?
lower
If filtration increases what happens to density?
decreases (less photons hitting the IR)
If filtration increases what happens to contrast?
decreases ( higher energy beam hits IR= high scale contrast=less gray)
If filtration increases what happens to patient dose?
decreases
If filtration increases what happens to distortion?
no effect
If filtration increases what happens to recorded detail/spatial res?
no effect (image is still recorded)
High scale contrast=_____ gray
less
If grid ratio increases what happens to density?
decreases (less photons hitting the IR)
If grid ratio increases what happens to contrast?
increase (reducing scatter allows higher energy photons to hit the IR)
If grid ratio increases what happens to patient dose?
increases
If grid ratio increases what happens to distortion?
no effect
If grid ratio increases what happens to recorded detail/spatial res?
no effect
The job of the grid ratio is to?
increase contrast
If focal spot size increases what happens to density?
no effect
If focal spot size increases what happens to contrast?
no effect
If focal spot size increases what happens to patient dose?
no effect
If focal spot size increases what happens to distortion?
no effect (no angle or change in distance)
If focal spot size increases what happens to recorded detail/spatial res?
decrease (smaller focal spot= more recorded detail, bigger focal spot=worse detail)
Focal spot size is a determining factor that effects?
spatial resolution
Where is the effective focal spot located?
@ tube window
Where is the actual focal spot located?
anode
If contrast media increases what happens to density?
decreases (less density if more contrast)
If contrast media increases what happens to contrast?
increases
If contrast media increases what happens to patient dose?
no effect
If contrast media increases what happens to distortion?
no effect
If contrast media increases what happens to recorded detail/spatial res?
no effect ( adding contrast doesn’t change recorded detail it makes it easier to see detail)
If film speed increases what happens to density?
increases (doubles density)
If film speed increases what happens to contrast?
no effect (darks and lights decreases but the space between stays the same)
If film speed increases what happens to patient dose?
decreases
If film speed increases what happens to distortion?
no effect
If film speed increases what happens to recorded detail/spatial res?
decreases (reduces detail)
If film speed increases use ____ xrays?
fewer
Increase film speed= ____ sensitive
more
Film speed controls the?
number of xrays (ma/time/mAs)
If screen speed increases what happens to density?
increases
If screen speed increases what happens to contrast?
no effect
If screen speed increases what happens to patient dose?
decreases
If screen speed increases what happens to distortion?
no effect
If screen speed increases what happens to recorded detail/spatial res?
decreases
Soft tissue and extremity use what technique?
low kVp high mAs