Test 2 Flashcards
short scale/high contrast
very black and white 40kvp
long scale/low contrast
many shades of gray 110/120
magnification factor =
SID/SOD
direct square law formula
mas1/mas2=(d1)2/(d2)2
inverse square law formula
I1/I2=(d2)2/(d1)2
what are the factors affecting xray quantity?
- mAs
- kVp
- distance
- filtration
xray quantity
the number of xrays in the useful beam
mA=
quantity of xrays produced
more mA =
darker the image
the number of xrays produced is
directly proportional to the exposure time
longer exposure time =
darker image
shorter exposure time =
lighter image
xray quality
the penetrating power of the xray beam
xray quality =
kVp
as kV increases,
the speed of electrons traveling from cathode to anode increases
high kV =
more gray image and more penetrability
low kV=
too dark of an image
“soft” xrays don’t penetrate as well
reciprocity law
any combo of mAs and time will yield the exact amount of optical density
exposure = intensity * time
optical density
the degree of blackening on a radiograph
what determines you OD
mAs
what is the reciprocity law used for
- control motion
- change focal spot
- utilize breathing technique
noise
the grainy or uneven appearance of an image caused by an insufficient number of primary xrays
what is noise caused by?
- film graininess
- structure mottle
- quantum mottle
- scatter radiation
quantum mottle
the random nature in which xrays interact with the IR
a result of uneven intensity
quantum mottle decreases
recorded detail
slower film using more xrays =
good resolution
faster film using less xrays =
not as good resolution
latitude
the margin of error in technical factors
amount of leeway you have when taking an image
higher the kV the more latitude
what are the 3 geometric factors
- magnification
- distortion
- focal spot blur
magnification
increase in the object’s image size compared with its true or actual size
as OID increases
magnification increases
as OID decreases
magnification decreases
as SID increases
magnification decreases
as SID decreases
magnification increases
how to minimize magnification
use a large SID
use a small OID
object size =
image size/MF
MF = magnification factor
percent magnification
image size - object size divided by object size x 100
shape distortion
the unequal magnification of different portions of the same object
2 ways shape distortion appears
- elongation
2. foreshortening
elongation
image of an object appears longer than the actual object
what causes elongation?
the object is parallel and straight with the IR but the tube is angled or
the tube and part are straight, but the IR is angled
foreshortening
and image of an object that appears shorter than the object itself
what causes foreshortening?
when the object or anatomical part is angled
any structure that is not positioned at the CR will be
distorted because of the divergence of the beam
the farther from the CR,
the greater the distortion
spatial distortion
the misrepresentation in the image of the actual spatial relationships among objects
