chapter 10 xray physics Flashcards
Image quality defined as?
is the fidelity of anatomical structures by the image
the most important factors affecting quality of the image?
resolution
noise and artifacts
what are the 2 different forms of resolution
spatial and contrast
noise is defined as in an image?
random variation in optic denstiy of image
what is optic density?
how much light can be transmitted through
which of the 5 basic interaction of matter are considered important when it comes to noise?
compton because it deals with scatter e-
what is film grain and how does it contribute the image?
it is finite small silver crystals that make up the image itself
how does film grain affect the noise?
larger the film grain the more noise there is
what are structure mottles?
they are large phosphor crystals of the intensifying screen
how does structure mottles contribute the noise?
the larger the mottle structre the more noise there is
how does speed affect the noise and resolution?
as speed increases the higher the noise is and the lower the resolution is
how does higher speed affect the pt. dose and heat production?
as the speed increases the pt. dose decreases and the heat damage to the anode decreases
slower speed has what affect on the image?
the resolution will increase but the pt. dose will increase and the heat damage to the anode
the characteristic curve is used for _____ systems?
analog
characteristic curve is for analog systems and it shows a response curve for xray films that demonstrated what characteristics?
density, contrast, speed, latitude
When a xray machine uses film what characteristics of processing must you take into consideration?
time and temperature
characteristic curve shows a relationship between what?
optical density and the radiation exposure.
how would optical desntiy appear on the film?
as different shade of grey
what happens to the optical density as the radiation exposure increases?
it becomes more black so it will increase
what is another name for the characteristic curve?
hurter and driffield or H & D curve
contrast of the radiographic image refers to the?
difference between the gray shades that comprise the image?
the straighter the line is of the H & D curve shows what?
represents that any change in the exposure will make a greater change in film
the straighter the line represent the film has what?
greater contrast OR Less contrast?
greater contrast in response to the exposure
when looking at a characteristic curve you can notice which one is faster by noticing what about the exposure?
how much radiation exposure it takes
the human eye can perceive optical densities in between what range?
0.25 (clear) and 2.5 (black)
the xray film base is of what material?
polyester
what is the OD of the xray film base?
0.1
what is added to the xray film base to reduce glare in the view box?
blue dye
how would you describe fog when it comes too OD?
any additional OD to the on a processed xray film that does not have a purpose will result in fog
why is base and fog measured?
for quality control
what is a desnitometer?
measure the OD of materials such as the film
Base + fog should not exceed?
and should not be lower than?
- 3
0. 25
the latitude of the H & D curve demonstrates what?
the amount of exposure
what does the magnification factor show a relationship between?
image size and object size
focal film distance is also known as?
source image distance
SOD is known as
source object distance
OID is known as
object image distance
what do measure by dividing SID by SOD
the magnification
how does a smaller object distance affect the shadow?
it will get smaller
is you increase the OID what happens to the magnification?
it gets bigger
if you decrease the SOD or the OID what happens to the shadow?
it will get bigger
how would a longer SOD affect the magnification?
reduces magnification
distortion is defined as?
uneven magnification
what may contribute to distortion
size
shape
position/orientation
how does the shape of the object affect the shadow?
directly
how does the shape of an object affect the grey shade?
does not change
when considering object position what is important?
object symmetry with the image source
as the object thickness what happens to the edge sharpness?
there will be 1/2 shadow area
why is an objects orientation in space important?
a distorted image that apears foreshortened will be produced the more lateral to the central axis it lies
due to distortion in the apparent length due to the orientation of space is the apparent length a good indicator to actual size?
no
how does kVp effect the contrast changes?
higher kVp produces lower contrast with longer scale of grey shades and lower kVp produces higher contrast image with shorter scale pf grey shades
kVP is the controlling factor of what?
contrast
the mAs is the primary controlling factor of what?
film exposure
why does short exposure times yield better image quality?
reduced pt. motion,
