chapter 6: image characteristics and shadowing casting

what are factors that affect image characteristics?

1. beam characteristics

2. receptor features

3. operator technique

4. object radiodensity

what is radiodensity?

the ability of x-radiation to pass through particular materials

what is radiolucency?

dark areas of a radiograph

are radiolucent areas more or less dense?

less dense

what does radiopaque mean?

opaque to radiation

what does opaque mean?

not see through

what happens in radiopaque material?

x-rays are absorbed/resisted

what do radiopaque objects appear as?

white

what is density?

the overall darkness/blackness of a radiograph

what factors affect density?

1. kilovoltage

2. milliamperage

3. exposure time

4. subject thickness

what is contrast?

the difference in blackness 

what does high contrast consist of?

stark blacks and whites 

what does low contrast consist of?

many shades of gray

what factors affect contrast?

kVp, NOT mA

what does increasing kVp do to contrast?

decreases contrast

what does decreasing kVp do to contrast?

increases contrast

what are the 2 scales of contrast?

short scale and long scale contrast 

what is short scale contrast?

high contrast (black and whites, little grays)

what is long scale contrast?

low contrast (lots of shades of gray)

what does an increase in mA do to density?

increases density

what does a decrease in mA do to density?

decreases density 

what does an increase in kVp do to density?

increases density 

what does a decrease in kVp do to density?

decreases density

what does an increase in exposure time do to density?

increases density

what does a decrease in exposure time do to density?

decreases density

what does an increase in subject thickness do to density?

decreases density 

what does a decrease in subject thickness do to density?

increases density

what does an increase in kVp do to contrast?

decreases contrast

what does a decrease in kVp do to contrast?

increases contrast

what are examples of geometric characteristics?

sharpness, magnification, and distortion 

what is sharpness?

the capability of the receptor to produce distinct outlines of an object

what is penumbra?

lack of sharpness

what factors affect sharpness?

1. focal size

2. film composition

3. movement

how does focal spot size affect sharpness?

the smaller the focal spot, the sharper the image

what does a smaller focal spot mean for sharpness of image?

smaller focal spot = sharper image 

what does a bigger focal spot mean for sharpness of image?

larger focal spot = less sharp image

how does film composition affect sharpness?

emulsion of faster film has larger crystals, causing less sharpness

how does movement affect sharpness?

more movement = less sharpness

what is umbra?

complete shadow 

what is penumbra?

the shaded region of shadow cast by an opaque object

what factors affect magnification?

target/receptor distance and object/receptor distance

what does a longer PID and target/receptor distance do to magnification?

lesser magnification

what does a shorter PID and target/receptor distance do to magnification?

larger magnification 

how does an increase in object/receptor distance affect magnification?

increases magnification 

how does a decrease in object/receptor distance affect magnification?

decreases magnification

what is the paralleling technique?

long PID = less divergence = less magnification

what factors affect distortion?

object film alignment and x-ray beam alignment to object and receptor

what does the object-receptor alignment being parallel do to distortion?

decrease in distortion 

what does the object-receptor alignment not being parallel do to distortion?

increase in distortion

what does the x-ray beam alignment to object and receptor being perpendicular do to distortion?

decreases distortion

what does the x-ray beam alignment to object and receptor not being perpendicular do to distortion?

increases distortion