Exam 1 Flashcards
ability to img small objects that have high subject contrast
spatial resolution
the random fluctuation in the OD of the img
noise
2 other terms for spatial resolution
detail, recorded detail
what factors affect the visibility of detail
img contrast and OD
what is quantum mottle? how does it appear on the img?
the random nature by which XRs interacts w/ IR. If produced w fewer XRs, quantum mottle increases; causes grainy appearance
how do you minimize quantum mottle?
high mAs, low kVp, slow IR
what’s contrast resolution?
ability to img 2 separate objects and visually distinguish btw the 2
how does speed affect detail?
fast IRs = high noise, low spatial/contrast resolution slow IRs = low noise, high spatial/contrast resolution
what is sensitometry?
study of relationship btw intensity of exposure and blackness (density) on img
what is on the x and y axis on a sensitometric curve?
X-axis: LRE, y-axis: OD
3 parts of a characteristic curve?
- toe, 2. straight-line portion, 3. shoulder
what part of characteristic curve represents optimum contrast?
straight-line portion
what part of characteristic curve represents over exposure?
shoulder
what part of characteristic curve represents under exposure
toe
density can be measured using a
densitometer
formula for calculating OD?
OD=log(Lo/Lt); Lo - original light, Lt - light transmitted
what is the diagnostically useful density range for an XR?
0.25 - 2.5
what is the range for base plus fog density?
approx 0.1 - 0.3
radiographic contrast is the product of ______ and ______
IR contrast & subject contrast
film contrast is related to the ______ of the _______ part of the characteristic curve
slope & straight-line
how do you calculate the slope of a characteristic curve
calculate the avg gradient
what is the formula for calculating avg gradient?
avg gradient = (OD2 - OD1)/(LRE2 - LRE1); OD2 - OD of 2.0 + base and fog densities (LRE2 assoc w OD2); OD1 - OD of 0.25 + base and fog densities (LRE1 assoc w OD1)
how do you ID the faster characteristic curve?
faster films located to the L of slower films (on x-axis) (curve closest to y-axis)
how do you ID the characteristic curve that has more contrast?
steeper slope –> higher contrast