w13 exposure and IQ

when we have good brightness on an image, what can we say about the beam? explain

there was good attenuation; some xrays penetrated while some were absorbed

T or F: brightness can be digitally adjusted by our software systems + brightness settings of our display monitors

true

define contrast

the difference between the brightness of two adjacent structures

what thing can negatively impact our contrast

scatter reaching the IR

define greyscale

the range of different brightness levels (or shades of grey) within an image

what is a long grey scale

many different shades of grey

what is a short grey scale

only a few shades of grey

does low contrast have a long or short grey scale

long

to improve contrast resolution, what do we manipulate

mAs

define spatial resolution

the smallest object that can be detected in a digital image

what is spatial resolution determined by in DR systems

detector element size

describe detector element arrangement in DR systems

matrix; arranged in rows and columns

in CR imaging, what is spatial resolution determined by

the frequency of sampling of each area of the plate being laser stimulated

which has better spatial resolution: DR or film systems

film systems

which is better for pt dose: DR or film systems

DR

what test do we use to test a system’s spatial frequency

line pair test tool

describe the line pair test

contains pairs of thin dense wire with increasing narrow spaces between the line

what unit is used for the line pair test

line pairs per mm

for the line pair test, what counts as “one line pair”

the solid line and the adjacent space beside it

for DR systems, what spatial resolution do they have (using the line pair test)

7lp/mm

what does MTF stand for

modulation transfer function

what is modulation transfer function (MTF)

expresses the ability of a system to accurately demonstrate small objects

what is the range of MTF

0-1

what is the ideal MTF value

1

when would we have an MTF of 1

when the image appears exactly as the object

what happens to MTF as an image becomes blurrier

lowers

T or F: for DR, you cannot image an object smaller than the pixel size

true

from high to low frequency, what happens to the MTF curve

decreases

define dynamic range

the detector’s ability to accurately capture the range of photon intensities that exit the pt

do digital image receptors have a wide or narrow dynamic range

wide

what do we see on the image at the low end of the dynamic range

mottle

what do we see on the image at the high end of the dynamic range

burnout

T or F: inherent image noise exists in all digital imaging systems due to electronic components

true

T or F: manufacturers manage electronic noise using fiber optics and direct transmission methods

true

what is quantum mottle

when too few photons reach the plate

what causes quantum mottle (3)

low mAs, low kVp, dense structures

what does it mean when there is a high signal to noise ratio

high signal = lots of data for our system to create the image with, low noise

which is better: high or low SNR

high

what is dose creep

when we keep increasing the dose but a lower dose still would’ve given us the same IQ

how to prevent dose creep (2)

look at EI values, pay attention

define exposure latitude

the range of acceptable exposure values that we can use while still producing a usable image

what is window width

the number of grey shades represented

what is window level

the range of grey shades on the scale represented

do dense structures appear light or dark

light

wider window width = more or less shades of grey?

more

wider window width = higher or lower contrast?

lower

narrow window width = more or less shades of grey?

less

narrow window width = higher or lower contrast?

higher

T or F: we can adjust WW and WL

true