Image Acquisition Ch. 9

what are the sharpness factors

brightness and contrast

brightness (computer monitor) refers to…

window level

contrast refers to…

window width (grayscale)

contrast resolution deals with

bit depth

what is contrast-to-noise ratio

measure of contrast between tissue of interest and background (blackness)

what is high subject contrast

large difference between tissues

what is low subject contrast

small difference between tissues

what is spatial resolution (sharpness)

used to evaluate the accuracy of the anatomic structural lines

what is the formula for pixel size

FOV/matrix

higher the lp/mm, the higher the spatial frequency which =

smaller objects visualized

what is spatial resolution measured in

spatial frequency: line pairs/mm

what is modulation transfer function

measure of systems ability to see small objects

the higher the MTF, the…

higher the spatial frequency

what does pixel density/pixel pitch effect

the IRs ability to see small objects

what is pixel density/pixel pitch related to

the IR

what is dynamic range

ability to capture various energy levels of xray beam

what is exposure latitude related to

dynamic range

what is exposure indicator

numeric value tied to the amount of radiation striking the IR

radiation outside the exposure latitude of equipment is called…

saturation or quantum noise/mottle

what is saturation

more photons

what is quantum noise/mottle

too few photons

what is accurate measurement of exposure

detective quantum efficiency

what is detective quantum efficiency

ability of equipment to capture and record incoming photons

what is distortion

inaccurate recording of size or shape of anatomy

size distortion=

magnification

shape distortion=

elongation/foreshortening

what are artifacts

unwanted brightness on an image

magnification is increased by

increasing OID

what is DQE a measure of

dose efficiency

100% DQE=

no information loss

higher the DQE=

less radiation needed

what is subject contrast

differences in differential absorption of various tissues

decreasing kVp=

increases differential absorption and subject contrast

increasing atomic number=

increase subject contrast

increasing part thickness=

increase subject contrast

increasing scatter does what to the EI number

increases it

the AEC adjusts ___ to determine number of photons needed for image receptor exposure

time

as pixel size increases, spatial resolution…

decreases

pixels create the…

matrix

the higher the MTF, the ____ the visualized object can be

smaller

relating to MTF, 0 = 

no difference in brightness levels

relating to MTF, 1 =

maximum difference in brightness

what is signal-to-noise ratio

strength of radiation exposure compared to the amount of noise on an image

which of the following can also be referred to as size distortion

magnification

what is the relationship between the SID and size distortion

size distortion decreases with a longer SID

which of the following statements is true concerning OID and magnification

magnification increases with a longer OID

the distance between the anatomy being imaged and the focal spot within the x-ray tube is called

source to object distance

the highest quality radiograph would be produced by which of the following situations

longer SID and shorter OID

which reduces image contrast

noise

which is a measure of spatial resolution

MTF

which results in the highest subject contrast

50 kVp

which of the following affects subject contrast

differential absorption

which option will reduce patient dose while maintaining the EI

increasing kVp, decreasing mAs

patient radiation dose should be lower when digital imaging is used than when screen-film imaging is used, principally because of

DQE

if the dynamic range of an MRI system is 12 bits, how many shades of gray are present (2^n)

4096

the sensitivity that an imaging system has to record photons striking the IR is the

dynamic range

as the NUMBER of pixels increase, spatial resolution….

increases

as the pixel pitch increases, spatial resolution….

decreases

what is pixel pitch

distance between pixels

if there is a limited FOV, then the pixel size must become ____ to accommodate

smaller

with a limited matrix, the pixel size must ___ to accommodate

increase

large objects have ___ spatial frequency

low

small objects have ___ spatial frequency

high

what is the difference between spatial frequency and spatial resolution

spatial frequency is the amount of fine detail and spatial resolution is the systems ability to capture it

a quality radiograph must include

accuracy of structural lines displayed, minimal sharpness, and visibility of anatomical structures

unwanted scatter exposure to the IR will likely increase

fog

during digital image display, the contrast can be lowered by increasing _____

window width

double exposing an IR will likely result in

image artifact

kVp control

subject contrast

a change in body habitus changes the

subject contrast

ability of imaging system to distinguish between small objects that attenuate differently

contrast resolution

window width:

image contrast

the addition of contrast media

subject contrast

differential absorption:

subject contrast

a prosthetic hip alters the:

subject contrast

window level:

brightness

bit depth controls:

contrast resolution