unit 5 review Flashcards
degree of geometric sharpness or accuracy of the structural lines of the image
recorded detail
what is the resolution of an image dependent on
pixel size(pitch), matrix size, & bit depth
how does phosphor layer thickness effect resolution
the thinner the phosphor layer the higher (better) the resolution
do you want a system with high or low spatial resolution?
high spatial resolution
what is the measurement of lines that can be seen on an image
spatial frequency
how is the trueness of an image determined
modulation transfer function (MTF) - measures the spread of light
anything that interferes with the formation of an image
noise
why would an image have a mottled appearance
lack of incoming photons to expose the IR , not enough mAs (increase/repeat)
the mathematical measurement of noise
noise power spectrum
do you want a high or low SNR , why?
high SNR , decreases noise
the processing function that averages the incoming analog data between the image detector elements (samples / scans pixels twice)
nyquist theory
what controls the sharpness of detail post processing
spatial frequency resolution
what are they types of motion
voluntary, involuntary, & equipment motion (moving grids)
how to control involuntary motion
decrease exposure time
how to control voluntary motion
communication
how to control equipment motion
lock equipment
how do distances effect detail
increase distance, increase detail
when you increase OID , detail
decreases
misinterpretation of size or shape of the structure being x rayed
distortion
types of distortion
size & shape (elongation & foreshortening)
factors affecting distortion
distances (SID), (OID), direction of angle, angle of part, CR, & IR
how is distortion & magnification calculated
M = SID over SOD
how to calculate actual size
object size = image size over mag factor
to avoid distortion - tube alignment
the part and IR must always be parallel & CR perpendicular
one of 2 geometric properties of the image (other is distortion)
recorded detail
other names for recorded detail
definition, sharpness, spatial resolution, detail
ability to record 2 adjacent structures as separate structures
definition
determined by matrix size, pixel size, and grayscale bit depth
recorded detail in digital imaging
the best spatial resolution has what kind of contrast
high contrast for small structures
what matrix size improves spatial resolution
larger matrix size
as resolution increases
recorded detail increases
the number of lines per millimeter that can be seen
special frequency
higher special frequency has
higher spatial resolution
expresses the boundaries of an image by testing the sharpness of lines
point spread function
fidelity or trueness of an image
modulation transfer function (MTF)
a system with an MTF of 1 would be
100% accurate
as background noise increases
image noise increases
SNR
signal to noise ratio
the measurement of contrast change present in an image
contrast to noise
to have a high CNR you must have
a high SNR
provides increased resolution when motion is present , the relationship between the duration of data acquisition and motion of the structures being studied
temporal resolution (TR)
shorter acquisition time will demonstrate
better TR (temporal resolution) - minimal motion
digital imaging should at least sample the pixels
twice, in order to form image
increases contrast & edge enhancement
high pass filtering
removes high frequency noise, reduces contrast
smoothing - low pass filtering
factors affecting recorded detail
geometry of the beam
focal spot
distance (SID) (OID)
motion
the distinctly sharp of a shadow or region of complete shadow
umbra
area of unsharp shadow around umbra
penumbra
as focal spot decreases, what happens to penumbra
decrease, increasing resolution
what does image processing do?
sets limits on detail
as motion increases
detail decreases
best control for involuntary motion
decrease exposure time
the only possible size distortion in radiography
magnification
is minification possible in radiography
minification is impossible because of divergence of the beam
misrepresentation by unequal magnification of the actual shape of the structure
shape distortion
shape distortion results from
how structures normally lie in the body
divergence of the x ray beam
tube, part, & IR alignment
object appears longer (tube or IR are improperly aligned)
elongation
object appears shorter (part is improperly aligned)
foreshortening
the tube angle will never cause
foreshortening
how to avoid alignment distortion
part & IR must always be parallel & CR perpendicular
when the nyquist theory isn’t met, the special frequency is greater than the inquest frequency
aliasing
equation to find which image will have better spatial resolution
pixel = FOV / matrix size
in image processing , what sets limits on detail
filtering, technical factors (LUT), histogram
