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image capture problems "5"
systems setup and calibration
dynamic range
exp. field alignment
post read erasure
automatic rescaling

Image Capture Problems "9"
system setup and calibration
dynamic range
exp. field alignment
post read erasure
automatic rescaling
low intensity
scatter control

When discussing system setup and calibration, accuracy of exposure index determination and image appearance depends on
reader calibration
(derived exposure indices are worthless)
with system setup and calibration, processing codes identical on all readers unless ____
special codes required

(this avoids having to post process some images to optimize image appearance for radiologists preferences)

range of exposure(signal width) over which a detector can acquire image data
dynamic range
Digital Image acquisition systems are capable of capturing image data over a much larger ranges of exposures than ____. The increased dynamic range allow _____ to be captureed
screen film; anatomical info
with initial processing, eliminates signals outside collimation margins
automated exposure field recognition
uses shape of image signal distribution to determine
relevant info and exposure index
histogram analysis
mapping grayscale "values of intrest" to achieve specific display levels
automatic rescaling
provides images that have uniform display brightness over wide exposure range
automatic rescaling
automatic rescaling is based on ____
detector exposure
overexposed-rescales ____
bad things of automatic rescaling when it produces images that have uniform density brightness over wide exposure ranges "4"
false impress of large latitude

under some conditions rescaling fails

images will not display right contrast

dark light contrast

while the rescaled images have similar brightness(density levels) other ___
are not similar
underexposed---2 mas

noisy image-____

quantum mottle
overexposed--32 mas

contrast loss- edge loss
due to extra scatter
what is more critical with CR?
alignment of Structure/beam
Inappropriate beam configurations are from what?
histogram analysis errors (data in histogram that should not be there)
what field is the best when discussing alignment?
single field (centered to plate)
What field is ideal when discussing alignment?
four margins
which field is ok if part of field covers cassette midline
two margins
what alignments are unacceptable
not centered to plate

no marging between edge of plae and exposure field

3 margins

margin between edge of plate and exposure field

only ____contribute to image
exposed pixels
one exposure = ____
one detector readout
_______should be centered
tightly collimated images
image is read when?
immediately followin exposure
exposure field recognition errors (2)
histogram analysis errors

exposure index determination errors

Histogram analysis errors involve (2)
rescaling errors

dark, light low contrast images

exposure index determination errors indicate (3)

gross over exposure

gross under exposure

without evidence of mottle

with CR, expose ____ plate
use the small cassette to what?
reduce chance of histogram error
exposure field recognition error: (2)
field too small
rescaling error
what is a common practice with F/S
multiple fields
____is impossible with DR
multiple fields
multiple fields are allowed with ___
what would a vendor recommend?
sinle images and no collimation
why would a vendor choose a single image and no collimation?
reduces risk of histogram error

higher resolution on smaller pixel plate

once the data is extracte d from the plate, what happens
plate is erased
proper ____ensures data collected is relevant
proper _____removes irrelevant data from the image
digital detectors have a very _____
wide dynamic range
Digital Detectors are _____ than S/F systems
more sensitive
cassestte based PSP is a _____
storage phosphor
cassette based PSP is a storage stores what? and has what?
stores background exposure

grid not built in to cassette

grids generally indicated for any exam where remnant beam scatter is _______
50% of total beam
with a grid, chest ____
26 cm
other structures with a grid
grids carries risk of (3)
grid cutoff

degrades image contrast

moire effect

short dimension grid problems
moire artifact more likely
more likely with a stationary grid

laser scan parallel to grid lines
how to avoid moire
avoid grid frequency near nyquist

change sampling frequency

changing sampling frequency does what three things?
avoids moire

improves resolution

larger files

sampling frequency
the frequency in which data sample is acquired from the exposed detector
as receptor size decreases, sampling frequency _____ therefore spatial resolution ____
increases; increases
a measure of the ability of the imaging system to preserve signal contrast as a function of spatial resoltuion
every image can be described in terms of the amount of energy for each of its _____
spatial frequency
_____describes the fraction of each component that will be preserved in the captured image; often regarded as the ideal expression of hte image quality provided by the detector
spatial resolution
equal to one half the number of pixels/mm. ; dependent upon the the sampling frequency for PSP systems and the detector element size for flat panel systems
grid of cells in rows and columns
grid matrix
with an image matrix, each cell corresponds to what?
a specific location in the image
in the image matrix, the number in the cell represents what?
brightness or intensity at the location
the matrix size is determined by what?
the imaging equipment and computer capacity
Spatial Frequency refers to
line pair
he unit of spatial frequency is
line pairs per distance
If field of view remains the same, spaitial resolution ____as matrix size increase
Digital matrix size vary from
64X64 to 4096X4096
minimum matrix size is
at low spatial frequencies, MTF for radiography is ____ because of the two screen
contrast resolution is described as
grayscale or dynamic range
the ability to distinguish shades of gray from black to white
contrast resolution
100% contrast is _____
black and white
___is the controlling factor in CR and DR systems
dynamic range
the range of values over which a system can respond
dynamic range
the human eye has a dynamic range of app. ____
32 shades of gray
the exit beam can have a dynamic range of app. ___
1024 shades of gray
digital systems are characterized by their ____
dynamic range
8 bit means dynamic range of -___
2^8 or 256 shades of gray
the greater the dynamic range the better the ____
contrast resolution
MRI and CT require ____
12 bit dynamic range
with ______, the contrast in the region of interest can be enhanced
post processing
a bit dynamic range has ____shades of gray
_____allows for visualization of a portion of the dynamic range
____determines where to set the value for black
window level
_____determince how many shades of gray
window width
the electric response to the exit beam that represents anatomy
electric response to anything other than the subject
___limits contrast resolution
In general, as mAs increases SNR ____
MTF limited is maximized ___
MTF is controlled by ____
spatial resolution
contrast resolution is controlled by ____
with proper use of digital systems, dose can be reduced ___
Dose Creep
instead of 1 @ 50, you do 2 @ 50 and steadily go up
technique creep
1 @ 50, 1@52 it is good and what we should do
the _____ curve shows that contrast doesnt change with dose
linear dose response
with discussing receptor response, preferred method is to use lower mas and higher kvp, but at lower techniques
SNR issues become maximized
probability of xray interaction
detective quantum efficiency
DQE is highest in ____,

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