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Glossary of Bennett Test 3-7,8,11,12,28

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Accuracy of exposure index determination and image appearance depends on...
reader calibration
Vendor must use ___________ to calibrate reader to target exposure index, otherwise image will be too dark or light
dosimeter
range of exposures (signal width) over which a detector can acquire image data
dynamic range
the range of values over which a system can respond (contrast resolution)
dynamic range
What has a larger dynamic range, F/S or CR/DR?
CR/DR
Digital detectors have a _____________ exposure response
linear
Typical digital systems respond to exposures as low as ____ and as high as ______
100 microRoentgens; 100 milliRoentgens
________ is about 2 days background exposure. Background exposure is about ________ each day
100 microRoentgens; 60-80 microRoentgens
Dynamic range _______ exposure latitude
IS NOT
Dynamic range of F/S is about __________
1000
The human eye has a dynamic range of __________
32 shades of gray (5-bit; 2^5)
The exit beam can have a dynamic range of _________ shades of gray
1024 (2^10; 10-bit)
Digital systems are characterized by their....
dynamic range
8-bit has a dynamic range of...and intensity level of...
2^8, or 256 shades of gray (intensity level of 0-255)
MRI and CT have a ____ dynamic range
12 bit
Digital radiography has a ____ dynamic range
14-bit
Mammo has a ____ dynamic range
16-bit
Histogram analysis uses shape of image signal distribution to determine:
-Relevant info in exposure field
-Exposure index
software function that maps the grayscale to the values of interest (VOI) in the histogram to achieve specific display levels
automatic rescaling
When does automatic rescaling occur?
When exposure is greater or less than the optimal amount to produce a diagnostic image
Automatic rescaling produces images with uniform ___________ over a ____________, regardless of ______________
brightness and contrast; wide exposure range; amount of exposure
Automatic rescaling uses ______________ to correct exposure errors
histogram shape recognition
Problems occur with automatic rescaling when too little exposure is used (leads to....) and when too much exposure is used (leads to....)
noisy image (quantum mottle); loss of contrast and loss of distinct edges due to extra scatter
Alignment of structure/beam (exposure field) with IR is more critical in ___ than in ____
CR/DR; F/S
Inappropriate beam configuration can lead to...
histogram analysis errors
Small fields (less than ____ of plate) should be centered
1/3
Multiple fields are common with ___, allowed with ____ under certain rules, and not possible with ___
F/S; CR; DR
In CR, multiple images may be put on 1 plate as long as they are...
symmetric (same size; same relative area)
For CR, vendor probably recommends ___ image per plate and _____ collimation
1; no
Proper __________ ensures the data collected is relevant
centering
Proper ________ removes irrelevant data from the image
collimation
In what is scatter control more important, F/S or CR/DR?
CR/DR
Grids are generally indicated for any exam where remnant beam scatter is greater than ____ of total beam.
Chest > __ cm
Other structures > _____ cm

50%
26
10-12

Grid use carries risk of _______ and/or ________
grid cutoff; moire effect (aliasing artifact)
When does moire effect occur?
Because of grids or computer error.
Occurs when alignment of grid to laser scan direction is incorrect (laser parallel to grid lines) OR when spatial frequency is greater than Nyquist frequency and sampling occurs less than twice per cycle (when sampling frequency is close to grid frequency)
Moire with cassetteless flat panel detector occurs when exposure times are...
greater than 10 msec
To reduce risk of moire
avoid grid frequency near Nyquist
change sampling frequency
larger files



Preprocessing is controlled by...
software and technologist
In preprocessing, you select __________, __________, and _______
projection; orientation; speed class
graphical representation of intensities recorded on imaging plate
histogram
process of determining what values to include in the histogram
histogram analysis
Exposure data recognition (histogram analysis) processes only...
the optimal density exposure range
If system fails to find collimation edges, images may be...
too bright or too dark
when laser traverses plate and causes light emission
image sampling
investigating or evaluating a segment of the image
image sampling
Low energy (kVp) gives a _______ histogram; high energy (kVp) gives a _______ histogram
narrower; wider
Histograms are different for ________________ and remain fairly constant from patient to patient
specific anatomic regions
when sampling a signal, the sampling frequency must be greater than twice the bandwidth of the input signal so that the reconstruction of the original image will be nearly perfect
Nyquist theorem
the highest spatial frequency that can be recorded by a detector
Nyquist frequency
1/2 the number of pixels per mm
Nyquist frequency
Nyquist frequency is determined by...
pixel pitch
Nyquist is __________ by slow scan movement
reduced
Nyquist frequency predicts ___________ in CR
maximum spatial resolution
For example, if pixel density is 10 pixels/mm, max spatial resolution (Nyquist frequency) is 5 lp/mm
table of the luminance values derived during image acquisition
lookup table
image mapping function in which all pixels are changed to a new gray value
lookup table
_____ is used as a reference to evaluate the raw info and correct the luminance values
LUT
LUTs are only used in...
digital imaging
LUTs are assignments that are specific to each...
anatomic part
LUTs are used to assign ______________ to ___________
colors (gray values; brightness values); histogram values
LUT will have a more vertical slope for ________ window width, and more horizontal slope for ________ window width
narrow; wide
__________ can be increased or decreased by changing slope of LUT graph
Contrast
_________ can be increased or decreased by moving the line of the LUT slope up or down the y-axis
Brightness (density)
range of exposures that can be used and still result in the capture of a diagnostic quality image
exposure latitude
In CR, if exposure is more than ____ too low, mottle is seen.
In CR, if exposure is more than _____ too high, contrast loss is evident
50%; 200%
a measure of how well the image can accurately image an object
MTF
the ability of the system to accurately represent the imaged object
MTF
the ability of a system to record available spatial frequencies
MTF
a measure of the ability of the imaging system to preserve signal contrast as a function of spatial resolution
MTF
ratio of image to object as a function of spatial frequency
MTF
mathematical procedure for determining resolution
MTF
____ is a way to quantify the contribution of each system component to the efficiency of the entire system (to total resolution)
MTF
The closer the MTF is to ______, the better the resolution
1 (100%)
At low spatial frequencies, does mammography or radiography have a higher MTF?
Radiography, since radiography uses 2 screens
MTF is controlled by...
spatial resolution
High-contrast can image ____ objects, while low-contrast can image ______ objects
small; large
DR has higher MTF at _____ spatial frequencies due to...
lower; large dynamic range and higher DQE
The _____ the pixel, the smoother the image appearance
smaller
The ______ the area of pixel values averaged, the smoother the transition of brightness levels
larger
What is the result of smoothing (low-pass filtering)?
reduced noise and contrast
When is smoothing (low-pass filtering) useful?
For visualizing small structures such as fine bone tissues
The _______ the area of pixels averaged, the more the contrast and edges are enhanced
smaller
Edge enhancement occurs when ______ pixels in the neighborhood are included in the signal average
fewer
when some signal values are suppressed while others are strengthened (this enhances contrast and edge)
high-pass filtering
High-pass filtering can aid in visualizing....
large structures like organ edges, but it can be noisy
suppressing signal (suppressing frequencies of lesser importance)
masking
Masking can result in...
loss of small details
The most common image processing parameters are those for....
brightness (window) and contrast (level)
___________ allows us to visualize a portion of the dynamic range
windowing
What controls # of shades of gray to display?
window width
What determines the value that will be the darkest on the image (where to set value for black)?
window level
What removes excess light from image that would result in veil glare?
Shuttering/black border/background removal
____________ allows images to be sent to more than 1 computer or destination
manual send
function that allows retrieval of archived images from PACS
archive query
grid of cells in rows and columns
image matrix
the number in each cell in the image matrix represents the ___________ at that location
brightness (intensity)
What determines matrix size?
The smallest matrix size (ex. imaging equipment/IR, computer, and monitor)
the ability of an imaging system to resolve and render on the image a small high-contrast object
spatial resolution
What is human eye spatial resolution?
200 micrometers
Spatial frequency refers to the....
line pair
Low spatial frequency are _____ to image; high spatial frequency are ______ to image
easy; hard
High spatial frequency-->Spatial resolution is _______
better
What determines spatial resolution in CR?
sampling frequency
What determines spatial resolution in DR?
DEL spacing (pixel size)
What determines spatial resolution in F/S?
FS size
If field of view remains the same, spatial resolution increases as matrix size __________
increases
Minimum matrix size for radiography is...
2048x2048
(so cells of IR, computer, and monitor must each have a minimum of 2048x2048 cells)
the ability of the system to distinguish between many shades of gray from black to white
contrast resolution
contrast resolution is described as...
grayscale; dynamic range
If dynamic range is 2, the 2 shades of gray are...
black and white (100% contrast)
What controls contrast resolution in CR/DR systems?
Dynamic range and SNR
As dynamic range _______, contrast resolution gets better
increases
What has better contrast resolution, CR/DR or F/S?
CR/DR
electric response to exit beam that represents anatomy
signal
electric response to anything other than subject
noise
Is it possible to have a noise-free system?
No, all systems have some inherent noise
As mAs increases, SNR... and contrast resolution...
increases; increases
What determines image detail (spatial resolution)?
System MTF
What reduces contrast resolution?
Noise
plot of minimum visual size as a function of contrast
contrast-detail curve
Left side of contrast-detail curve is related to...and is limited by...
high-contrast objects; MTF of imaging system
Right side of contrast-detail curve is related to...and is limited by...
low-contrast objects; noise (SNR)
Lower curve in contrast-detail curve represents _______ contrast resolution
better (since tissue with lower subject contrast can be imaged)
With proper use of digital systems, patient dose can be reduced by...
20-50%
Why should patient dose be less with digital imaging than F/S imaging?
Because of higher DQE and linear IR response
Low mAs and high kVp is preferred, but at lower techniques noise ____ and SNR _____
inc; dec
indicates the potential "speed class" or dose level required to acquire an optimal image
DQE
a measure of the efficiency with which the SNR of the incident exposure is preserved in an image
DQE
____ is a measure of x-ray absorption efficiency
DQE
What has highest DQE? CR, DR, F/S
DR has highest, then CR, then F/S
PACS consists of...
image acquisition, display workstations, and archive servers
The software that makes PACS usable across many networks is...
DICOM
What allows images acquired in any modality to be viewed at any display?
DICOM
medical image on display monitor
softcopy
What is the most interactive component of a PACS system?
display workstation
What has replaced viewboxes?
display workstations
How many monitors are used for diagnostic workstations?
2 generally (to compare)
What is the most important piece of the workstation?
Monitor
What are the 2 ways a digital image is displayed?
As digital image composed of shades of gray, and as histogram
Cross-sectional imaging is read on __K monitor. CR and DR on __K monitor. Mammo on __K monitor
1; 2; 5
Physician review station is __K. Technologist QC station is __K
1; 1
how a process is done, step-by-step; throughput
workflow
computers that act as file room of PACS
archive servers
What are used as the central hub for images sent to PACS and images viewed by doctors?
archive servers
the hardware and software infrastructure of a computer system
system architecture
Common system architectures with PACS:
-Client/server-based
-Distributed (stand-alone)
-Web-based

In what PACS system architecture are images sent directly to the archive server after acquisition and are centrally located, but application software is locally loaded?
Client/server-based
What is client in client/server-based system, and what is server?
Display workstation. Archive server
What is PACS workflow where acquisition modalities send the images to a designated reading station and possibly review stations, so each workstation "archives" and PACS archives?
Distributed (stand-alone) systems
system architecture in which images AND application software for client display are held centrally
web-based system
how images will be displayed on a monitor
hanging protocols
What type of imaging uses cine function most often?
Cross-sectional imaging, such as CT or MRI, which has lots of images to scroll through in a stack
Radiation safety, PPE, linearity, reproducibility are part of __ activities
QC
Most QC activities are part of an overall...
QA program
3 major categories of QC test
-acceptance testing
-routine maintenance
-error maintenance

CQI focuses on...
the processes of QC/QA programs, not on individual performance
Quality is both _____________ -centered
people and product
a plan for systematic observation and assessment of the different aspects of a project, service, or facility to ensure that standards of quality are being met
quality assurance
a comprehensive set of activities designed to monitor and maintain systems that produce a product
quality control
Why are members more likely to participate in CQI?
Because it focuses on processes, not individual performance or mistakes
ACR recommends use of ____________ test pattern
society of motion pictures and television engineers (SMPTE)
AAPM recommends use of ________ test pattern
TG18 (comprehensive)
ACR recommends QC tests be performed _____, and AAPM has a _____ rigorous schedule
monthly; more
AAPM recommends that tests be done for acceptance ______ by a trained _______
annually; physicist
Routine QC tests are performed by...
trained technologists or physicists
What is the weakest link in the digital imaging chain?
Monitor
What do you use to measure luminance response?
TG18-LN test pattern and photometer
All readings on TG18-UN test pattern should be within __% of each other
30
What is tested using TG18-CT pattern?
angular response
Speed in QC refers to processing speed of _____ and ____________ rate
workstation; retrieval/transfer
What is used to reduce size of image files to increase speed of network transfer of images?
Compression
To test compression recall...
save several images of TG18-QC test pattern with different compression ratios (no compression, lossless compression-2:1 ratio, lossy compression-variable ratios)
Who primarily recognizes undiagnostic images?
Radiologist
Who does system training for PACS?
PACS administrator or superusers
QC standards for image acquisition, processing, and equipment maintenance contribute to...
TQM
QC standards are covered by...
ACR recommendations and AAPM report #3
Who is the first line in preventing, recognizing, and reporting QC issues?
Techs

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