Ch. 30 - Digital Image Preprocessing and Processing (Rescaling)
As part of gradation processing, once a volume of interest (VOI) aka Region of Interest (ROI) is chosen (correcting the correct part/exam done) only this range of pixels will be sent/compared to the ...
Look Up Table (LUT).
Would the barium and light shield be factored into rescaling reconstruction?
No
Can PPR be used with a FPD (flat panel detector)?
No, only with CR
_______________ is an attempt to make the image more like a conventional radiograph by simple alignments to image brightness prior to any post-processing
Normalization
Preprocessing image analysis can include __________ which identifies (prior to EI) areas of noise and associated densities outside of the collimated field.
Segmentation
In addition to exposure field recognition, CR units must also employ ____________or __________ ________ _________ software that can count and separate multiple views taken on a single PSP plate
Segmentation, Partitioned Pattern Recognition
In DR, individual dexels or detector elements can drop completely out of the image due to ... and what is this commonly called?
TFT failure (thin-film transistor) or switching transistor malfunction, "dead pixels"
Which type would have a raw radiation spike on the right side whose data from this area is not sent to Look Up Table (LUT)?
TYPE 1
Which type has no spike or tail?
TYPE 2
Which type of histogram analysis is designed for a study with positive contrast like barium or the presence of a lead apron and has a tail on the left side?
TYPE 3
Explain interpolation in your own words.
When you have a dead pixel you can use interpolation to figure out how bright that pixel was supposed to have been. Look at the surrounding 8 pixels, a kernel, which would be 9 because it includes the middle one which is dead. You average the brightness level of 8 pixels which is known data to figure out the unknown brightness of the dead pixel in the middle and then turn it on.
Provide two reasons why an Smin and Smax must be established if there are excessively light values.
barium and/or lead shield
The proper type of histogram analysis must be matched with the acquired histogram for images that contain a background _______, radiopaque __________ or large bolus of ______.
density, prostheses, barium.
Flat Field uniformity is designed to even out the brightness across an imaging field that could be caused by?
dropped or dead pixels
Q values are stored in the ?
permanant LUT
Explain a histogram in your own words.
A histogram is a graphical representation of all the pixels in a given image and the particular brightness buckets that they fall into or how many pixels fall into each brightness level.
X-axis on a histogram is related to
amount of exposure or pixel value (density)
What does Exposure Field Recognition (EFR) assist with in both computed radiography (CR) and digital radiography (DR)?
analyzing background densities outside of the anatomy
The EI is coming from the ________ of the Smin and the Smax
average
Digital systems may correct for dead pixels through a process of _________ where an average of the ___ pixels surrounding the dead pixel are utilized to fill it in with a more appropriate grey scale.
interpolation, 8 surrounding pixels
Software can be configured to fill in pixel values for dead hardware pixels, and to adjust for flat-field non-uniformity, by __________.
interpolation.
Most rescaling (normalization) methods use software that algebraically re-labels input pixel values such that the _______ values are always the same. To accomplish this, the range of _______ acquired must match the range of _______ in a permanent output look-up table (LUT).
output, S-values, Q-values
Exposure field recognition (EFR) prevents black densities _______the anatomy from being included in histogram analysis.
outside
Image analysis includes p_________ p_______ r__________ or s__________, e________ f_____ r_________, construction of the initial histogram, and histogram a________. Each of these steps must be correctly executed for the following procedures to result in a proper image.
partitioned pattern recognition or segmentation, exposure field recognition, construction of the initial histogram, and histogram analysis.
A histogram is a graphic representation appears as a series of _____ and _______ and has a pattern that varies for each body part
peaks and valleys
Post processing is redoing ___________
preprocessing
Processing errors can occur if the histogram chosen at processing which is a ____________ __________ does not match the actual histogram acquired on the image (mismatch).
procedural algorithm
Contrast changes for example can be altered however these functions are exactly the _____ that are done during initial processing and if the default processing is successful there would in reality be no need for post-processing.
same
The type of histogram analysis used must match the ______ of the actual histogram obtained.
shape
To avoid processing errors, we must be able to anticipate the general ______ of the acquired histogram to be expected for different types of anatomy
shape
Rescaling is accomplished via a __________ approach.
software
On the displayed histogram for an image, a ________ gray scale curve indicates higher contrast in the image.
steeper
Field ___________ corrections include adjustments for flaws in digital acquisition hardware and del drop-out effects.
uniformity
In rescaling, all data from the Smin to Smax are relabeled algebraically and then compared to a ____ with pre-determined ___ values based on the __________ _____ of the software (ie. zero - 4095)
All data from the Smin to Smax are relabeled algebraically and then compared to a LUT with pre-determined Q values based on the dynamic range of the software (ie. zero - 4095)
How are dead pixels typically addressed in digital systems?
By interpolating neighboring pixel values
Which imaging modality is affected by Partitioned Pattern Recognition (PPR) inaccuracies, potentially leading to a rescaling error and a change in brightness?
CR only
Of the variables listed which affect flat field uniformity, which are the only two that apply to direct-capture DR?
Electronic Response and Gain Off-sets
If there was a raw radiation spike, what would help remove it?
Exposure Field Recognition (EFR)
The area between the Smin and Smax is the Savg and is utilized when creating the ...
Exposure indicator (EI) number.
What is the term for correcting an imaging field that could be caused by dead pixels by evening out the brightness?
Flat field uniformity
Because the slope of curve A is shallower than curve B, what does that indicate about contrast and the speed of change in brightness?
If it's more shallow that means that it'll travel slower through gray scales so there will be more grays and lower contrast
What method is commonly used to fill in dead pixels with gray scale?
Interpolation
What compares brightness level and contrast to manufacturer's histogram?
LUT or look-up table
__________ changes ie bone vs soft tissue and metal is accounted for in the histogram.
Landmark
Which software is used exclusively with CR and can separate fields of collimation?
Partitioned Pattern Recognition (PPR)
The grayscale curve gradation gradient has the log relative exposure on which axis? and the brightness of the pixels on which axis?
Pixel exposure on the X-axis and brightness on the Y-axis
_____________ can be seen as manipulation of the image after corrections have already been made for data acquisition carried out to refine and subject to _______ ____________
Post processing, personal preference.
_____________ is your choice to redo preprocessing like windowing for contrast and leveling for brightness.
Post processing, you didn't like what the algorithm gave you to begin with
Which process refines the image based on personal preference after initial corrections to the raw image data?
Postprocessing
___________ can be considered correction to the raw image data due to physical flaws in image acquisition inherent to the elements and circuitry of the image receptor
Preprocessing
refer to the specific output values assigned to each input pixel value with a dynamic range.
Q-values
__________ is designed to give you an image that most people would find acceptable, the computer is trying to produce contrast and brightness of what historically has been considered a diagnostic image
Rescaling
The term ___ values to refer to incoming data that has not yet been rescaled, and ___ values for rescaled (processed) data.
S values to refer to incoming data that has not yet been rescaled, and Q values for rescaled (processed) data.
Which shape does the curve on a typical histogram exhibit, indicating the contrast of the displayed image?
S- shape
For histogram analysis, the desired portion of the main lobe to be used, between points SMIN and SMAX, is referred to as the
S-avg or average pixel value
What does the transition from left to right on a histogram indicate regarding the anatomy?
The anatomy exhibits darker densities
Why does DR require more preprocessing than CR?
The dexels, within DR (direct capture) suffer from various electronic faults not found in CR
True or false: Processing errors occur during the mathematical processing and happen regardless of proper exposure technique.
True
EFR is utilized by looking at anatomical landmarks also known as ...
VOI- volumes of interest
Once a __________________ is chosen (correcting the correct part/exam done) only this range of pixels will be sent/compared to the Look Up Table (LUT)
Volume/region of interest
Preprocessing consists of corrections for flaws in the __________ of the original image, image analysis and ___________.
acquisition, normalization.
What does the huge spike at the far right of a histogram indicate in a small chest that does not cover the entire image receptor?
background radiation (raw radiation)
Histogram "A" is chosen to accentuate _____ anatomy aligning the VOI to the left at the expense of the soft tissues to the right.
bony
The histogram can be viewed as a curve with bright areas on the ____ (bone, contrast, metal) and darker areas on the _____ (air/gas).
bright areas on the left (bone, contrast, metal) and darker areas on the right (air/gas).
Histogram is designed so that ________ levels are more towards the left, ______ levels towards the right
brighter - left darker - right
The rescaling process is able to correct the __________ level of almost any input image (provided that there has been sufficient exposure to produce full original information).
brightness
On a typical histogram, as we move from left to right the ________ of the pixels is changing from _______ to ______.
brightness (density), lighter to darker
PPR can work incorrectly when borders of _________ are not accurately recognized causing a rescaling error and a change in brightness.
collimation
The computer can adjust the levels and ranges of pixel values, but cannot change the pixel ______ for any particular value
count
For example, ____ related to pixels can suffer from electronic faults (more in DR than CR) that would create noise and requires more pre-display processes.
dels
The histogram identifies all _______ on the imaging plate in the form of a graph.
densities (brightness levels)
In a flat-field uniformity test, how many areas of the field are sampled and compared for consistency?
five areas of the field, the center and four corners
What is designed to even out the brightness across an imaging field that could be caused by dropped/dead pixels?
flat field uniformity test
A steeper gray scale curve superimposed over the histogram indicates ________ image contrast.
higher
The steeper the curve on a grayscale curve the _______ the contrast
higher
Taking known data that is correct and applying it to something unknown or that you want to solve can be termed as
interpolation
What is the mathematical process called by which a kernel averages surrounding pixel values in order to fill a dead pixel from a faulty dexel?
interpolation
The overlay of a separate matrix is known as a ______ and can consist of how many pixels?
kernel, 9
Applying threshold algorithms to each side of the histogram with values being stored only when a certain number of pixels are reached is used to
landmark identification on histogram
For an acquired histogram with a bizarre shape, failure to properly locate the expected ___________ is a common cause of digital processing errors.
landmarks
To analyze a histogram, the computer scans in from each end of the data set, searching for identifiable _________ created by changes or trends in the pixel counts in each "bin" or file.
landmarks
Histogram analysis requires the sorting of image data based on pixel values alone, regardless of the location of these values within the original matrix. To "know" where modified values must be inserted within the spatial matrix to reconstruct the final image, the computer ...
logs and stores the location of each pixel value by its matrix designation before histogram analysis begins.
In normalization, what is the purpose of the rescaling?
makes simple alignments to the brightness and contrast to give the user a "normal" view of the radiograph.
Why was PPR useful for CR specifically?
multiple views on one cassette in CR image plate
If the full IR is used, there should be no ... that would normally be removed by Exposure Field Recognition.
no background/raw radiation
Raw data used to form the histogram of a body part is compared with a "_______" histogram of the same body part by the computer.
normal
Y-axis displays on the histogram the ...
number of pixels for each exposure (pixel count)
EFR utilized in CR & DR helps in histogram analysis by analyzing background densities outside the anatomy like ____ __________ by looking at anatomical landmarks also known as ____
raw radiation, volumes of interest (VOI).
After initial histogram analysis, a ____ image is created. If this were displayed however, without rescaling, it would look ...
raw, washed out and/or without contrast.
The __________ step results in the final displayed image that makes simple alignments to the brightness and contrast to give the user a "normal" view of the radiograph.
rescaling
The _____ spike is because of using less than the full IR
right
A common histogram will have no spike on the right side because ...
the body part took up the entire image receptor
Which side of a histogram has more attenuation?
the left side which is brighter
A common method is to apply __________ algorithms to each side of the histogram with values being stored only when a certain number of pixels are reached.
threshold
The ____ is a range within the histogram that can be relocated to accentuate different tissue types in the image.
volume or values of interest (VOI)
Flat field uniformity can be tested for by examining the pixels across an exposed field without a ______/_______ and at a ____ exposure (4 corners and center)
without a phantom/object, low exposure
