physic chapters 20-22 Flashcards
what is a histogram
a graphic rep. of exposure received to the pixel elements and the likelihood of those exposures within the image inside the collimated area
what should be checked on the menu before exposing a patient
check for correct anatomic region
what is compared to the raw data histogram?
a normal histogram with the same anatomical part
values of interest (VOI)
the range of histogram data set that should be included in the displayed image. (contrast would be too low if all shades were left
the less the exposure to the receptor what is created on the histogram
light color
ex. the spin denser than the lung tissue so that is why the spin appears white and the lungs appear dark
what type of range does digital radiography allow
wide dynamic range
what is dynamic range?
it is a leaner relationship between exposure and the resulting pixel value
what are some problems with a wide dynamic range
too low of an exposure can result in noise
too high of an exposure leads to high patient exposure
how does a high S number correlate with exposure and how does low S number correlate with exposure and S number?
low exposure= high S#
high exposure= low S#
what causes blurring in a digital image
FSS, motion, receptor (light spread from the screen phosphors), and pixel size which is the ratio of the FOV (field of view) snd the matrix size
what are the Y and X axis of a histogram
Y axis= # of pixels and X= VOI (values of interest; pixel value
what is a histogram analysis error
in CR the entier imaging plate is scanned to extract the image from the PSP. (if at least three edges are not identified, a histogram error could occur
what is a look up table (LUT)
is a reference histogram which maps the grayscale values
how are LUT values graphed
original values on the X- axis and the new values on the y-axis
how can the LUT graph control contrast (what aspect of the graph)
contrast can be increased or decreased by changing the slope of its graph
how can LUT control density
brightness is controlled by increasing or decrease moving the line up or down the Y-axis.
how does the LUT image contrast transfer function work
basically the original image is altered which leads to diff. pixel values then the final image is processed, causing diff. contrast levels.
(this is the reason why we can have a wide dynamic range)
digital annotations
manual text and preset terms (EX. FLEXION AND EXTENSION, PORTABLE/UPRIGHT)
should you use digital annotations to identify patients Lt. or Rt. side?
no
in digital CR what happens during Quantization by the ADC
each pixel represents a gray shade that is given a number value that controls the shades of gray
what is pixel depth ?
determines brightness level available for image display
(fixed in the system by the ADC
what happens when you increase pixel depth in regards to contrast resolution
increased contrast resolution
what is image stitching?
is a computer process that allows images to be joined when the anatomy is too large for one exposure
what should be used during a scoliosis series?
image stitching
what is smoothing?
filters out high frequency noise
( does this when frequency in each pixel is averaged with surrounding pixel values)
reduction of noise and contrast
what is another name for smoothing
low-pass filtering
what is edge enhancement (cath)
average of signal to shorten processing time and storage
what is high-pass filtrations definition? (Cath)
averaging of the signal to shorten processing time and storage
what is another term for high-pass filtration? (Cath)
edge enhancement
what contrast does edge enhancement provide (Cath)
allows the visibility of high contrast structures
veil glare
unexposed borders around the collimation edges allow excess light to enter the eye
what chemical that is over-sensitized causes glare/white light blinding
rhodopsin
shuttering
blocking the light coming from the unexposed area (which is white and causes vail glare)
when does Automatic rescaling occur
this occurs to display the pixels for the area of interest (zooming).
resizing of the image matrix
when rescaling what are some problems that occur when we have an underexposed image
this results in quantum mottle
when rescaling what are some problems that occur when we have an overexposed image
loss of contrast and loss of distinct edges b/c of + scatter production
what kind of images are produced when automatic rescaling occurs
images with uniform density and contrast regardless of amount of exposure
what is QC
anything that deals with instrumental/ equipment
what are types of QC
tools used to measure EI, AEC calibration, image plate cleaning, Alignment and collimation test tool, focal spot size, kVp calibration, timer, linearity, reproducibility
QC in relation to Alignment and collimation test tool
indicators within 2% of SID and centering within 1% of SID
QC in relation to Focal spot size (diff. tests)
Pinhole camera; star pattern and slit camera
QC kVp calibration would be within ______%
kVp within 10% of the indicted kVp
QC Exposure Timer should be within ____% for exposure times greater than______
within 5% of the indicated time for exposure times greater than 10 ms
QC Linearity should be within _____%
accuracy should be within +/- 10%
QC reproducibility should be within______%
sequential radiation exposures (at least 3) should be within +/- 5%
how does the cathode ray tube work in the digital monitor?
accelerates and focuses electrons to strike the flat plate of fluorescent screen
(scans the screen in lines affecting image quality)
how does the Liquid crystal display work?
passes light through liquid crystals displaying image on the glass faceplate
-electrical signals and light waveforms vary as they pass through the crystals for viewing on the faceplate
