Week 6 - Pre Processing Flashcards
The study of the relationship between intensity of exposure of the film and the blackness after processing
-displayed as graphic relationship between exposure and density of the film
Sensitometry
The graphic relation between optical density (OD) and radiation exposure
Characteristic curve
-of a radiographic screen film image receptor
T/F
The response of a digital IR to xray exposure is linear
*increased exposure latitude
True
T/F
Digital detectors do not have a Dmax
True
The range of exposures that produce densities in the diagnostically useful range
Exposure latitude
*with wider latitude, mAs can vary more and still produce a diagnostic image
Functions analyze and adjust acquired raw data for image creation
-histogram analysis
-lookup table adjustments
-automatic rescaling
Pre processing
Functions aid in adjusting the appearance of the pre processed image data
-brightness (WL)
-contrast (WW)
-masking
-edge enhancements
Post processing
Amount of exposure signal
X axis
Number of pixels for each exposure
Y axis
What type of histogram does a low kVp create?
Wider histogram
-high contrast
-increased variation in signal intensities
What type of histogram does a high kVp create?
Narrow histogram
-low contrast
-decreased variation in signal intensities
T/F
The shape of the histogram is specific to the anatomy images
True
*fairly consistent for same body part images on different patients
Why is it important to choose the correct anatomical region for the exam?
Raw data used to form the histogram are compared with a “normal” histogram of the same body part
Program that searches for recorded anatomy within the collimation edges
-eliminates scatter outside of the desired FOV
Data recognition
What will the resultant image be if the system fails to find the collimated edges?
-incorrect digital data collection
-images may be too bright or too dark
Why is proper centering so important?
Ensures that the appropriate recorded densities will be located
Applied to adjust brightness and contrast after the histogram is applied to the input from the IR
Look up table
Used as a reference to evaluate the raw information and correct the luminance value
Look up table
T/F
Digital IRs have a linear exposure response and a very wide dynamic range
True
-raw data images exhibit low contrast and must be altered to improve the visibility of anatomic structures
Refers to the use of automatic rescaling without regard to appropriate exposure amount
Dose creep
*to combat dose creep, all MRTs should use standardized technique charts
What is data clipping?
The CR system not sending all acquired data by the IR to the post acquisition system because the quantity of data is far greater than the display system can provide for viewing
Data clipping
T/F
Software processing the data is programmed to recognize that some data represents exposure below diagnostic range and some data represents exposure above diagnostic range
True
What are the two types of compression techniques?
Lossless
Lossy
An image file that is compressed and can be reconstructed to be exactly the same as the original image
-no loss of any information of the image when image is decompressed
Lossless compression
*detail is not compromised
How much does lossless compression reduce data file size?
Reduces data file size to 10-50% of the original file size
*for larger image files, this can lead to long transmission time and data manipulation times (not always satisfactory)
T/F
Lossless compression will not lead to a decrease in image quality or detail upon compression
True
A compressed image file that will have some loss of image detail when the image is decompressed
Lossy compression
*can provide compression factors of up to 100:1 or greater
T/F
Lossy compression is not ideal in medical imaging, as loss of resolution can be detrimental to an image
True
PNG
RAW
BMP
Lossless image formats
JPG
Lossy image formats
What percent of its original file size can lossy compression compress a file to?
2-10%
*such a level of compression supports teleradiology but not computer-aided detection (CAD) or image archiving
*may cause CAD system to miss lesions due to compression artifacts
What is considered a compression artifact?
Lack of data
The element that reduces the size of the image file
Compression ratio
Lossless compression methods yield compression ratios of:
2:1 - 3:1
Lossy compression methods yield compression ratios of:
10:1 - 50:1
As the compression ratio increases…
- less storage space required
- faster transmission speeds
- image quality degradation
At what compression ratio is the loss of image quality still visually acceptable?
Low compression ratios
8:1 or less
The maximum compression in which the decompression image is acceptable for interpretation and aesthetics
Compression tolerance
T/F
Radiologists do not use lossy compression algorithms in primary diagnosis
True (high compression ratios)
