crdr 7 Flashcards
What step of image processing that occurs prior to the image being displayed where the algorithms determine the image histogram, detector defects are removed, and noise corrections are performed?
pre-processing
What step of image processing that is done by the technologist to prepare the image for the radiologist through various user functions?
post-processing
It is the graphic representation of densities produced by the data within the collimated area.
histogram
What is the meaning in histogram if it represents black areas?
it acquired greater signal
What is the meaning in histogram if it represents white areas?
it did not acquired any signal
How does kVp affect the histogram?
Low kVp – wider histogram
High kVp – narrower histogram
What is the theory stating that the sampling rate must be at least twice the highest frequency to accurately reconstruct the original signal?
Nyquist theorem
He described a way to convert analog signals into digital signals that would more accurately transmit over telephone lines.
Harry Nyquist (1928)
He presented a mathematical proof of Nyquist’s theory, allowing it to be called the Nyquist theorem.
Claude Shannon (1948)
What happens when the sampling rate is below the Nyquist frequency?
ALIASING occurs, causing loss of information and a fluctuating signal, resulting in a wraparound image (moiré effect).
Aliasing is also known as..
fold-over or biasing
What is a process ensuring images have uniform brightness and contrast, regardless of exposure level?
automatic rescaling
What happens with incorrect exposure?
Too little exposure – results in quantum mottle
Too much exposure – results in loss of contrast and loss of distinct edges
What is a histogram used to correct luminance values by mapping pixel values to new gray values for proper image display?
look-up table (LUT)
The initial digital image appears ____ when graphed because all shades of gray are visible, giving the image a very wide latitude
linear (straight lines)
What are different contrast enhancement parameters used by vendors?
Agfa – uses MUSICA;
Fujifilm – uses Gradation;
Carestream – uses Tonescaling
This involves converting the digital input data to an image with appropriate brightness and contrast using contrast enhancement parameters
contrast manipulation
What is the measure of image sharpness or detail, in line pairs per millimeter (lp/mm), influenced by focal spot and object-to-image distance (OID)?
spatial frequency resolution
ung box about spatial resolution, TINGNE SA MODULE reviewhe
What are the two types of spatial frequency filtering?
- Edge enhancement
- Smoothing
What is the type of spatial frequency filtering that is also known as high-pass filtering and occurs when fewer pixels in the signal average to enhance edges. Smaller neighborhoods increase enhancement.
edge enhancement
What is a type of spatial frequency filtering that is also known as low-pass filtering that occurs by averaging each pixel’s frequency with surrounding pixel values to remove high-frequency noise. Useful for reviewing small structures such as fine bone tissues
smoothing
What is masking in edge enhancement?
Suppressing frequencies, which can result in the loss of small details
This controls how bright or dark the screen image is.
window level
