Ch. 20 - Digital Image Processing Flashcards
Describe the various types of digital imaging systems (CR &DR)?
- Computed Radiography (CR & DR)
a. Photostimulable imaging plates (PSP, IP) - Digial Radiography (DR)
a. direct conversion w/o scintillator (phosphor substance that emits fluorrescence when exposed to radiation such as x-rays and gamma rays)
b. DR Receptors referred to as flat panel detectors (panels)
Describe ethe process of digital image data formation
a. converted into numerical values for transmission or processing
b. electrical signals from receptors in an analog format
c. must be converted to digial language
- analog -to-digital conversion (ADC)
-requires binary machine lagnuage (0 and 1); 8 bits = 1 byte
describe the ADC (analog to digital conversion)
a. ADC 8involves two distinct steps
- sampling
-quantification
what are the digital image characteristics?
a. matrix
-made up of pixels and voxels; spatial resolution dependent on matrix size
b.pixel
- picture element
-pixel contains a bit-depth (determines # of assigned gray shades to piexe value; greater bit depth yields range of gray shades
-grayscale bit depth ranges from 8 to 32 bits
c. voxel
- volume element (pixel in 3d form)
d. pixel pitch and size
-sampling frequency expressed as pixels/mm
e. pixel bit depth
-determines # of density value
j. image file size
k. spatial domains
- spatial frequency is usually described as the resolution and contrast
Explain 1 of 3 type of digital imaging processing operations (point processing)?
Are those that are performed between the receipt of the input image from the image receptor and the output image that is viewed on the monitor.
-grayscale processing (adjustments to image brightness and contrast)
- creation of a histogram and the application of the look-up table (LUT) and windowing
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Explain 1 of 3 type of digital imaging processing operations (local processing)?
Also called: (area or group processing)
-ex: spatial (location frequency)
-high-pass filtering - edge enhancement
-low- pass filtering - smoothing and blurring out noise
Explain 1 of 3 type of digital imaging processing operations (geometric processing)?
Used to change the position or orientation of pixels in image
-rotation
-magnification
Describe the process by which the histogram is acquired and the look-up table (LUT) is applied to the collected data
- histogram is generated
- Analysis of histogram
-Volume of interest (VOI) - Application of the look-up table
- Windowing for contrast and brightness
How is the Look-up table (LUT) used?
a. LUT is applied to the data and is used to adjust the contrast
b. Not to be confused with windowing/ level (W/L)
c. Can enhance pathologies
( re-mapping grey-scale values in image to a new range4improvement)
What is the function of digital image window level and width controls?
a. used in digital imaging to adjust the brightness and contrast of an image
- WL: Increasing the makes image darker, while decreasing makes brighter
- WW: Increasing reduces display contrast, while decreasing the WW increases the brightness interval between two consecutive pixel values
What are the factors that affect digital image quality?
a. Spatial resolution ( the ability of an imaging modality to differentiate two adjacent structures as being distinct from one another) (blurriness)
b. Density resolution (The amount of darkness in the radiographic image)
c. Contrast resolution (differentiate between different densities in a radiographic image)
d. noise
how can exposure indicators be used as a quality control tool for image quality and radiation protection?
Exposure indicators reflect the amt of x-rays exposure to an image receptor, which looks at the quantity of photons that strike the detector. Therefore, exposure indicators numbers can be used as a quality control tool for image quality and radiation protection. This ensures compliance of ALARA
