Digital Data Flashcards
Smallest element in a digital image
-discrete values
Pixel
The process of associating the pixels with discrete values
Maximum contrast resolution
What is the size of the pixel directly related to?
Spatial resolution or detail in the image
T/F
Pixel size may change when the size of the matrix or FOV changes
True
The amount of information that can be stored in the pixel (shades of grey that can be represented)
Pixel bit depth
T/F
The number of grey tones that a pixel can produce is 2 to the power of the bit depth
True
See side 7
What is the determining factor for contrast resolution?
Bit depth
What is the bit depth in most digital imaging systems?
10-16
The grey level will be a factor in determining what?
Image contrast resolution
What are the typical matrix sizes?
512x512
1024x1024
2500x2500
What is the relation in matrix and pixel size?
Large matrix - small pixel
Small matrix - large pixel
Area imaged
Field of view (FOV)
The larger the FOV, the more area imaged
T/F
Changes in FOV will not affect matrix size
True
When a field of view gets smaller, what happens to the pixel size, and spatial resolution?
Smaller pixels
Increased spatial resolution
T/F
Changes in matrix size does not affect contrast resolution
True
Pixel bit depth affects contrast resolution
Will changing the matrix size, and or the files of view change the pixel size?
Yes
What is the relationship between pixel size and FOV?
Direct
Increased FOV = increased pixel size
What is the relation between pixel size and matrix size?
Inverse
Increased matrix size = decreased pixel size
The amount of exposure received by the IR
Exposure index
The images appearance on the display monitor of the computer
(The amount of light transmitted by the monitor as well as light reflected off the monitor can affect image appearance)
Brightness
How can brightness be adjusted?
Adjusting window level
Ability of the digital system to display subtle changes in the shade of grey
-directly related to pixel depth
Contrast resolution
How can contrast resolution be adjusted?
Window width
(Control contrast towards a longer or shorter scale)
T/F
If contrast is too low, it can be difficult to separate the image signal from noise and background
True
The ability of the imaging system to demonstrate small details
Spatial resolution
Digital radiography has a higher dynamic range:
-can respond to a wider variety of levels of exposure
-more tissue densities are seen, giving the appearance of more detail
What is related to spatial resolution in computed radiography (PSP systems)?
-Phosphor layer thickness
-pixel size
What is related to spatial resolution in digital radiography?
Pixel size
The ability of a system to record available spatial frequencies
Modulation transfer function (MTF)
What would the MTF of a perfect system be?
1or 100%
Anything that interferes with image formation
Noise
Superimposition of body parts
Anatomic noise
Noise that occurs during image acquisition
Radiographic noise
Noise that occurs from detector elements
Non uniform response
Equipment noise
How much noise can be tolerated in an image
Signal to noise ratio (SNR)
As SNR increases, noise decreases
*different detectors will require different amounts of exposure to achieve the same SNR
Range of exposure diagnostic image values the IR is able to produce
Exposure latitude
Increased dynamic range = more values can be detected
How efficiently a system converts the xray input signal into a useful output image
A measurement of the percentage of X-rays absorbed when they hit the detector
Detective quantum efficiency
What are some examples of analog?
-paintings
-printed photographs
-continuous images
What are some examples of digital?
-numeric values
-array of small elements
Xray converted to light, and the light waves are recorded as single intensities
Analog
Analog signals are converted to number to be recorded
Digital images formed through multiple samplings of the signal
Digital
When does analog to digital conversion occur in imaging?
-CR reader
-digital imaging
-film digitizers
What are the 3 steps in analog to digital conversion? (ADC)
Sampling
Quantification
Binary coding
The analog voltage values are measured at a chosen sampling frequency on the analog waveform
ADC: sampling
Each sampled piece of analog data is the computed and assigned a discrete analog value
ADC: quantificstion
Sampled values are converted to a binary digit (bit)
Binary coding
When sampling a signal, the sampling frequency must be greater than twice the frequency of the input signal so that the reconstruction of the original image will be as close to the original signal as possible
Nyquist theorem
Results in a wraparound image, which appears a two superimposed images that are slightly out of alignment, resulting in a moire effect
Aliasing
