High pass filter
Passes through high frequency removes low frequency
Low pass filter
Passing through low frequency removes high frequency
Frequency domain
Sorting information according to the sizes of the objects or details
Spatial domain
Sorting information by location in image matrix
Intensity domain
Sorting of the image information strictly by values of the pixels (grey levels)
3 domains
Intensity domain
Spatial domain
Frequency domain
Histogram type 3
Large bolus of positive contrast present (also can compensate for lead shield or prosthesis in FOV)
-Barium studies
Histogram type 2
Body part covers entire detector (no "tail")
-Abdomen
Histogram type 1
With direct exposure present ("tail")
-Extremities
-Over collimation may result in error
Field uniformity
Corrections to even out overall signal and brightness across entire area of imaging field
Post processing
#NAME?
Preprocessing
-All corrections made to "raw" digital image due to flaws in image acquisition that are inherent to the imaging system
-Acquisition processing
-When we first capture image
Quantization
Process of converting a continuous analog signal to a digital signal with discrete numerical values
Aliasing
A result of insufficient sampling of high frequency signals that results in lower frequency signals in the digitized output image
Nyquist theorem
The frequency of an analog signal is faithfully reproduced only if the sampling rate is at least twice that of the maximum signal frequency
The rate of new values is called the _________ or _________ of the converter
Sampling rate or sampling frequency
For image processing image must be digitized
Scanning
Sampling
Quantization
T or F:
Automatic shuttering should never be used to compensate for poor collimation
True
(Ok to remove white background)
Automatic rescaling
#NAME?
T or F
Between histogram and ROI histogram is more advanced
FALSE
What is the application of histograms
Use it to calculate EI number (median)
When machine can't recognize collimation borders
Image gets to light or to dark
Possible outcome of wrong algorithum
ex: Did a pediatric chest with an adult chest algorithum
Contrast will change
What happens when computer starts analyzing histogram
Min
Max
Grey shades
T or F
A histogram is 100% anatomy specific
TRUE
Histogram is a visual representation of arrangement of __________
#NAME?
Window width=
Image contrast (grey scale)
Window level=
Changes brightness
Look up tables
Table with numbers, all the pixels in the image. Shades of grey represents change in contrast
Spatial=
In space
Frequency=
#NAME?
Sampling frequency=
Break down
-How often you are sampling frequency to turn into signal
Modulation transfer function is dependent on
Spatial frequency
T or F
High DQE= higher patient dose (detected (detective) quantum efficiency)
FALSE
Spatial resolution
Sharpness of the image (details)
Bit depth
#NAME?
Why is it important to know your machine
Less likely to overexpose patients
Few images put together=
Stitching
3 domains:
Frequency
Spatial
Intensity
How does ROI work (region of interest)
Takes specific anatomical area (region)
What happens if you don't have high enough sampling frequency
Aliasing (big broad bands over image, wrap around)
(DR) What affects spatial resolution in flat panel detector
Detector element size
Large objects= _________ frequency
Low
Small object= _______ frequency
High
T or F
Sampling frequency affects spatial resolution
TRUE
What affects spatial resolution in CR
Thickness of phosphor layer
Diameter of laser
Sampling frequency
Image manipulation
#NAME?
Image processing
#NAME?
T or F
High DQE can result in lower patient dose
TRUE
Detected (detective) Quantum Efficiency (DQE)
Efficiency of a detector in converting incident x-ray energy into an image signal
Higher SNR=
(signal to noise ration)
More signal overrides noise (GOOD)
Acceptable noise depends on
Viewers sensitivity
Noise level depends on
Exposure
3 causes to image noise
Quantum mottle
Structure mottle
Scatter noise
Unwanted fluctuations in brightness unrelated to object being imaged
Image noise
Contrast resolution is measured through ________
Modulation transfer function (MTF)
Contrast resolution
Ability of a system to image adjacent structures having similar mass density (similar tissue)
Contrast
Degree of difference between the light and dark areas of a radiograph
DR spatial resolution is determined by
DEL size
T or F
Sampling frequency may be specific to receptor size
TRUE
CR spatial resolution determined by
Phosphor layer thickness
Sampling frequency
Laser beam diameter
T or F
Smaller pixels= worse resolution
FALSE
More pixels (larger matrix) = ________ resolution
Smaller pixels= larger matrix= ______ resolution
Better
Better
The most common type of measuring spatial resolution is called the
Spatial frequency
Spatial resolution
#NAME?
The range of gray levels made available to construct the image is called ________
Dynamic range
The number of ______ determines the number of shades of gray the digital system is capable of displaying
Bits
Numerical value of pixel determines its
Brightness
T or F
Size of pixels in an image is directly proportional to the size of the displayed FOV and inversely proportional to the matrix size
TRUE
Matrix size is determined by
Pixel size
-CR; laser diameter, sampling frequency
-DR; DEL size
Receptor size