Digital Imaging Flashcards
Digital or Computerized Imaging
the use of a computer to create, improve, or enhance the final image
Exists in soft copy form
3 basic types of digital imaging that utilize xrays
Digital or Computed Radiography
Digital Fluoroscopy
Computed Tomography
Analog
method of info transmission where results are continuously variable in proportion to intensity of given signal
Is not limited to discrete values
EX: clock
Digital
Method of info transmission where the signal varies in discrete steps and not in continuous manner
More precise and easier to read
EX: numbers and values are displayed as in a digital clock
Analog and Digital Electronic Signals
analog and digital can also describe types of electronic signals that carry data
Analog signals continuously vary in strength
Digital signals vary in specific values of current and voltage
Major disadvantage to the electronic tansmission of data in analog form
Signal can become distorted
Causes of distortion include:
inaccuracy when signals are amplified, attenutation losses, electronic noise
Example of analog images
Conventional film/screen, fluoroscopic
images made with tube-type
image intensifiers
represents a continuous
distribution of light intensity as a
function of position on the
radiograph
Analog to Digital Convertors (ADC’s)
If an analog electronic signal
needs to be processed by a
computer, it must be converted
into a digital form by an analog
to digital convertor (ADC)
ADC steps
Scanning
Sampling
Digitization/Quantization
Scanning
The division of the image into
small regions, forming a matrix,
which is a two-dimensional array
of numbers consisting of
columns and rows.
Pixel
a
contraction of picture element
A matrix is made up of many
small squares
Field of view (FOV)
The overall dimension of the
image matrix
Sampling
Measuring of the strength of an analog signal at different points
More points sampled, the better the representation of signal
Concept of aliasing
If an insufficient number of samples are taken, the representation of original signal will not be accurate after computer processing
Causes moire pattern artifacts in the image
Quantization/Digitization
Conversion of the analog sample into a digital signal
Image restoration
Used to improve quality of images that have
distortions or degradation (i.e. blurred images can be filtered to make
them sharper)
Image enhancement
The purpose of this class of processing is to generate an image that is
more pleasing to the observer.
Certain characteristics such as contours and shapes can be enhanced to
improve the overall quality of the image.
The operations include contrast enhancement, edge enhancement,
spatial and frequency filtering, image combining, and noise reduction.
Image analysis
Allows measurements and statistics to be performed as well as image segmentation, feature extraction, and classification of objects
Image compression
Reduce the size of the image to decrease transmission time and to reduce storage space
Downside is a loss of spatial resolution
Image synthesis
Create images from other images or noimage data
Used in CT and MRI
Looking at blood flow
Frequency
The amount of
raw data applied to create the
digital image, and determines
the frequency of the electric
signal, and sometimes
referred to as bandwidth
(expressed in bits per second)
Contrast
a measure of
the differences between
data values
Signal noise
Defined as signal fluctuations that can be caused by internal electronics
Also known as electronic noise
Will degrade image quality and limit visibility
Signal to noise ratio
Amount of signal noise is measured by this
SNR=Signal/noise
High SNR indicates a low amount of noise in the image
Effect of noise is similar to film grain and base + fog in image
SNR relationship
Higher noise, lower SNR, lower image contrast
Noisiest component of most digital systems is the display monitor
