Digital Imaging

Question 1

Digital or Computerized Imaging

Answer 1

the use of a computer to create, improve, or enhance the final image
Exists in soft copy form

Question 2

3 basic types of digital imaging that utilize xrays

Answer 2

Digital or Computed Radiography
Digital Fluoroscopy
Computed Tomography

Question 3

Analog

Answer 3

method of info transmission where results are continuously variable in proportion to intensity of given signal
Is not limited to discrete values
EX: clock

Question 4

Digital

Answer 4

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

Question 5

Analog and Digital Electronic Signals

Answer 5

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

Question 6

Major disadvantage to the electronic tansmission of data in analog form

Answer 6

Signal can become distorted
Causes of distortion include:
inaccuracy when signals are amplified, attenutation losses, electronic noise

Question 7

Example of analog images

Answer 7

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

Question 8

Analog to Digital Convertors (ADC’s)

Answer 8

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)

Question 9

ADC steps

Answer 9

Scanning
Sampling
Digitization/Quantization

Question 10

Scanning

Answer 10

The division of the image into
small regions, forming a matrix,
which is a two-dimensional array
of numbers consisting of
columns and rows.

Question 11

Pixel

Answer 11

a
contraction of picture element
A matrix is made up of many
small squares

Question 12

Field of view (FOV)

Answer 12

The overall dimension of the
image matrix

Question 13

Sampling

Answer 13

Measuring of the strength of an analog signal at different points
More points sampled, the better the representation of signal

Question 14

Concept of aliasing

Answer 14

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

Question 15

Quantization/Digitization

Answer 15

Conversion of the analog sample into a digital signal

Question 16

Image restoration

Answer 16

Used to improve quality of images that have
distortions or degradation (i.e. blurred images can be filtered to make
them sharper)

Question 17

Image enhancement

Answer 17

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.

Question 18

Image analysis

Answer 18

Allows measurements and statistics to be performed as well as image segmentation, feature extraction, and classification of objects

Question 19

Image compression

Answer 19

Reduce the size of the image to decrease transmission time and to reduce storage space
Downside is a loss of spatial resolution

Question 20

Image synthesis

Answer 20

Create images from other images or noimage data
Used in CT and MRI
Looking at blood flow

Question 21

Frequency

Answer 21

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)

Question 22

Contrast

Answer 22

a measure of
the differences between
data values

Question 23

Signal noise

Answer 23

Defined as signal fluctuations that can be caused by internal electronics
Also known as electronic noise
Will degrade image quality and limit visibility

Question 24

Signal to noise ratio

Answer 24

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

Question 25

SNR relationship

Answer 25

Higher noise, lower SNR, lower image contrast
Noisiest component of most digital systems is the display monitor