CT Image Reconstruction
Selecting what will determine how much of the raw data is used to create an image?
Display field of view (DFOV)
Which is an example of a computer input device? a. microprocessor b. primary memory c. CT detector mechanisms d. laser camera
c. CT detector mechanisms
The ______________ interprets computer program instructions and sequences tasks.
central processing unit (CPU)
The process of applying a filter function to an attenuation profile is called _____________
convolution
What is the portion of the computer that can be physically touched?
hardware
What is the process of manipulating the data so as to produce a useful image that can be sent to a display device called in CT?
image reconstruction
What is a mathematical method of estimating the value of an unknown value using the known values on either side of the unknown value?
interpolation
What are the 3 principal types of computer memory?
1. Read-only memory (ROM) 2. Random Access memory (RAM) 3. Write-Once, Read-Many (WORM)
What are the 4 principal components of a computer?
1. input device 2. output device 3. central processing unit 4. memory
The CPU is made up of what 3 things?
1. microprocessor 2. control unit 3. primary memory
Changing the ________ will affect image quality by changing the amount of raw data that is averaged together for each pixel
DFOV
T/F: Only one view is needed to create an image.
False! MANY views are needed to create an image
T/F: Image data require much more computer storage than that of raw data.
False! RAW data requires more storage than IMAGE data
______ devices feed data into the computer - give examples
INPUT devices include: keyboard, mouse, touch-sensitive plasma screen, and CT detector mechanisms
To form an image, the computer assigns how many HU values to each pixel?
ONE HU per pixel
________ devices accept processed data from the computer - give examples
OUTPUT devices include: monitor, laser camera, printer, and archiving equipment (servers, optical disks, or magnetic tape)
What can occur if any part of the patient lies outside of the SFOV?
Out-of-field artifacts
What two names refer to the data sitting in the computer waiting to be made into an image?
Raw data or Scan data
___________ are used in CT to convert information obtained from the detector array into information suitable for image display.
Reconstruction algorithms
What is it called when the same raw data are used later to generate a new image?
Retrospective reconstruction
What determines the number of detector cells collecting data?
SFOV selection
What is the opposite of RAM memory?
Serial Access memory (SAM)
T/F: An attenuation profile is created for each view in the scan.
True
T/F: An enormous amount of information is collected for each image.
True
T/F: Fast Fourier transform (FFT) is an efficient algorithm that is used in image analysis and many other applications.
True
Increasing the scan field of view a. increases the number of detector cells collecting data b. increases the range of HU displayed on the image c. decreases the pixel size d. decreases the display field of view
a. increases the number of detector cells collecting data
What is a precise set of steps to be performed in a specific order to solve a problem??
an algorithm
Saving data on auxiliary devices for possible future viewing is referred to as ________________
archiving
The system accounts for the attenuation properties of each ray sum and correlates them with the position of the ray. The result of this correlation is called a(n) _____________
attenuation profile
The process of applying a filter function to an attenuation profile is known as: a. data processing b. convolution c. archiving d. reformation
b. convolution
The process of converting the data from the attenuation profile to a matrix is known as ____________
back projection
Raw data includes all measurements obtained from the ___________
detector array
___________ is done to minimize artifacts that can occur during the back projection process
filtering
Regardless of what size of SFOV is selected, or where the patient is positioned within the gantry, scan data are always collected around the ___________
isocenter
What is the simplest type of interpolation?
linear interpolation
What does linear interpolation assume?
linear interpolation assumes that an unknown point falls along a straight line between two known points
The information from all of the attenuation profiles is projected onto a __________.
matrix
What is WORM memory?
memory that does not allow saved information to be rewritten, reformatted, or erased
What is SAM memory?
memory that stores data that can only be accessed sequentially
What is RAM memory?
primary memory includes instructions that are frequently changed, such as the data used to reconstruct images - named because all parts of it can be reached easily at random
What is ROM memory?
primary memory that is imprinted at the factory that is used to store frequently used instructions such as those required for starting the system
Image reconstruction that is automatically produced during scanning is called what?
prospective reconstruction
The path that the x-ray beam takes from the tube to the detector is referred to as a _________
ray
The detector reads each arriving ray and measures how much of the beam is attenuated. This measurement is called a _________
ray sum
____________ determines the area, within the gantry, from which the raw data are acquired.
scan field of view (SFOV)
What is instructions that tell the computer what to do and when to do it?
software
What is image data?
the data that result once the computer has processed the raw data and displayed an image
A complete set of ray sums is known as a _______
view