CT Image Reconstruction

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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


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