3. Image Reconstruction and Display Flashcards
Name the 4 things that affect the absorption of radiation within the patient
- Energy
- Patient thickness
- Atomic number
- Tissue density
What determines the grey shades in the images
CT numbers
Which is the best choice for a supine pelvis simulation?
Confirm bladder and bowel prep, hands on chest, pillow and legs immobilized
What CT artifact occurs due to malfunctioning detector?
Ring artifact
What are the two main reasons for using a scout/pilot/topogram image?
- To set scan borders for a CT simulation
- Verify patient is straight
What is the CT scan technique that separates the different respiratory phases?
Retrospective
During an abdomen, CT simulation, where do you place the BB spots?
Right, left, and anterior
What is the use of power injectors in the CT simulator?
Inject iodinated contrast to vessels
What is needed to acquire a helical CT scan?
Continuous couch and x-ray motion
What is reconstruction?
The creation of the image and use of filters
NB: They are functions done on the raw data set
What is a ray?
The path that the x-ray beam takes from the tube to a single detector
What is Ray sum?
The attenuation along a ray
What is a view?
A complete set of ray sums
What is attenuation profile?
The system that accounts for the attenuation properties of each ray sum and correlates it to the position of the ray
What are algorithms?
Finite set of unambiguous steps performed in a prescribed sequence to solve a problem
What is Fourier transform?
An image-processing tool that decomposes an image into its frequency components
What is interpolation?
A mathematical method of estimating the value of an unknown function using the known neighbouring values
What is convolution?
Applying a filter function to the attenuation profile
T or F. Filtering can only be applied to raw data
True
What is Reformation (image rendering)?
When IMAGE DATA are assembled to produce images in different planes or to produce 3D images
What is Multiplanar Reformation?
These are 2D displays which always represent the original CT attenuation values
What is curved planar reformation?
This is created along the center line of tubular organs
What is three-dimensional reformation?
This seeks to represent the entire scan volume in only one image
Name 4 types of 3D reformation
- Surface rendering (SR)
- Projection displays (MIP and MinIP)
- Volume rendering
- Endoluminal imaging
What is volume rendering?
A three-dimensional semi-transparent representation of the imaged structure
What is endoluminal imaging?
A type of VR that is designed to look inside the lumen of a structure.
NB: aka perspective volume rendering or virtual endoscopy
What is 3D modeling?
This is when 3D printers produce 3D models using CT data sets (volume rendering)
NB: can be used for treatment planning and to create bolus
What is region-of-interest editing or segmentation?
This is done to remove obscuring structures from the 3D image
Name the factors that degrade reformatted images
- Segmentation errors
- Image noise
- Artifact (motion, metal, stair-step)
NB: Stair-step is when thick slices are used for reformatting
The process of convolution to the raw data is an example of:
Reconstruction
Where is image center defined in the CT simulator?
Scan field of view
Applying a filter to the raw CT data is an example of:
Reconstruction
With MIP, what does the viewer see along a single viewing path?
The brightest voxels
What is the purpose of a MIP CT in radiation therapy?
To view a tumour throughout the respiratory cycle
Name 3 things that reformation can be used for.
- Improved tumour tracking
- Creation of bolus for RT
- Viewing the inside of the colon
What is the main difference between reconstruction filters and windowing?
WF is the foundation of the data that is used to create the image (it is permanent) but windowing is how the image is visualized (it is not permanent)
