CT For RT Flashcards
1
Q
What is the role of CT in RT?
A
- provide 3D and 4D CT data for RT treatment planning and calculations
- creation of DRR (digital reconstructed image)
2
Q
What is the basic overall process of CT?
A
- attenuation of beam occurs as x-ray pass through patient, absorption and scatter
3
Q
What is the difference between single and multi slice CT?
A
- single is one detector
- multi is 16+ detectors
4
Q
What is a scout image?
A
- standard area protection image with relevant anatomical structures visualised and localised relative to table
- provide references for CT scan
5
Q
What are CT numbers/hounsfield units?
A
- numbers used to define relative attenuation coefficients for each pixel of tissue in an image as compared to the attenuation coefficient of water
- CT number correlates to a grey scale
6
Q
What is helical scanning?
A
- high image quality in helical made when pitch = 1
7
Q
How does pitch effect image quality?
A
- image quality decreases as the pitch increases
- more noise as pitch increases as fewer pieces of information are used
- patient does decreases as pitch increases
8
Q
What causes metal artifacts?
A
- due to the beam being absorbed almost entirely by metal
- metal artifact reeducation sequence (MARS) can be used to optimise decision of metal artifacts
9
Q
What causes a motion artifacts?
A
- voluntary and involuntary including breathing
- appear as streaks
- proper instructions to patients
- short scan times can decrease artifacts
10
Q
What affects image quality?
A
- mAs, kV, FOV, slice thickness and pitch
11
Q
What is image windowing?
A
- windowing to create the most optimal display for viewing particular regions of anatomy
- window width: determines upper and lower range of CT number to be viewed
12
Q
What is the patient positioning and imbolisation?
A
- immobilise to be comfortable, stable and reproducible
- constraints on devices that need to fit into the machine and don’t produce artifacts
