Wk07 Image Guided RT Flashcards
What is the definition of image registration
The process of determining the geometric transformation that relates identical points in two image series: a moving dataset (study A) and a stationary source dataset (Study B)
What is the definition of image fusion?
The combined display of the mapped date from the moving dataset with the stationary dataset.
What are the 3 common ways of image transformation?
- Rigid transformation
- translations and rotations - Affine transformation
- rigid transformation + scaling and sheering - Deformable registration
- objects are deformed, translated and rotated to match both images
What are the application of deformable registration?
- Correct difference between MR and CT flexion angle of cervical spine
- Deform contours for adaptive radiotherapy
What should be aware when perform deformable registration?
- carefully select the ROI, especially when the scan range are different
- deformable registration should not be performed for post-op cases or cases with bolus
- care should taken on images with substantially different tumour sizes.
Name 2 automatic registration algorithms
- Intensity-based
- Geometry-based
Due to vastly different intensity pattern, ___________________ is useful in multi-modality image registration.
Mutual information
Daily imaging can reduce _____________________error, regular imaging can reduce __________________error.
Systematic and random ; systematic
What are the special features of a CT simulator compared to a normal diagnostic CT?
- a big bore to cater treatment positions
- laser system
- accurate CT numbers for dose calculations
- flat couch top
What report guide the QA of CT simulators?
Report NO. 083 (AAPM)
CT simulators need regular QA on:
- geometrical accuracy of images
- accuracy of CT numbers
- accuracy of CT lasers
- Image quality (noise, contrast, resolution)
- accuracy of table motion
MR simulation can replace CT simulation if MR simulation can?
- can be used for delineation of all OARs and targets accurately
- can be used for radiation dose calculation
- can simulate treatment position accurately
What are the features of a MR simulator?
- large bore size
- laser system
- flat couch top
- special receiver coils and accessories dedicated for RT simulation
- dedicated pulse sequence —> to generate density map for dose calculations
_______________ mimic simulation CT for dose calculation and _________________ for setup verification.
synthetic CT ; generate DRR
What report or guidelines control the QA for MR simulation?
AAPM task group 284: MRI simulation in RT
AAPM report No.100: acceptance and QA for MRI
During MRI QA, physicist need to ensure:
- geometrical accuracy of images
- accuracy of synthetic CT numbers
- accuracy of simulation lasers
- appropriate zoning
- fringe fields
- integrity of RF shielding
- image quality
- accuracy of table motion
What phantom is used for MRI QA?
ACR phantom
What are the definition of different MRI zones? (Zone 1-4)
Zone 1: areas that are freely accessible to the general public
Zone 2: interface between publicly accessible and controlled area (eg. Px waiting area)
Zone 3: area which personnel or ferromagnetic equipment can result in serious injury or death (eg. Control room)
Zone 4: the MR scanner room itself
What is the definition of MR safe, MR unsafe and MR conditional?
MR safe = an item poses no known hazards in all MR environments
MR unsafe = an item is known pose hazards in all MR environment
MR conditional = an item pose no known hazards in specified MR environments with specified conditions of use. (Eg. An item is safe near a 1.5T magnet, but not for 3.0T)
Pacemaker may be affected by magnetic field exceeding ______________.
5 gauss
What is the earth magnetic field?
0.5G
What are the 2 functions of radiofrequency (RF) shielding?
- To prevent extraneous electromagnetic radiation from contaminating or distorting the MR signal
- To prevent electromagnetic radiation generated by the scanner from causing interference to nearby medical devices
What is ray tracing in constructing DRR?
Tracing ray lines from a virtual source position through the CT date of the patient t a virtual film plane
What are the difference between CBCT images and normal CT images?
- CBCT have higher noise level due to increase amount of scatter received
- CBCT are more susceptible to patient motion due to longer acquisition time
- Limited field of view (FOV)
