Image Registration Flashcards
What is contrast resolution?
The ability to image differences among low contrast tissues
What is geometrical accuracy?
The ability to produce an image that is a geometrically correct
representation of the object imaged
What is spatial resolution?
The ability to identify an object as distinct and separate from
another object
What is Sensitivity?
The ability to detect differences in an object
Specificity
The ability to accurately determine the nature of the imaged object
What is a T1 weighted image?
spin-lattice or longitudinal relaxation
time.
Depicts anatomy well (low sensitivity for disease without contrast)
What is a T1 weighted image?
spin-spin or transverse relaxation
time.
Depicts diseases with high water content well (low specificity though)
What is a proton density weighted image?
Depicts anatomy and disease well (currently limited applications).
Higher spatial resolution than T1 and T2.
What is a spin echo (SE) and fast/turbo SE.
INCREASES spatial resolution and reduce artifacts caused by magnetic field and inhomogeneties.
Fast SE is preferred for RT - it is faster and reduces motion artifacts
What is a gradient echo?
Very short acquisition time minimises motion artifacts, DECREASE spatial
resolution; used for multi-phased imaging, oxygenation levels
What is diffusion weighted imaging (DWI)
Differentiating between ↑cellular density (tumours) and ↓cellular
density (benign tissues inflammation necrosis
What is the difference between a T1 and T2 image?
T1 fat is white
T2 fluid is white
What colour is fat in a T2 fast spin echo (FSE) image
Fat is bright
What are MRI limitations?
Image distortion due to non-uniformities
in the magnetic field
Image quality dependence on coils. ( this is a problem for RT imaging requirements e.g. fitting immobilisation under coils.
Poor imaging of cortical bone.
MRI distortion
What common radionucleiode is used for PET scanning?
FDG (fluoro-D-glucose).
What are the limitations of PET?
High uptake in benign pathologies.
Image resolution musch poorer than CT ( difficult to delineate tumour volumes).
PET is a metabolic image
Why does PET have a poor image resolution?
PET uses a relatively large voxel size (0.4x0.4x0.4)
Images appear pixelated compared to CT.
(Difficult to define a geometric edge)
What is semi-automated rigid image registration?
Use of automatic translational functions
to match landmarks and/or surfaces
What is automates rigid image registration?
Use of algorithms to perform matching
based on statistical analysis or signal
processing of the voxel data of the two
image sets
What are the 2 most common algorithms used in automated image registration?
Cross Correlation
Mutual Information
What is cross correlation?
Used for registering an image with similar information.
Best suited to registering intra-modality images (CT-CT or MRI-MRI) registration.
Can be used CT-MRI
What is mutual information?
Used for registering images with dissimilar information.
Technically this algorithm can be used for all multi-modality image registration.
Most commonly used for CT-PET or MRI-PET registration.
