CT Image Quality Flashcards
Define spatial resolution.
the ability of a CT system to display fine details separately; the degree to which a CT system can distinguish very small parts
Define MTF. What is its range?
modular transfer function. used to show accurately a CT system can display an object. an MTF of 1.0 is 100% to scale, while an MTF of 0.0 does not show the object
A small focal spot ________ spacial resolution.
increases/improves
How can detector size and geometry affect spacial resolution?
smaller, closely spaced detectors IMPROVE spacial resolution
High frequency reconstruction algorithms (kernels) are used for what type of anatomy? How would this kernel affect spacial resolution?
- bones, or edges (of anatomy)
2. improve spacial resolution
What combination of large/small matrix size and large/small pixels/DFOV gives the best spacial resolution?
large matrix size and small pixels (small DFOV)
What element affects longitudinal spacial resolution? How is LS resolution measured?
how quickly the patient moves through the gantry (pitch). it is measured by the slice sensitivity profile
By increasing pitch, you ______ longitudinal spacial resolution.
decrease
Define contrast resolution.
the ability of a CT system to differentiate two objects with very similar densities, or linear attenuation coefficients
What is the smallest difference, in HU, a modern CT system can differentiate?
3 HU
A decrease in noise results in a(n) _______ of contrast resolution.
increase
What algorithm results in increased contrast resolution?
low frequency
Increasing detector collimation _______ contrast resolution.
decreases: this will increase noise which reduces contrast
Define temporal resolution.
the ability of a CT system to “freeze” motion
What is the main factor controlling temporal resolution?
the speed of the gantry rotation
