Resolution Flashcards
Regarding ultrasound, what is the definition of resolution?
The ability to distinguish objects as separate, or two echoes, not one all lumped together. It provides definition between small structures.
What is axial resolution?
The ability of the system to display two structures that are very close together, parallel to the sound beams main axis, as individual structures.
Axial is just one form of detail found in an image.
What are some synonyms for axial resolution?
Longitudinal, Radial, range of depth.
What is a major factor affecting axial resolution?
Spatial pulse length has the biggest influence on axial resolution. A shorter pulse can get between closely spaced reflectors.
What are two ways to create A small spatial pulse length?
Provide less ringing, which is helped by the backing material.
Use a higher frequency.
In the axial dimension, what is the closest two objects can be along the beam direction and still be resolved as two distinct echoes?
One half SPL.
How do you determine SPL?
How do you determine one half SPL?
SPL = number of cycles x wavelength of one cycle
SPL = number of cycles x wavelength of one cycle / 2
What is the definition of lateral resolution?
The ability to distinctly identify two structures that are very close together, side-by-side, perpendicular to the sound beams main axis.
What is the minimum distance two structures can be positioned, side-by-side, and still produce two distinct echoes.
This is determined by the width of the sound beam. The beamwidth has the biggest influence on lateral resolution. And narrower beam can get between closely spaced reflectors.
How is high frequency an advantage to resolution?
High-frequency provides better axial resolution because the shorter SPL comes from a shorter wavelength
Better lateral resolution comes from higher frequency because there is less divergence of the game in the far field so ultimately it provides a narrower beam.
Where is lateral resolution?
best lateral resolution is best at the focus/ focal point
Lateral resolution = Beam diameter
What is temporal resolution?
The ability to accurately determine position of an anatomical structure at a particular instant in time.
What is another way to describe temporal resolution?
The number of image updates per unit time. Frame rate per second.
What determines better temporal resolution or worse temporal resolution?
A faster frame rate is better temporal resolution, in his lower frame rate is worse temporal resolution.
What are factors that affect Frame rate?
The amount of processing time needed to produce image updates.
EssentiallyTwo categories: Imaging depth and number of pulses per image update.
