Lesson 18 (Part 1) Flashcards
Resolution (2)
- To create a better picture
2. Being able to separate distinct echoes
What are 3 examples imaging resolution?
- Detail/spatial
- transducer - Contrast
- instrument - Temporal
- instrument
What kind of resolution is better?
Smaller
- tinier details can be discerned
What happens if 2 reflectors are not separated sufficiently?
They produce overlapping echoes
- smear
What is axial resolution also known as? (4)
- Longitudinal
- Radial
- Depth
- Range
Axial resolution
Minimum reflector separation along scan lines to produce separate echoes
What happens to the image when distance between the structures is greater than the axial resolution?
It will appear as a single structure
- smear
What happens to the image when the distance between the structures is lower than the axial resolution?
You will get separate structures
What is the formula for axial resolution?
AR = SPL/2
- AR = axial resolution
- SPL - spatial pulse length
How do you get the best axial resolution?
Smaller SPL
What is the unit for axial resolution?
mm
How do we reduce SPL? (3)
- Reducing the number of cycles
- Reducing the wavelength
- Increase frequency
How do you reduce the number of cycles?
Applying damping
What does increasing frequency affect?
Penetration
What is lateral resolution also known as? (3)
- Angular
- Transverse
- Azimuthal
Lateral resolution
Minimum reflector separation perpendicular to scan line to produce separate echoes
- horizontal line
What is the formula for lateral resolution?
LR = Wb
- LR = lateral resolution
- Wb = width of beam
What is the unit for lateral resolution?
mm
What happens in lateral resolution of the resolution is too high?
You get a smearing effect
What happens if the beam is narrower than reflector separation in lateral resolution?
You get 2 distinct structures
What is the lateral resolution at the focus?
Same as what is the beam width at the focus
What is the formula for beam width?
1/2 of the aperture
What is the best lateral resolution?
The smaller the better
How is lateral resolution improved?
By reducing beam width
How can you reduce the beam width in lateral resolution?
By adjusting the focus
- making it more narrower
Where can you move the focus?
Near zone length
- NZL
Where cant you move the focus?
Far zone length
What can you change in the FZL?
Aperture size
