Imaging Resolution Flashcards
Sector transducers are good at creating better resolution. What type of resolution is this?
Temporal resolution
How to improve axial resolution?
- Increased frequency - decreases wavelength
- Dampening material on transducer (less ringing and listening which decreases SPL)
- Shorter SPL
What is the formula for axial resolution?
SPL/2
If SPL is 12mm, will structures that are 7mm apart be distinguished separately?
AR must be equal or greater than the SPL/2.
12mm/2 = 6mm, so structures MUST be at least 6mm or greater apart to be seen as separate
If SPL is 12mm, will structures 4mm apart be distinguished separately?
NO, since the formula is 12mm/2 = 6mm, structures less than 6mm apart will not be distinguished separately
Lateral resolution is equal to what?
The beam width
How to improve lateral resolution?
Focusing - the best LR is at or just before the focus
What does multiple foci do to lateral resolution and temporal resolution?
Improves lateral resolution
Decreases temporal resolution
Where is the best lateral resolution?
At or just BEFORE the focus
How do you change the focus to improve lateral resolution?
- Changing the aperture (number of crystals)
- Phasing
Where should you place the focus to improve lateral resolution?
At or just BELOW the area of interest
Where is the highest intensity of the beam?
At or just before the focus
What is the elevational plane also known as?
The slice thickness plane
What artifact is seen in the elevational plane?
Slice thickness/partial volume artifact
What is elevational resolution dependent on?
- Lens
- Size and shape of the crystal
How to improve elevational resolution?
Harmonics
What types of resolution is improved with harmonics?
Lateral and elevational
What type of artifact creates a “filling in” of anechoic structures to become more echoic?
Slice thickness artifact/partial volume
Does slice thickness artifact occur when the slice thickness is larger or smaller than the size of the structure?
Larger
What type of resolution has the ability to display and differentiate structures based on varying levels of brightness?
Contrast resolution
How many shades of grey are on ultrasound imaging?
How can contrast resolution be changed by the sonographer?
- Gains
- TGC’s
- Compression
- Dynamic Range
How do you change the number of shades of grey on ultrasound?
Dynamic range buttom
What gives the best contrast resolution based on dynamic range and compression?
Decreased dynamic range and increased compression
Will increasing the dynamic range improve or degrade contrast resolution?
Degrades
What resolution is based on the image constantly changing due to the motion of structures?
Temporal resolution
What is temporal resolution dependent on?
- Frame rate/ lines per frame
- Depth of the beam
- Sector width
- Multiple focuses
What is temporal resolution highly dependent on?
Frame rate
How to IMPROVE temporal resolution?
- Decreased depth
- Decreased sector width
- Decreased scan lines
What happens to the frame rate when you increased the frequency?
Increase FR
When is multiple foci helpful?
In static imaging, especially for breast and liver
