Lesson 18 (Part 2) Flashcards
Elevation resolution
Minimum reflector separation perpendicular to scan plane to produce separate echoes
- 3rd dimension
What does the beam have in elevation resolution?
Section thickness / elevational plane
What can elevation resolution produce?
A section thickness artifact
What is a section thickness artifact also known as?
Partial volume artifact
What do partial volume artifacts fill? (4)
- Cysts
- Gallbladder
- Vessels
- Bladder
- anechoic structures
What will poor elevational resolution show?
Echoes from outside the intended scan plane
- especially within anechoic structures
How do we fix elevational resolution artifacts? (2)
- THI
- harmonics - Spatial compounding
What THI is better for fixing elevation resolution artifacts?
Narrower and thinner beam
Why are narrower and thinner beams better for THI?
Less likely to pick up echoes from other planes
Spatial compounding
Scanning at different angles help to deal with anechoic structures
Temporal resolution
Being able to separate echoes in time
How is poor temporal resolution visualized?
As a lag
Contrast resolution
Being able to separate 2 different shades of grey
Is having more shades of gray better or worse in contrast resolution?
Better
What is the useful frequency range for diagnostic applications?
2-20 MHz
What do higher frequencies do? (2)
- Increase resolution
2. Decrease the maximum imaging depth
What happens if you have less than 2MHz?
You are losing resolution/image quality
What happens if you have more than 20MHz?
You will not penetrate as well
How can focus be achieved?
In 3D (perpendicular to the scanning plane) with a lens or curved elements
What does phasing need to be applied to focus the 3D electronically?
At least 3 rows of elements
What does electronic focusing eliminates?
The need for the lens or curved elements
What is 3D imaging?
Volume imaging
What is the down side of 3D compared to 2D?
It lags
What do 2D arrays have the ability to do?
Steer and focus in 2 dimensions
What kind of image does 1D array produce?
2D imaging
What kind of image does 2D array produce?
3D imaging
Transmit steering
Sending pulses with a delay
What are 2 other terms for 3D imaging?
- Volume imaging
2. Volumetric scanning
What is 3D scanning mots common for?
Obstetrics
- breasts
What makes up 4D imaging?
3D imaging + time
