Lesson 17 (Part 2) Flashcards
Spatial compounding
Hitting the same object from different angles
What is the benefit of spatial compounding? (3)
- Clears out cysts
- Sharpens borders
- Smoother images
What does spatial compounding have more of?
More pulses per image
Sector image
Phasing of a very small group of elements
What can sector imaging be used to assess?
Large areas through very small windows
Vector array
Phasing can be applied to each element group in a linear sequenced array
What do vector array’s do?
Steer pulses in various directions
How does vector array initiate pulses?
At various starting points across the array
What makes up a linear array? (2)
Linear array + phased array
What does a vector array have?
A flat top
What is vector array a combination of? (2)
- Sequencing
2. Phasing
What is another word for sector?
Widescreen
What is a sector used to measure?
Larger organs
What is vector array?
Phasing applied to a linear sequenced array
What is kept the same for each group in vector array?
Delays
How are beams sent out in vector array?
In an angled direction
What kind of display is vector array?
Parallelogram shaped display
When is vector array used?
In Doppler ultrasound
Are all elements if a phased array used to generate all pulses?
No
What are smaller groups of arrays used for?
Shorter focal lengths
What are larger groups of array used for?
For foci located at increasing depths
Side lobes
Usually represent unwanted radiation in undesired directions
Grating lobes
Are the maxima of the main beam, as predicted by the pattern multiplication theorem
What kind of interactions come from grating lobes?
Interelement interactions
What can happen in grating lobes?
It can hit a strong reflector and produce strong echoes
What are strong reflector examples the grated lobe can hit? (3)
- Diaphragm
- Gas
- Fetal bone
What do grating lobes show as?
Artifacts
What do grating lobes look like?
Amniotic bands
How do you fix grating lobes? (3)
- Apodization
- Subdicing
- THI
Apodization
Optical filtering technique
Where do grating lobes come from?
The edges of all the elements
What happens to the grating lobes if we reduce the amplitude of the voltage to the outside elements?
Less artifact
- weak beam is going out, so weaker echo is coming back
Can side lobes be apodized?
No
What does subdicing of each element into a small group of small crystals do?
Weakens grating lobes
What does subdicing reduce?
Inter-element interactions
What is subdicing only used for?
Grating lobe artifacts
When do you use THI?
When grating lobes or side lobes are too weak to produce harmonic signals
