Week 13- 2 Dimensional imaging Part 2 Flashcards
What does resolution refer to?
refers to the accuracy in imaging.
What is slice thickness?
elevational thickness
Image resolution deals with three dimensional space how?
- Shallow to deep
- side to side
- above to below the imaging plane.
What shape active element creates the best elevational resolution?
Disc-shaped crystals
What does Elevational resolution or Slice thickness refer to?
The height of the beam.
What axis does Elevation sit on?
z axis
Elevational resolution is best with what kind of crystal?
smaller crystals
What transducer has the best elevational resolution?
Annual phased array transducer
What are side lobes?
off-axis sound beams made by single-element transducers.
Where are side lobes found?
in the far field.
Do side lobes degrade or make lateral resolution better?
Degrades lateral resolution.
What are grating lobes?
Off axis sound beams that extend outside of the main beam.
What kind of transducers create grating lobes?
Array Transducers
What is apodization?
the altering of electrical spike voltages that reduce lobe strength. Reduces Side and grating lobes.
Side lobes
- sound is omnidirectional
- Some sound is directed off the main beam
- Structures within side lobes can generate reflections that create artifacts.
- Degrades Lateral resolution
Grading Lobes
- Sound is omnidirectional
- Sound is directed off the main beam.
- Structures with grating lobes can generate reflections that create artifacts.
- Degrades Lateral resolution
What are 3-D images made of?
Voxels
What 3 imaging planes does 3-D imaging use?
- Axial
- Lateral
- Elevational
What is Subdicing?
Active elements are cut into smaller pieces called sub elements.
What does subdicing reduce?
reduces grating lobes.
What is the aperature?
the “listening hole” or the number of elements used to create sound beams or to receive reflected echoes.
What does dynamic aperture change?
changes the shape of the sound beam.
Which of the following is an advantage of 1 1/2 D (dimensional) arrays?
reduced slice thickness
True or False, linear arrays create sound beams that are parallel and are evenly spaced at all depths.
True
True or False: A machine that displays a 2D image and Doppler is called a duplex scanner.
TRUE
Which of the following best describes the sound beam of an annular phased array transducer?
mechanically steered and electronically focused
The firing delay patterns of a linear phased array transducer:
focus the sound beam during transmission
What is a typical value for the electrical signal delays in a curvilinear phased array transducer?
10 ns
Which transducer creates a beam that is focused in all planes and at all depths?
annular phased array
Which transducer will improve elevational resolution?
1 1/2 dimensional array
What kind of transducer produces side lobes?
Single element transducers.
Mechanical
What kind of transducers create grating lobes?
Array transducers.
