Lesson 17 (Part 1) Flashcards
Linear phased array
Straight line of elements
How are linear phased array elements fired?
Voltage applied with a small difference
Phasing
Firing with a small time difference
How much time is delayed between firing of each element?
< 1 us
When is the delay bigger?
When the beam has a larger angle
What happens when the delay is straight with the beam?
There is no delay
Wavefront
Angled line that is created by the different phasing arrays
How does a wave always travel?
Perpendicular to its wavefront
What does the new wavelength created by secondary wavelets happen according to?
Huygen’s principle
Huygen’s principle
Every point on a wave-front may be considered a source of secondary spherical wavelets which spread out in the forward direction at the speed of light
How do we steer the beam when scanning the patient?
By phasing
If you want to steer the beam to the right how is phasing organized?
On a left slope
If you want to steer the beam to the left how is phasing organized?
On a right slope
Why do we change our focus?
To get a better resolution
What can we change at a particular spot?
Intensity
When is beam width smallest?
At the focus
Electronic focusing
Using phased array to focus the beam
What happens in electronic focusing when you have a greater curvature?
It places the focus closer to the transducer
What happens in electronic focusing when you have a lesser curvature?
It places the focus deeper
- farther away from them transducer
How can electronic focusing move?
Based on time delayed
What does increase delay of beams lead to?
Greater curvature
- focus is closer to the surface
How do we achieve curvature? (2)
- Fire outside crystals first and so on
- 1 and 8, 2 and 7… - Fire the middle ones last
What does decrease in delay of beams lead to?
Lesser curvature
- farther focus
What does an unfocused sound beam have?
A natural focus
What is a focused sound beam the same as?
Electronic focusing
What does multiple foci require?
Multiple pulses
- each focused at a different depth
Montage
Overlaid images
What does montage lead to?
Better resolution at each depth
What happens when the frame rate decreases?
It lags
