Exam 3 - Lesson 6 Flashcards
Focusing
active focusing reduce beam width to improve image
Acoustic Lens
curved lens placed in front of flat crystal to focus beam
Acoustic Mirror
placed behind crystal to focus
Curved Crystal
Flexible ceramic, piezoelectric material that bends to make its own focus by increasing intensity in focal zone
Electronic (Dynamic) Focusing
AKA Phasing - Array transducer electronically activated in time delays
What does electronic focus look like?
Arched
What is the most widely used focusing?
weak : long , narrow focal zone (longer - greater depth)
What does focusing improve?
Image resolution
Beam steering
Mechanical: produced with motor (focused & steered)
Steering on a slope / Focusing on a curve
What does phasing mean?
Time delays in excitations
What does phasing focus/ steering do?
delays return signal to allow echos to all return at the same time. Greatest delay applied to closest signal
Sequencing in linear probe
Electronically excited but NO PHASING (focus/ steer)
- Large array’s in burst sent out in linear form without a time delay
In a 2D image w/ color box what is the color box? what is the 2D portion?
Color box = steered (phased)
2D black & white = sequencing
Which focusing method produces a fixed focus? Meaning it can not be adjusted..
Lens, mirror, crystal, beam steering
What does not have a fixed focus?
electronic (dynamic) focusing - phasing : we change the time delay
