Focus Flashcards
What is the purpose of focusing?
Improves lateral or axial resolution by concentrating the sound energy into a narrower beam.
What are the three methods of focusing?
External, with a lens
Internal, With the curved active element
Phased array, Electronics of the ultrasound system.
Define external focus:
Lens in front of PZT Crystal.
Define internal focus
Curved PZT, tightens and narrows the game. Most common form of fixed focus.
Define electronic focusing:
Achieved by phased array transducers. The ultrasound system electronics focuses the sound game. Sonographer can alter focus. Only with multielement transducers, never with single crystal transducers. More versatile than fixed focusing.
What alterations are made to the sound beam when focused?
Narrowing of the beam diameter in the near field and focal zone.
Focus/Focal point is moved closer to the transducer, NZL is reduced.
Diameter beyond the focal zone increases.
Size of the focal zone is reduced.
How are linear phase arrays and cardiac phased arrays focused and steered?
Groups of individual PZT crystals are fired sequentially and in a phase that steers and focuses the sound beam.
What is phasing?
Timing the firing of crystals to steer the beam and also to focus it at one or several points.
What part of the system Controls the phased firing of the PZT crystals
the pulses are controlled by the beam former that distributes the pulses in Delay patterns that sweep and shape the beam.
When the beam former creates a slope either left or right how does this affect the beam?
The beam is steered to left or the right. Slope = steering.
When being former creates the curvature how does this affect the beam?
A curvature will focus the beam as well as defocused the beam. Curvature = focusing
