Module 3 Review Flashcards
Discuss why the concept of beam width is so important to sonographers?
The beam width determines lateral resolution
State the ways in which the ultrasound beam changes with changing distance from the crystal
- Non uniform intensities in the converging near field.
- Diverges at the focal point to become more uniform in the far field
Using a non-focused probe, at which point is the ultrasound beam the narrowest and how wide is it at this point?
Most narrow at the focal point equal to one half the crystal diameter
How wide is the beam at 2 near zone lengths (assume unfocused probe)
Equal to the crystal diameter
What determines the width of the beam? 3
- The aperture
- Frequency
- Distance from transducer face
Where does the far zone end?
Where there is total attenuation of the sound
State synonyms for near and far zone?
Near = fresnel
Far = Fraunhofer
Which formula is used to determine the length of the near zone?
NFL = (D^2)/lamda or ((D^2)(6))/6
What causes side lobes?
Radial mode vibrations
How are side lobes controlled?
The insulator ring
Why are side lobes bad?
Give artifactual information on the display
Distinguish the elevational axis from other beam dimensions?
It is the z plane
Hey is the concept of effect beam width so important for sonographers?
Understanding what this is allows for the best images possible
State the formula for calculating the angle of beam divergence in the far field
Sin = (1.2*lamda)/ diameter (where diameter of crystal is D)
State the ranges of weak, medium, and strong focus
- Weak: 7-19 cm
- Medium: 4-10 cm
- Strong: 1-4 cm
