Lecture 17 Flashcards
Linear phased array is a ____ line of elements
Straight
In Linear phased array elements are fired with
A small time difference —> phasing
______us of time delay between each firing
<1us
Wave front created by the
Differing distances of the waves do to phasing
A wave always travels ______ to its wave front
Perpendicular
The new waveform created by secondary wavelets happens according to
Huygens principle
How do we stear a beam to the right
Phase the fire with the left side firing first
If all elerments are energized simultaneously then
There are no delays
The shorter the the delay between firing in elements than
The more horizontal the wavefront
How do we change the focus
Increase intensity —> improves intensity
Where is the beam width the smallest
At the focus
In electronic focusing the phased arry can also
Focus the beam
In electronic focusing greater durvature places the focus
Closer to the transducer
In electronic focusing less curvature moves focus
Deeper
In electronic focusing can move focus depth up or down based on the
Time delay
Greater time delay = _____ focus
Closer to the surface
How do we achieve curvature
Fire outside crystals first and fire the middle ones the last
an unfocused sound beam has
Natural focusing
Focus sound beam has
Electronic focussing
Multiple foci
They require multiple pulses, each focused at a different depth
Montage of overlaid images, better resolution at each depth
Decrease frame rate is lag
What is a further application for phasing
Spatial compounding
What is the purpose of spatial compounding
Hit the same object from different angles
Spatial compounding has more
Pulses per image
Allows to sharpen boarders, smoother image, clears out cysts
Phasing of a very small group of elements =
Sector image
Phased array can be used to assess
Large ares through very small windows
Phasing can be applied to each element group in a linear sequenced array to do the following :
Steer pulses in various directions
Initiate pulses at various starting points across the array
Vector aray is _____+ _____
Linear array + phased array
Vector array has a _____ top
Flat
Widescreen =
Sector
Vector array used to measure
Larger organs
In vector arrays, phasing applie to linear sequence array….
Keep delays the same for each group
Beams sent out in an angled direction
Parallelogram shaped display
Used in doppler ultrasound
Variable aperture
Not all elements of a phased array are used to generate all pulses
Smaller groups are used for short focal lengths
Larger groups for foci located at increasing depths
Two types of grating lobes
Sides lobes
Grating lobes
Side/grating lobes are ______ beams
Weaker
Grating lobes are from _________ interactions
Interelement
If side lobes/ grating lobes hit a strong reflector, they produce
Strong echoes
Examples of strong reflectors (diaphragm, gas, fetal bone)
Side lobe and grating lobes show as ____ that look like ______
Artifacts
Amniotic bands
How do we fix grating lobes? (3)
Apodization
Subdicing
THI
Apodization
Grating lobes come from the edges of the elements
We can reduce the amplitude of the voltage to the outside elements
The weaker beam going out results in weaker echo, allowing for less artifacts to be created
