Lecture 4 Flashcards
The reception channel of the beam former amplifies and combines the echo voltages from individual elements and sends them to
Signal processor
At the signla processor we are dealing with _____ signals
Digital
3 parts to the signal processor
Filtering
Detection
Compression
Pulsed wave US produces a ________ of transmitted freq
Bandwidth
_____ frequency is the strongest
Fundamental
We have a ______ of returning echo frequencies
Bandwidth
What is filtering
Getting rid of the frequencies in the bandwidth that are not important
When bandwidth is wide = SPL is
Slim
Is a wide bandwidth good
Yes
Filter passes _____
Range of frquency
The filter reject ____ and ____ the filter bandwidth
Above and below
What is harmonics
Modification of the sinusoidal waveform as it propagates through the tissue
Multiple frequencies are produced as harmonics by
Fundamental frequency
What do harmonic frequency produce
Echoes that will allow for better resolution
What performs harmonic function
Filters in sign processor
Echos from _____ and ______ are recieved at filter
Fundamental freq and second harmonic echo bandwidth
At the signal processor, the __________ is filtered out
Fundamental frequency
When is the filtering of the fundamental frequency occur
When we press THI
Benefit of harmonics in a narrower beam
Better lateral resolution
Benefit of narrower in the z plane
Better elevation resolution
Why do harmonics eliminated side/grating lobes
Because they are not strong enough to generate harmonics
Harmonics also benefit by the reduction of _______
Reverberation
Anterior reverberation is aka
Main bang
Reflections between the transducer face and skin surface cause
Multiple horizontal lines of echoes to appear in the near field
Where is a common spot fot anterior reverb to occur
Happens at the ribs
Why do harmonics lead to a smaller chance for anterior reverb
The main bang ehcoes are filtered
Overall benefits of harmonics
Better detailed resolution
Reduced artifacts
Less grating lobe artifacts
Less anterior reverberation
Draw back 1 of harmonics
Decrease penetration
Drawback of 2 of harmonics
Worse axial resolution
Why does harmonic give worse axial resolution
The transducer must fit the bandwidths of both F0 and 2F0
Therefore the bandwidth on each will be small compared to the overall bandwidth of the transducer
