Lesson 4 (Part 1) Flashcards
What does the reception channel of the beam former do?
Amplifies and combines the echo voltages from individual elements and sends them to signal processor
When we are with the signal processor what kind of signals are we dealing with?
Digital signals
What are the functions of the signal processor? (3)
- Filtering
- Detection
- Compression
What does pulsed wave US produce?
A bandwidth of transmitted frequencies
What is the strongest frequency?
Fundamental frequency
Bandwidth
Range of frequencies contained in a pulse
What kind of SPL do you have with a narrow bandwidth?
Long SPL
What kind of SPL do you have with a wide bandwidth?
Short SPL
Which length of bandwidth will give you a better axial resolution?
Wider
- shorter SPL
What does filtering do?
Gets rid of frequencies we do not want
How does filtering work? (3)
- Select the desired frequency for the bandwidth
- Pass a range of frequencies through it
- Rejects those above and below the bandwidth
What kind of filters does the signal processor use?
Bandpass filters
When might we adjust a filter?
When dealing with harmonics
Bandpass filter
A filter that passes a range of frequencies and rejects those above or below the acceptance bandwidth
What are tuned amplifiers used for?
To reduce noise
Why does the bandwidth decrease while the echoes return?
Because the higher frequencies in the bandwidth are more attenuated compared to the lower ones
What does an input filter include? (2)
- Echo signal bandwidth
2. Electronic noise with unlimited bandwidth
What is a filter bandwidth designed to accommodate?
A single bandwidth
Harmonics
Modification of the sinusoidal waveform as it propagates through the tissue
How do harmonics work?
Multiple frequencies are produced by fundamental frequency (fâ)
- odd and even multiples of fâ
What is the first harmonic sent out called?
The fundamental frequency
What does the 2nd harmonic being set out do?
Produces echoes that will allow for better resolution
What function do filters perform in signal processors?
Harmonics
What happens when we press the THI button?
The fundamental frequency is filtered out
What are the benefits for harmonics? (4)
- Narrower beam width
- Narrower in the z plane / thinner beam
- Side lobes/Grating lobes (artifacts) are eliminated
- Reduction of anterior reverberation
- harmonics beam is generated further into tissue
What kind of resolution do you get with a narrower beam width?
Better lateral resolution
What kind of resolution do you get with a narrower in the z plane / thinner beam width?
Better elevational resolution
How are side lobes/grating lobes eliminated with harmonics?
Because they are not strong enough to generate harmonics
