Ch 7 Beam Former Flashcards
Differentiate principle 1 vs principle 2?
Principle 1:
-pulse echo technique
-phasing to focus
Principle 2:
-no more focus
-fewer pulses required
List the 4 pulse echo instruments in order?
-Beam former
-Signal processor
-Image processor
-Display
What is the beam former?
-Where the action originates
-Consists of 7 things (pulser, pulse delays, T/R switch, amplifiers, ADC, echo delays + summer)
List functions of the beam former?
-Generates voltages
-Determines PRF, coding, frequency + intensity
-Amplifying echo voltages
-Compensates for attenuation using TGCs
-Digitizing the echo voltage stream
-Directing, focusing + apodizing the u/s beam on transmission + reception
What does the pulser do?
-Generates the voltages that drive the probe
-Generates the production of a pulse
-Determines the PRF
Sequencing + phasing operations of array probes are carried out by what 2 things?
The pulser + pulse delays
What adjusts PRF?
The pulser - based on imaging depth
Why is PRF automatically reduced?
To provide proper display of returning echoes, which avoids range ambiguity artifacts
What are range ambiguity artifacts?
It places structures much closer to the surface than they should be
What is output power?
-Aka transducer driving, transmit power, drive voltage
-Displayed as a % or in dBs relative to max output
-The greater voltage amplitude produced by the pulser, the stronger the signal that gets transmitted through the pt
-Creates increased penetration + higher amplitude of returning signals
Is it assumed that for each pulse all echoes are received before the next pulse is sent out?
Yes! Although, echoes from deep structures created by a 1st pulse will arrive at the probe AFTER the 2nd pulse has been sent out
How is output power related to bioeffects?
Can lead to heating of tissue for sustained time
List 3 tasks that the pulser + pulse delays carry out?
-Sequencing
-Phasing
-Variations in pulse amplitudes (apodization)
What is a channel?
-An independent signal path consisting of a probe element, delay + possibly other electronic components
-There are 64, 128 or 192 channels
- # of channels never exceeds the # of elements in the probe
An increased # of channels allows for what?
More precise control of beam characteristics
(specifically sequencing + phasing of crystals)
Explain the transmit/receive switch?
During transmission:
-T/R switch opens path from the pulser to the probe elements
During reception:
-T/R switch opens path from elements to the reception amplifiers
(the switch protects the sensitive input components of the amplifiers from the large driving voltages from the pulser)
Define amplification?
To increase the amplitude of the returning signals
What are our amplifiers?
Our gain + TGC controls
(these make our returning echoes brighter)
The beam former has how many amplifiers for each channel?
1
What are radio frequency signals?
-Sound energy that is converted back into electrical energy
-Low level RF signal is the returning electrical signal
-The returning RF signals are weak + need to be amplified with gains
Explain time gain compensation (TGC’s)?
-Aka depth gain compensation
-Compensates for the effect of attenuation on an image (m/c about 60 dB of attenuation)
-Allows for compensation of signals that traveled a greater path length
Can later echoes be amplified to the same level of brightness as the earlier echoes?
Yes
What does lateral gain control do?
Adjusts gains laterally across image
(applied in cardiac scanning to help see ventricular walls)
What are analog-to-digital converters (ADC)?
They convert the analog voltages representing echoes to numbers for digital signal processing + storage
