Flashcards in The System Deck (42):
What does the computer processor in the system keep track of?
time of flight
strength of the echo
direction the echo is coming from
a system produces ________ _________ from the echo ________ received from the transducer
What is the definition of a system?
entire device that produces the beams
retrieves the echoes
produces the visual images and audio signals
What are the parts of the system?
pulser and beam former
all electronics and software
Each crystal has a ______ called a ______
What is transducer output?
determined by the excitation voltage of the pulser
piezoelectric element vibrates with a magnitude of pulser voltage
increasing the output by 3dB does what to the intensity?
What are the synonyms of the transducer output?
different manufacturers use different titles for the same idea
How do you adjust the transducer output?
by changing the power
If you make the power higher what happens to the picture?
you get a brighter picture
improves the signal to noise ratio (less fuzziness)
changes every pulse into the body
What is the Master Synchronizer?
communicates with all components
organizes and times functions
prepares components to operate as a single integrated system
What instructs the pulser to send an electrical signal to the transducer?
brain or manager of the system
Where is the pulser?
IN the beam former (aka: transmitter)
What does the pulser do?
pulse delays - phasing - focus and steer
transmit receive switch
summer - adder of signal compnents
What does the beam former do?
creates electrical spikes (pulses)
rocks the PZT
When does the beam former function?
electronics in the US machine that creates the electrical spikes/pulses that go through the wire and rock the PZT
functions during transmission
receives the timing signal from the master ad produces and electrical voltage (10-500 volts)
communicates with the receiver at the moment the element is excited
Who drives the transducer?
the Beam Former
If you have a low voltage PZT what happens to the output signal
does not vibrate as much - weak output signal
high voltage = PZT vibrates more - strong output signal
What does the beam former determine?
firing and time delays
How does the beam former work in a CW transducer?
constant electrical signal
electrical frequency = ultrasound frequency
how does the beam former work in CW, PW single crystal, and PW phased arrays?
CW: constant electrical signal (electrical frequency = US frequency)
PW Single: one electrical spike per pulse
PW Phased: one electrical spike per fired element therefore many spikes (patterns changes)....beam former creates delays
who is in charge of apodization?
the beam former
adjusts the voltages to reduce grating lobe artifacts
if you have shallow scanning pulses what happens to PRP and PRF?
What is coded excitation?
driving voltage forms (happens in the beam former)
What does the Processor do?
continues to process the signals
Master synchronizer > Beam former > Processor
Who does the processor send the signal to?
the receiver (found IN the processor)
What does the receiver do?
takes the weak signals from the transducer and converts them and boosts the strength of the signal
receives and processes the echo info
master > beam former > processor >receiver
What are the five functions of the receiver?
must be in order
in the receiver what does amplification do?
increasing the strength of all electrical signals in the receiver
increases or decreases the strength of all returning echoes*
what is a dB?
ratio of output electrical strength to input electrical strength of the amplifier
What does NOT change the signal to noise ratio(power)?
In the receiver there is compensation. What does it do?
makes all echoes from similar reflectors appear identical regardless of depth
TGC - DGC - Swept gain (sonographer adjusted)
Why is compensation needed?
due to the effects of attenuation
Higher frequency = ________ attenuation? what do you do with TGC?
greater .... more TGC
lower frequency = < attenuation needs less TGC
In the receiver you have compression. What does it do?
decrease the difference between large and small amplitudes
(adjusted with the dynamic range/compression button) aka: gray scale mapping
in the receiver there is a demodulator. What does it do?
demodulation or detection changes the signal's form
cannot be changed by the sonographer
rectification (turns negative voltages into positive)
smoothing or enveloping (put an envelope around the bumps to even them out)
prepares the signal for display
in the receiver there is a rejection function. What does it do?
displays low level echoes only when clinically meaningful
aka: suppression, threshold
affects all low level signal and throws them out
can be controlled by the sonographer (reject, threshold, suppression button)
What are harmonics?
creating an image from sound reflected at twice the fundamental frequency
done in the processor
non linear behavior
What happens to the frequency when you put harmonics on?
it multiples the fundamental frequency
What components do you adjust to yield a good representation image?
adjust the overall gain (amplification)
and then TGC (compensation)
What does compensation do?
provides equal amplitude for all similar structures regardless of depth
compensation - dB