Ch. 14 Physics: Pulse Echo Instrumentation Flashcards
What are the 2 major functions of the US machine?
creation of the sound beam
processing the received signals into diagnostic information.
What are the 6 components of the US system?
Transducer
Pulser and beam former
Receiver
Display
Storage
Master synchronizer
What does the transducer do during transmission?
transforms electrical energy into acoustic energy.
What does the transducer do during reception?
converts returning acoustic energy into electrical energy.
Creates electrical voltages that excite the transducer’s PZT to produce sound beams
Pulser
When does the pulser function?
During transmission
What determines the amplitude, PRP, PRF?
Pulser
What are the ranges for the Transducer Output?
0 to 100 volts
What controls the overall brightness of the reflected echoes?
Output
If the pulser is set low, will the image be dark or bright?
Dark
If the pulser is set high, will the image be dark or bright?
bright
What are the synonyms for pulse voltage?
Output gain, acoustic power, transmitter output, power, or gain
True or false:
Output gain/Transducer output is controlled by the sonographer
True
Transducer Output is standardized by what two mathematical calculations?
Thermal index (TI)
Mechanical Index (MI)
True or false:
Thermal index (TI) and Mechanical Index (MI) help determine bioeffects.
True
_________ voltages increase the likelihood of thermal heating or bioeffects to occur.
Higher
_______ voltages are most desired, when overall image quality is still optimal.
Lower
Decreased energy =
less bioeffects
a disturbance that degrades image quality by interfering with the clarity of a signal.
Noise
A comparison of the meaningful information in an image, compared to the amount of contamination present.
Signal-to-noise ratio
Meaningful information =
signal
Contamination =
noise
High ratio =
high quality/high signal
Low ratio =
low quality/low signal, high noise presence resulting in a less diagnostic image
Increasing power output will ________ the signal-to-noise ratio
increase
In addition to the transmission output, the pulser also determines the __________ of the voltage being given
timing
Longer delays means
longer pulses (long PRP)
Shorter delays means
shorter pulses (short PRP)
PRP is affected by what?
depth
A short PRP means ______ PRF
high
A long PRP means _______ PRF
low
creates and distributes the delay pattern for array transducers.
Beam former
What happens to the beam former during transmission?
Coordinates the signals sent to each active element to optimize the transmitted beams
Adjusts the electrical spike voltages to reduce lobe artifacts (apodization)
What happens to the beam former during reception?
Establishes the time delays used for dynamic receive focusing
Controls dynamic aperture by varying the # of crystals used during transmission and reception
What Protects sensitive components from the high voltage transmit signals in the beam former?
the switch
What Directs electrical signals from the transducer to the appropriate electronic and processing components in the beam former?
The switch
What is made up of A single PZT element in the transducer, The electronics in the beam former/pulser, and The wire that connects them all?
The channel
The number of elements that can be excited simultaneously is determined by
The number of channels
How many channels do most systems have?
32-256
What prepares the information in the received signals for display on the system’s monitor?
The receiver
The 5 receiver operations must be performed in this order:
(conveniently in alphabetical order)
Amplification
Compensation
Compression
Demodulation
Reject
contains the pieces that create, carry, and transmit the voltage into a signal
the channel
processes the electric signals returned from the transducer and prepares the information for display.
The receiver
the first process performed by the receiver upon reception of reflected signals
Amplification
All returning signals undergo …..
amplification
True or false:
Amplification cannot distinguish between signal and noise; it increases both identically.
True
True or false:
The entire image is made brighter or darker when the sonographer adjusts the receiver gain
True
the second function performed by the receiver
Compensation
True or false :
The sonographer can adjust compensation with a series of slider bars
True
What are the synonyms for compensation?
Time Gain Compensation (TGC)
Depth Gain Compensation (DGC)
Swept Gain
Sound waves weaken the deeper they travel producing progressively dark images. _______________ counteracts this natural occurrence, by creating uniform brightness at ALL depths.
Compensation
What controls allow the Sonographer to make the appropriate adjustments to compensate for the loss of gain as the image depth increases, and signal strength decreases?
TGC -Time Gain Compensation
the third function of the receiver
compression
What decreases the dynamic range of a signal?
compression
Compression is also known as …..
log compression or dynamic range
Compression is reported in what?
dB
True or false:
Compression increases the contrast resolution of only part of the image
False
entire image
the fourth function of the receiver
Demodulation
What are the two-part process that changes the electrical signals within the receiver into a form suitable for display on a monitor?
Rectification
Smoothing
Can the sonographer adjust demodulation?
no, it is not adjustable
What is the purpose of demodulation?
to change the form of the electrical signal, but has no visible effect on the image
AKA Threshold or Suppression
reject
allows the sonographer to control whether low-level gray scale information will appear on the image, reducing electronic noise
reject or threshold
By increasing the threshold, you _______ the appearance of weak echo signals
decrease
What are the two levels of reject in the ultrasound system?
One that is built into the system
And the other is user adjustable
What are the 5 functions of the reciever?
Amplification of both pulses
Compensation for weaker pulses
The difference between the pulse amplitudes are reduced
The pulses are converted to another form
The weaker pulses are removed
Are Output Power and Receiver Gain adjustable by the sonographer?
yes
When is output power adjusted?
during transmission
when is receiver gain adjusted?
during reception
What Affects image brightness by altering the strength of the sound being transmitted into the body and Improves signal-to-noise ratio?
output power
What Alters the strength of the voltage received in the transducer during reception and Signal-to-noise ratio remains unchanged ?
Receiver gain
Which exposes the patient to bioeffects? output power or receiver gain?
output power
What is ALARA?
As
Low
As
Reasonably
Achievable
when should the principle known as ALARA be used?
when making power output changes
To correct an extremely bright image, what adjustment would you make first?
Decrease Receiver Gain?
Decrease Output Power?
Decrease Output Power
To correct an extremely dark image, what adjustment would you make first?
Increase Receiver Gain?
Increase Output Power?
Increase Receiver Gain
