Chapter 14 Pulsed Echo Instrumentation Flashcards
What are the 2 major functions of ultrasound systems?
preparation and transmission (electrical signals to the transducer which creates a sound beam)
reception (receives electrical signals from the transducer; which processes images into clinically meaningful images and sounds)
The ___________ of electrical signals to the transducer, which creates a sound beam.
preparation and transmission
The __________ of electrical signals from the transducer, with subsequent processing into clinically meaningful images and sound.
reception
What are the six major components of ultrasound systems?
- Transducer
- Pulser and beam former
- Receiver
- Display
- Storage
- Master Synchronizer
Transforms electrical energy into acoustic energy. During reception, it converts the returning acoustic energy into electrical energy. This describes?
Transducer
The component of the ultrasound system that creates and controls the electrical signals sent to the transducer that generate sound pulses.
Pulser and Beam Former
The _______ determines the amplitude, pulse repetition period, and the pulse repetition frequency.
pulser
The _______ determines the firing delay patterns for phased array systems.
beam former
The component that transforms the electrical signals from the transducer (produced by the reflected sound) into a form suitable for display.
Receiver
What component of the ultrasound system presents the processed data?
Display
What component of the ultrasound system archives the ultrasound studies?
Storage
The component of the ultrasound system that maintains and organizes the proper timing and interaction of the system’s components.
Master Synchronizer
When does the pulser function?
during transmission
When the pulser is set to a low voltage the image tends to be ________.
darker
When the pulser voltage is high, the image tends to be _______.
brighter
What are the synonyms for pulser voltage (transducer output)?
output gain acoustic power pulser power energy output transmitter output power gain (don't use this one cause its to vague)
Can the sonographer adjust transducer output?
yes
Changes in transducer output affect the brightness of ___________.
entire image
defined as a random and persistent disturbance that obscures or reduces the clarity of a signal. contaminates images with low level undesirable signals
noise
What is signal to noise ratio?
comparison of the meaningful info (signal) in an image, compared to the amount of contamination (noise)
When the signal to noise ratio is ______, the signal is much stronger than the noise and the image is of high quality.
high
A ______ signal to noise ratio results in poor image quality.
low
Increasing output power is the most common way to __________ the signal to noise ratio.
improve (increase)
PRP and PRF are ________.
reciprocals
- Shorter listening time
- shorter pulse rep. period (PRP)
- higher PRF
All of these will result in shallow or deep imaging?
Shallow imaging
- longer listening time
- longer pulse rep. period (PRP)
- lower PRF
All of these result in shallow or deep imaging?
Deep Imaging
The beam former adjusts electrical spike voltages to reduce lobe artifacts in a process called ___________.
apodization
Modern beam formers use advanced microproessor technology and produce signals in digital format. This state of the art device is called?
digital beam former
made up of a single active element, the electronics in beam former/pulser and the wire that connects them.
channel
most systems have between ___ to ___ channels
32 to 256
Order of receiver operations
- Amplification
- Compensation
- Compression
- Demodulation
- Reject
What is amplification?
(aka: receiver gain) 1st function of receiving- each signal returning from the transducer is made larger; each signal undergoes equal amount of amplification
Is amplification adjustable by sonographer? And what is the effect on image?
yes; the entire image is made brighter or darker.
What are the units and typical values for amplification?
decibels; 60 to 100 dB
The process of improving the quality of a signal before it is amplified. occurs as close to the pzt as possible, often within the transducer
preamplification
What is compensation?
TGC settings (aka: time-gain compensation, depth gain compensation DGC, and swept gain) 2nd function of receiving- prevents the image from becoming progressively darker with increasing depth
With the TGC curve, what does the x-axis and y-axis represent?
x-axis: the amount of compensation
y-axis: reflector depth (starting at skin level)
At superficial depths, reflections undergo a small, constant amount of compensation called the?
near gain
The depth at which variable compensation begins is known as the?
delay
In the region of the _______, compensation corrects for the effects of increasing attenuation that result from increasing path length.
slope
At the depth of the _______, reflections are maximally compensated by the ultrasound system.
knee
The _______ indicates the maximum amount of compensation that the receiver can provide.
far gain
What is compression?
3rd function( aka: log compression, dynamic range)- keeps image grayscale content within the range of detection of the human eye
Why is log compresion important
clinically important because most meaningful backscattered signals from biologic tissues are very weak and the sonographer must be able to see differences in these weak reflections
Is compression adjustable by sonographer?
yes
What is demodulation?
4th function- 2 part process that changes the electircal signals within the receiver into a form more suitable for display on monitor
One of the two-part process of demodulation:
converts all negative voltages into positive voltages. It corrects for, or eliminates, negative voltages.
Rectification
One of the two-part process of demodulation:
places a smooth line around the “bumps” and evens them out.
smoothing (or enveloping)
Is demodulation adjustable by the sonographer?
no
What is reject?
5th function (aka: threshold, suppression)- allows sonographer to control whether low level grayscale info within the data will appear on the displayed image Most systems have 2 levels of reject; one that is built into the design of the system(cannot be changed), the other is user adjustable Affects low level echos only, not high level echos
what is the difference between output power and receiver gain? why is it important to appreciate this difference?
output power affects image by adjusting the sounds strength on transmission
receiver gain (amplification) alters the sound strength during reception
pt exposure to sound energy is affected by alterations in output power, but not by amplification
What is ALARA?
As Low As Reasonably Achievable
