12 Pulsed Echo Instrumentation Flashcards
Describe the ultrasound system.
The entire device that produces sound beams, retrieves the echoes and produces visual images and audio signals
What is the information processed by the ultrasound system?
Time of flight
Strength of reflection
Direction
Frequency (for Doppler)
List the six interconnected components of an ultrasound system.
Master synchronizer Transducer Pulser Receiver Display Storage
What does the master synchronizer do?
Communicates with all of the individual components of the ultrasound system
Organizes and times their functions, so as to operate as a single integrated system
What does a transducer do for an ultrasound system?
Converts electrical into acoustic energy during transmission
Converts returning acoustic into electrical energy during reception
What does a pulser do?
Controls the electrical signals sent to the active elements for sound pulse generation
Determines the pulse repetition period, PRF, and pulse amplitude
Creates the firing pattern for phased array systems, beam former
What does a receiver do for an ultrasound system?
The electronics associated with processing the electronic signal produced by the transducer during reception and producing a picture on a display device
What is the display device for an ultrasound system?
The device associated with the presentation of processed data for interpretation
What is the storage for an ultrasound system?
Any number of devices and media that are used to permanently archive the US data
What do the pulser signals depend upon?
System and transducer
What are the different pulser modes?
Continuous wave
Pulsed wave, single crystal
Pulses wave, arrays
What type of wave occurs with continuous wave pulser modes?
Constant electrical signal in the form of a sine wave
What does a pulsed wave, single crystal pulser mode create?
Short duration electrical spike, 1 electrical spike per US pulse
What does a pulsed wave, arrays pulser mode create?
Many elements fired for each ultrasound pulse
What is transducer output?
Output gain, acoustic power, pulser power, energy output, transmitter output
What is the effect upon the image if the transducer output is changed?
Affects brightness of the entire image
The strength of every pulse transmitted to the body changes
What is the signal-to-noise ratio?
Meaningful portion of the data versus inaccurate portion of the data
What is the signal-to-noise ratio when a high-quality image I s created?
High signal to noise ratio
What is the signal-to-noise ratio when an image is degraded?
Low signal-to-noise ratio
What is the overall function of the receiver?
Boosts the strength of the signals returning from the transducer, processes them and prepares them for display
What is the order of the functions of a receiver?
Amplification, compensation, compression, demodulation, rejection
What is the purpose of amplification?
Increases the strength of all electrical signals in the receiver prior to further processing
Can the amplification be adjusted by the sonographer?
Yes
What is the effect of amplification upon an image?
Every signal is treated identically, thus, amplification changes the brightness of the entire image
What does a preamplifier do to the signal?
Alters the signal before it is amplified, often performed in the probe
What is the purpose of compensation?
Used to create image of uniform brightness from top to bottom
What is the effect of compensation upon the image?
Makes all echoes from similar reflectors appear identical regardless of their depth
Can compensation be adjusted by the sonographer?
Yes
How is TGC and frequency related?
More TGC is used with higher frequency because of more attenuation
What will you adjust if you cannot see reflectors in the near field or far field on your image?
TGC
What is the purpose of compression on an image?
Keeps signals within the operating range of the system’s electronics and the grayscale within the range of what the human eye can see
Decreases the dynamic range of the signals
What is the effect of compression upon an image?
Changes the grayscale mapping
Can compression be adjusted by the sonographer?
Yes
How are decibels affected by compression?
They add or subtract
What is the purpose of demodulation?
Changes the signal’s form to one more suitable for display
Can demodulation be adjusted by the sonographer?
No, it is done automatically
What are the 2 steps of demodulation?
Rectification – corrects for or eliminate negative voltages
Smoothing – putting an envelope around the bumps to even them out
What is the purpose of rejection?
Displays low-level echoes only when they are clinically meaningful
Low-level noise is eliminated in images
What is the effect of rejection upon an image?
Affects only low-level signals everywhere on the image, but does not affect bright echoes
Can rejection be adjusted by the sonographer?
Yes
What are contrast agents?
Micro-bubbles of gas entrapped in a shell
What allows contrast agents to be seen?
Different acoustic fingerprint
Large impedance difference between contrast agents and biologic tissues and creates strong reflections
What are requirements for contrast agents?
Safe Strong reflector of US Long persistence Small enough to pass through capillaries Metabolically inert
What adjustments alter brightness of the entire image?
Output power or Receiver gain
What is output power?
Affects brightness by adjusting the strength of the sound waves sent to the body from the transducer and affects patient exposure
What is degraded when the image is too bright from high output power?
Lateral and longitudinal resolution
What is receiver gain?
Affects brightness by changing the amplification of the electronic signals after returning to the receiver
What is ALARA?
As Low As Reasonably Achievable
Minimize patient exposure
