Week 14 pulsed Echo Instrumentation part 1 Flashcards
Chapter 14
What does a Pulser do?
Creates the electrical singal that excites the PZT.
What does a pulser determine?
The amount of power going into a patient.
When does the Pulser function?
During transmission
What happens when the pulser is set to a low voltage?
The reflected echoes are weak and the entire image tends to be dark.
What happens when the pulser is set to a high voltage?
The reflected echoes are stronger and the entire image is brighter.
What does the pulser impact?
output power
What does the Pulser control?
- Amplitude
- PRP
3.PRF
What is the beam former?
Creates and determines the delay pattern for array transducers.
steering (sloped)
Focus ( curved)
What is the Thermal Index?
The thermal index determines how much heating there is in the tissue.
What is Mechanical Index?
Measures changes to the energy around the cells that are being imaged. (Cavitation)
Are Ti and Mi adjustable?
Yes
What is the acceptable voltage range that is able to be sent into the body?
0-100 volts
What does ALARA stand for
As
Low
As
Reasonably
Possible
What does increased output power create?
increased Ti and Mi
What does the beam Former control?
Apodization
What does a signal refer to?
Meaningful reflections returned to the transducer.
What happens to the output power if the signal to noise ratio is increased?
output power increases, making noise less significant.
What is the signal-to-noise ratio?
a comparison of the meaningful information (signal) in an image, compared to the amount of contamination (noise).
When the signal-to-noise ratio is high, what happens to the image quality?
the signal is stronger than the noise and the image quality is higher.
What happens to image when the signal to noise ratio is low?
The strength of the signal is closer to the signal of the noise, degrading image quality.
How does transducer output affect noise?
As output power increases, the signal-to-noise ratio also increases.
What is apodization?
When the beam former adjusts electrical spike voltages to reduce lobe artifacts.
What are the functions of the pulser?
determines PRP, PRF and amplitude of the outgoing signal
The beam former determines the
firing delay patterns of phased array systems
What is needed to create a display on the US system?
scan converter
When a pulser is set to a low voltage
the active element vibrates gently
The big advantage to lower pulser voltages
minimize patient exposure
A great advantage of high output power:
improved signal to noise ratio
How does transducer output power affect noise?
power increases-signal dominates the image, noise disappears
What is the most common way to improve signal to noise ratio?
Increase output power
What US machine control determines the time between one voltage spike and the next?
Pulser
Why are lower pulser voltages desirable?
decrease transmitted acoustic energy
minimize patient’s exposure to ultrasound energy
minimize likelihood of bioeffects
What sets the rate of the pulser & pulse delays?
PRF
