Intensities Flashcards
If you double the amplitude, what happens to intensity? Amplitude x3 means… ?
It is increased x4 (due to the exponent).
Intensity x9
What is power?
What are the units for power?
Energy per unit time.
Watts
What is sound intensity?
What are the units for intensity?
What are the (usual) ultrasound units for intensity?
Power per unit area.
W/m2
mW/cm2
What is the equation for intensity?
Intensity = power/area,
OR: Intensity = amplitude2 /2pV
True or false:
Amplitude and frequency are dependent on each other.
False, they are independent of each other.
What are the two basic parameters in measurements of intensity?
Space and Time
What are the two types of measurements of intensity?
Peak and Average
Which measurement will be higher?
Peak or Average?
Peak
What does peak refer to?
The maximum value
What does average refer to?
The mathematical middle value
What does temporal refer to?
To all time, Transmit (pulse duration) and Receive. .
True or false:
A pulsed ultrasound beam does not have the same intensity at different times.
True
What does pulsed refer to?
Only to the transmit time (pulse duration).
True or false:
A pulsed ultrasound beam has the same intensity at different times during the pulse.
False: It has does not have the same intensity at different times during the pulse.
Pulsed is the average intensity for what?
For the pulse duration only. (Ignore listening time).
If TP = TA, what kind of ultrasound is it?
Continuous wave: always on.
So, peak intensity = average intensity.
What is Im?
Another type of intensity measurement.
It’s the average intensity measured at the most intense half-cycle.
What is pulse average, PA?
And what type of measurement is it?
The average intensity for the duration of the pulse itself.
It is a measurement of time.
What does spatial refer to?
Location or space. (Distance)
What is spatial peak intensity, (Isp)?
The average intensity at the location where it is maximum. (the maximum in space)
What is spatial average intensity, (Isa)?
The average intensity across the beams cross sectional area.
True or false:
Spatial average intensity, or Isa, is always higher than spatial peak intensity, or Isp.
False. Spatial peak intensity is always higher.
What is this all about?
Why do we care?
Sound energy.
We don’t want our sound waves to damage tissue.
What is beam uniformity coefficient (BUC)?
Another intensity related measurement.
Sometimes called: SP/SA)
Why is a BUC closer to 1.00 optimal?
It suggests a uniform intensity across the area.