Intensity Flashcards
What is the equation for intensity?
Intensity (w/cm^2) = power/beam area
What is intensity?
Intensity is the concentration of the power in a beam. It’s a key parameter for bioeffects.
What is peak?
The maximum value
What is average?
The mean value
What is spatial?
Referring to distance or space
What is temporal?
Referring to all time (transmit and receive)
What is pulsed?
Referring only to the time the pulse exists (transmit only)
What intensity description has the highest value?
SPTP – spatial peak, temporal peak has the highest value.
Which intensity description is most important for thermal bioeffects?
SPTA-spatial peak, temporal average is most important with regard to bioeffects.
Does an ultrasound beam have the same intensity at different locations within the beam?
No
What is a logarithm?
Logarithm is a way of rating numbers by representing the number of tens that are multiplied together to create the number.
What is the log of 100? What is the log of 1000?
10x10=100 so the log of 100 = 2
10x10x10=1000 so log of 1000 = 3
Hint: count the zeros
What are decibels?
A logarithmic scale, a relative scale-a ratio of the final to the initial strengths.
A comparison, therefore, 2 intensities are needed to calculate decibels.
What are the units of relative amplitude?
Decibels
What does 3 dB mean?
2 times bigger
What does 10 dB mean?
The final intensity is 10 times bigger than the original intensity.
What is an intensity ratio of 50 dB?
100,000 times bigger than the original intensity
What does 6 dB mean?
Since 3 dB means two times bigger, 6 dB means 2×2. So the final intensity is four times bigger than the original intensity.
What does 9 dB mean?
Since 3 dB means two times bigger, 9 dB means 2×2×2. So the final intensity is eight times bigger than the original intensity
What does negative decibels mean?
The intensity is decreasing.
What does -3 dB mean?
It means the intensity has fallen to half the original value.
What does -10 dB mean?
It means we have fallen to 1/10th of the original value.