Half-intensity depth, and Impedance Flashcards
What is half-intensity depth, (HID)?
The depth of tissue that results in 3 dB of attenuation to the intensity.
OR:
The distance sound travels in a tissue that reduces the intensity of sound to one-half its original value.
Name some half-intensity depth synonyms:
Penetration depth, depth of penetration, and
half-boundary layer
What are the units of half-intensity depth?
Always 3 dB of attenuation
How do you set up an attenuation problem?
Set up: Actual attenuation = coefficient x depth x frequency. Then: Solve for unknown.
Ex: dB = 0.5 x cm x MHz
As frequency decreases, depth of penetration ______.
Increases
As path length increases, the half boundary
layer _____ __ ____.
Remains the same
Impedance is associated with ___ __ _____.
Only the medium
As the path length increases, the attenuation coefficient of ultrasound in soft tissue:_______?
[increases, decreases, remains the same].
Remains the same
Acoustic impedance = _____ x _____.
Impedance (rayls) = density (kg/m3) x propagation speed (m/s)
Impedance is important in _____ at boundaries.
Reflections
What is impedance?
The acoustic resistance to sound travelling in a medium.
How do you calculate acoustic impedance?
Multiply the density of a medium by the speed at which sound travels in the medium.
What are the units of impedance?
Rayls. Impedance is often represented by the letter Z.
Impedance is determined by: _____?
Medium only.
It is calculated, not measured.
