Pulsed US and attenuation calculations Flashcards
What is the formula to calculate frequency?
propagation speed/wavelength
What is frequency indirectly proportional to?
Period (T)
What is the formula for pulse duration?
number of cycles in a pulse x period
(n x T)
What is the formula for SPL?
number of cycles x wavelength
How are PRP and PRF related?
They are inverses of each other
What is known as the amount of time where the US system is actually emitting sound?
Duty factor
How is duty factor calculated?
PD/PRP x 100
A 3dB decrease results in what percent reduction in amplitude?
50%
A 6dB decrease results in what percent reduction in amplitude?
75%
A 10dB decrease results in what percent reduction in amplitude?
90%
What is the formula for attenuation coefficient in soft tissue?
a(dB) = 1/2 x (frequency) x L
When calculating attenuation for a total round trip, what formula is used?
a(dB) = 2 x frequency x L
How to calculate acoustic impedence?
z = p (density) x c (propagation speed)
What is acoustic impedence?
Resistance to sound wave propagation
Will denser material have an increased or decreased impedence?
Increased
When z1 = z2, what will the result be?
Anechoic structure - there is 100% transmission
What artifact is due to refraction?
Lateral position artifact
When media 2 has a greater propagation speed than media 1, what happens to the angle of refraction compare to the angle of incidence?
When media 2 is greater, the refraction angle will be larger than the incidence angle
What unit is acoustic impedance measure in?
Rayls
What is known as the “frequency of sound waves due to a moving object”?
Doppler effect
What application is superior in detecting the presence or absence of flow?
Power doppler
What is a disadvantage of power doppler?
Cannot determine the direction
