Week 4 - Attenuation Flashcards
As a sound wave travels through tissue, it ___________.
Weakens
The deeper a sound wave propagates, it loses more and more _____________________.
Amplitude, power, intensity (Energy)
Attenuation depends on what 3 things?
Distance, frequency, and the media
Relation. Frequency and Attenuation.
Directly
Relation. Distance and Attenuation.
Directly
Attenuation is always measured in _______.
-dB (loss of energy)
What are the three sources of Attenuation?
- Reflection
- Scattering
- Absorption
What is the most important source of attenuation?
Absorption
T/F. Absorption is in the form of interference waves propagating outward and you can feel it happen internally.
False. Not even close. Absorption is in the form of HEAT. And you cannot feel it.
Which depth would show the greatest amount of attenuation? A. 10 mm B. 1.2 cm C. 0.05 m D. 4 cm
C. 0.05 m = 5cm
What is the attenuation coefficient range for soft tissue?
0.5 to 1 dB/cm for a 1MHz probe
State the equation for Attenuation.
Attenuation = Attenuation Coefficient x Distance x Frequency
What is enhancement caused by?
Lower C in fluids causing less attenuation
Penetration improves with _________.
a lower frequency probe
Resolution improves with ___________.
a high frequency probe
The greatest component of Attenuation is ________.
Absorption
The Attenuation coefficient in soft tissue = _________.
1/2 Frequency
More Energy is lost from _______ frequency sound than _______ frequency sound.
high, low
Half-Value layer thickness = _____________.
distance that reduces the intensity by 1/2
OR
the depth that results in 3dB of attenuation
The attenuation of Air is _____________.
Very High due to absorption and scattering
The attenuation of Bone is _________________.
Very High due to high absorption.
Which of the following transducers would be the best choice for scanning the greater saphenous vein? Why? a. 2 MHz b. 5 MHz c. 7 MHz d. 10 MHz
d. 10 MHz, the GSV is not a very deep structure, therefore a higher frequency would create the best image.
What is the term used to describe the brighter echoes deep to a liquid mass compared to adjacent tissues?
Enhancement
Why are the echoes deep to a fluid filled structure brighter?
The fluid has less attenuation than the adjacent tissues
Name the three components of attenuation.
Absorption, reflection, and scattering
As the path length increases, the attenuation of ultrasound in soft tissue ____________.
increases
Attenuation in lung tissue is ____________ the attenuation in soft tissue.
greater than
Attenuation in bone is __________ the attenuation in soft tissue.
greater than
Attenuation in air is _____________ the attenuation in soft tissue.
greater than
What are the units of attenuation?
dB (decibels)
T/F. In a given medium, attenuation is unrelated to the speed of sound.
True. Attenuation and propagation speed are unrelated.
What is the relationship between ultrasound frequency and the attenuation coefficient in soft tissue?
the attenuation coefficient in soft issue is approximately 1/2 the frequency.
What are the units of the half-value layer thickness?
distance (cm)
As frequency decreases, depth of penetration _________.
increases
As path length increases, the half boundary layer _________.
remains the same
As the path length increases, the attenuation coefficient of ultrasound in soft tissue ________.
remains the same
