Chap 3 Level 2 Flashcards
What is echogenicity
Refers to the strength or type of signal reflection
What is anechoic
- No echogenecity (no reflected signal)
- fluids, blood, bile, serous
What is hypoechoic
- low echogenecity (low level reflected signals)
- fatty plaque, some masses
What is hyperechoic
-high echogenecity (moderate to high reflected signals)
What does Calcified mean in echo
- strongly echogenic
- usually has acoustic shadowing
- normally moving parts
What is complex echoic
- mixed echogenecity (some bright, some dark)
What are the 2 terms
That describe how uniform the signal appears
- homogenous implies signal is uniform
- heterogenous implies there’s variation in the image w/in the signal
Plaque surface characteristics for smooth
- a continuous smooth surface that tends to be less symptomatic
Plaque surface characteristics for irregular
Discontinuous surface structure that tends to be more symptomatic and like to embolize
Soft tissue attenuation rate w/ formula
(0.5 dB/cm-MHZ)*(cm)(mhz)
When frequency and depth increase, what else increases
Attenuation
When does scattering occur
Scattering occurs when tissue is rough in respect to the wavelength
What happens when waves go from a constructive interference to a destructive interference
Creates a finer speckle pattern
What are two types of speckle patterns and their characteristics
- coarse speckle patterns: rough looking texture (larger black spaces)
- fine speckle pattern: smooth looking texture (smaller black spaces)
%reflected and %transmitted equation
%reflected = (z2-z1/z2+z1)^2
%transmitted = 1 - (Z2-Z1/Z2+Z1)^2
What does attenuation represent?
Transfer of energy through absorption and scattering
What is absorption in the context of attenuation?
Conversion of wave energy into heat
What is the dominant form of attenuation in soft tissue?
Absorption
How does attenuation through absorption change with frequency?
Increases exponentially with higher operating frequencies
What factors determine the amount of energy reflected?
Acoustic impedance mismatch, incident angle, type of reflection
What are the three categorizations of reflection?
- Specular reflection
- Scattering
- Rayleigh scattering
What determines specular reflection?
Smoothness and size of the reflector relative to the wavelength
Is specular reflection angle dependent?
Yes, it is highly angle dependent
What causes scattering?
Occurs from surfaces that are rough relative to the wavelength
What is Rayleigh scattering?
Occurs when reflectors are small relative to the wavelength (RBC)
What is the formula for acoustic impedance?
Z = Density x propagation velocity
