Lecture 6 Flashcards
What happens to sound at the boundaries when sound is transmitted?
It passes through and continues on
Definition of Reflection
Sound bounces back to the transducer
Definition of Scatter
Sound is sent in different directions
Definition of Refraction
Sound beam is bent and sent in a different direction
Scattering occurs more frequently in tissue that is (homogenous/heterogenous)
Heterogenous
Definition of Specular Reflection
Reflection off a large, smooth boundary
How does the sound beam occur in specular reflection?
Perpendicular
Synonyms for Specular Reflection
Normal, orthogonal, 90 degree incidence, right angle incidence
A sound beam will be _____ or _____ when coming in at a 90 degree angle
Reflected or transmitted
Backscatter
Sound returns to transducer from a non-specular reflector
Definition of Non-Specular Reflection
Reflection from large, rough surfaces
(T/F) Scattering occurs when the reflector is smaller than the SPL
False, scattering occurs when the reflector is smaller than the wavelength
Which is stronger? Reflection from a non-specular reflector or specular reflector?
Specular reflection is stronger b/c the boundary is smooth, reducing scatter
Definition of Rayleigh Scattering
Sound is redirected in all directions due to the small size of the reflector ( < wavelength). Weakest return to probe
What reflectors in the human body produce Rayleigh scattering?
Red blood cells
Which modality is most affected by Rayleigh scattering?
Doppler
In Doppler, sound beams are reflected off of red blood cells whereas in ultrasound, the beams are reflected off tissue.
(T/F) Rayleigh scatter is not affected by frequency
False, directly related to Rayleigh scattering.
Frequency ↑, scattering ↑
Definition of Incident Sound
Sound that is coming from the sound source & going into the medium (BEFORE boundary)
Definition of Transmitted Sound
Sound that continues to propagate in the direction it was going AFTER hitting a boundary
Definition of Reflected Sound
Sound that is RETURNED to transducer after hitting boundary
Equation for Incident Sound
Incident sound = transmitted sound + reflected sound
Definition of Incident Intensity
Intensity of a sound BEFORE hitting a boundary/interface
Definition of Reflected Intensity
Intensity of sound just AFTER it hits a boundary/interface and is returned to transducer
Definition of Transmitted Intensity
Intensity of a sound just AFTER it hits the boundary/interface & continues to travel
Definition of IRC
Intensity Reflection Coefficient, percentage of sound’s intensity that is reflected when it hits a boundary/interface between 2 media
Definition of ITC
Intensity Transmission Coefficient, percentage of sound’s intensity that is transmitted when it hits a boundary/interface between 2 media
Equation for ITC
ITC = 1 - IRC OR 1 = ITC + IRC
All sound must be accounted for!
Requirements for Reflection to Occur (2)
- Sound strikes at 90 °
2. Media must have different acoustic impedances
How does impedance affect reflection?
Greater difference in impedance = more reflection
2 Equations for IRC
IRC = reflected intensity/incident intensity IRC = (Z2 - Z1)^2 / (Z1 + Z2)^2
