Lecture 6

Question 1

What happens to sound at the boundaries when sound is transmitted?

Answer 1

It passes through and continues on

Question 2

Definition of Reflection

Answer 2

Sound bounces back to the transducer

Question 3

Definition of Scatter

Answer 3

Sound is sent in different directions

Question 4

Definition of Refraction

Answer 4

Sound beam is bent and sent in a different direction

Question 5

Scattering occurs more frequently in tissue that is (homogenous/heterogenous)

Answer 5

Heterogenous

Question 6

Definition of Specular Reflection

Answer 6

Reflection off a large, smooth boundary

Question 7

How does the sound beam occur in specular reflection?

Answer 7

Perpendicular

Question 8

Synonyms for Specular Reflection

Answer 8

Normal, orthogonal, 90 degree incidence, right angle incidence

Question 9

A sound beam will be _____ or _____ when coming in at a 90 degree angle

Answer 9

Reflected or transmitted

Question 10

Backscatter

Answer 10

Sound returns to transducer from a non-specular reflector

Question 11

Definition of Non-Specular Reflection

Answer 11

Reflection from large, rough surfaces

Question 12

(T/F) Scattering occurs when the reflector is smaller than the SPL

Answer 12

False, scattering occurs when the reflector is smaller than the wavelength

Question 13

Which is stronger? Reflection from a non-specular reflector or specular reflector?

Answer 13

Specular reflection is stronger b/c the boundary is smooth, reducing scatter

Question 14

Definition of Rayleigh Scattering

Answer 14

Sound is redirected in all directions due to the small size of the reflector ( < wavelength). Weakest return to probe

Question 15

What reflectors in the human body produce Rayleigh scattering?

Answer 15

Red blood cells

Question 16

Which modality is most affected by Rayleigh scattering?

Answer 16

Doppler

In Doppler, sound beams are reflected off of red blood cells whereas in ultrasound, the beams are reflected off tissue.

Question 17

(T/F) Rayleigh scatter is not affected by frequency

Answer 17

False, directly related to Rayleigh scattering.

Frequency ↑, scattering ↑

Question 18

Definition of Incident Sound

Answer 18

Sound that is coming from the sound source & going into the medium (BEFORE boundary)

Question 19

Definition of Transmitted Sound

Answer 19

Sound that continues to propagate in the direction it was going AFTER hitting a boundary

Question 20

Definition of Reflected Sound

Answer 20

Sound that is RETURNED to transducer after hitting boundary

Question 21

Equation for Incident Sound

Answer 21

Incident sound = transmitted sound + reflected sound

Question 22

Definition of Incident Intensity

Answer 22

Intensity of a sound BEFORE hitting a boundary/interface

Question 23

Definition of Reflected Intensity

Answer 23

Intensity of sound just AFTER it hits a boundary/interface and is returned to transducer

Question 24

Definition of Transmitted Intensity

Answer 24

Intensity of a sound just AFTER it hits the boundary/interface & continues to travel

Question 25

Definition of IRC

Answer 25

Intensity Reflection Coefficient, percentage of sound’s intensity that is reflected when it hits a boundary/interface between 2 media

Question 26

Definition of ITC

Answer 26

Intensity Transmission Coefficient, percentage of sound’s intensity that is transmitted when it hits a boundary/interface between 2 media

Question 27

Equation for ITC

Answer 27

ITC = 1 - IRC OR 1 = ITC + IRC

All sound must be accounted for!

Question 28

Requirements for Reflection to Occur (2)

Answer 28

1. Sound strikes at 90 °

2. Media must have different acoustic impedances

Question 29

How does impedance affect reflection?

Answer 29

Greater difference in impedance = more reflection

Question 30

2 Equations for IRC

Answer 30

IRC = reflected intensity/incident intensity
IRC  = (Z2 - Z1)^2 / (Z1 + Z2)^2