Chapter 2 Ultrasound - Notes 2

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1

Incident beam

starting beam

2

Reflected beam

after the incident beam hits a border part of the beam is reflected back

3

transmitted beam

after the incident beam hits a border part of the beam is transmitted through the next medium

4

Reflected angle

the angle in which the beam is reflected back

reflected angle = incident angle

5

What does the intensity of the reflected beam depend on?

incident beam

6

impedance formula

impedance = density * speed

7

Impedance

resistance to sound traveling through the medium.

8

What is likely when turning up output gain?

tissue damage

9

impedance symbol

z

10

Impedance units

rayl

11

What is the relationship between impedance and propagation speed?

directly

12

What is the relationship between impedance and density?

directly

13

IRC

% of the beam that is reflected back to the transducer

14

IRC formula 1

IRC = Reflected Intensity/ Incident Intensity

IRC - Ri/Ii

15

IRC formula 2

[(z2 - z1) / (z2 + z1)] squared

16

ITC

% of the beam that is transmitted through the medium

17

ITC formula 2

ITC = Transmitted Intensity/ Incident Intensity

ITC - Ti/Ii

18

IRC + ITC =

A) 0%
B) 1%
C) 1
D) 0 dB
E) 10 dB

C) 1

19

other names for 90 degrees

perpendicular
orthogonal
right angle
Normal

20

Impedance relationship with IRC

direct

21

Bone will always appear _________ due to high impedance mismatch

A) brighter
B) darker

A) brighter

22

Refraction

change of direction of the sound wave as it passes from one medium to another.

23

Refraction transmission angle

angle of transmission depends on change in propagation speed that exists between two media

24

Snells law

Sine i/ sine r = speed i / speed r

25

Snell's law 2

(New c / old c) * old angle = new angle

26

Is the angle higher or lower if the new speed is slower?

lower

27

Specular Reflections

when sound waves hit a large smooth surface at 90 degrees

bladder and vessels

28

Diffusion

boundary is not smooth

boundary smaller than the wavelength.

Light gets scattered (random and disorganized)

29

Scattering

non-specular reflection occurs at small, irregular of rough interfaces

It is not angle dependent

30

Relationship between frequency and scatter

directly related

31

Positive effects of scattering

scattering makes echo reception less dependent on incident angle

allows visualization of boundaries which specular reflection angle would miss

32

Effects of scatter

Two waves arriving at the same time either reinforce of cancel each other.

33

Negative effects of scattering

grainy images

34

Range equation

d = 1/2 ct

Distance can not be measured but time can if speed is known

How machine places image

35

How long will it take for u/s to detect a mass at a depth of 1 cm?

13 cm

36

More Amplitude

brighter dot.