Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

US Physics > Week 2: Physics of waves > Flashcards

Week 2: Physics of waves Flashcards

You may prefer our related Brainscape-certified flashcards:
Physics 101 flashcards U.S. Geography flashcards AP® Physics flashcards
1
Q

What are the 3 assumptions for imaging modes?

A

1) Axial distance of target from the transducer - given time of arrival
2) Lateral position of target - location/direction of beam
3) Reflection/Scattering strength of target - w/ amplitude

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What are the assumptions of a scanner?

A
  1. C is constant
  2. Beam axis is straight
  3. Attenuation is constant
  4. Pulse travels only to the target and back (along beam axis)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

define a wave?

A
  • Disturbance of regular repeating pattern that travel through space
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Describe transverse waves

A
  • Movement of molecules is 90 degree direction of wave

- Moving waves oscillations are perpendicular to the wave direction

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Describe longitudinal waves

A
  • Sound waves that oscillate back and forth with the particle motion of a medium along the wave direction of propagation (parallel to the direction of wave)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

…. has no net movement of medium (…. and associated….)

A
  1. transverse waves
  2. Disturbance
  3. Energy transported
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Frequency (f) is

A

waves oscillates or crests passing a stationary observer p/sec

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

How is f determined?

A

source of the sound wave e.g. fat, soft tissue

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

what are mechanical waves?

A

a wave that travel via deformable or elastic medium, solids or liquids due to it elastic properties

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Explain this picture

A

This describes compression (increased pressure) and rarefaction (decreased pressure):

1) No movement = rest position
2) Mass is displaced, stretched on one side and compressed on another (storing force & potential energy)
3) The mass is accelerated back to rest with force in the springs gaining kinetic energy while doing so. Carrying past the rest position.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is frequency?

A

of times the ave repeats (oscillation or crests) p/sec

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Anything greater than… is an US wave

A

> 20 Khz

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

define a wavelength?
The equation:
λ = c/f (mm)

A

length or distance between consecutive crests or similar points in the wave (single wave)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Define period? sec

T = 1/f

A

The time required to complete a single cycle (1 wavelength or oscillation)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is Phase?

A

Phase describes the position within a cycle of oscillation and is measured in degrees (or radians, π = 180 ̊)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Describe the term pressure (Pascals)?

1 Pa= 1 N.m-2 (newtons measure of force)

A
  • pressure (p) in a medium oscillates between max & min values as a wave passes
  • Peak +ve pressure: compression (excess pressure)
  • Peak -ve pressure: rarefraction (excess pressure)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

amplitude is described by peak excess … with the … value during the ….. passing

A

1) pressure
2) maximum
3) wave

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What is power?
Energy = Joules (J)
Power = Watts (W)
—> 1 W = 1 J p/sec (s-1)

A

rate at which US energy is produced by the source

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What is displacement amplitude?

A

Max distance moved by a particle from it’s rest position (measure of amplitude (strength) of the wave))

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Whats the difference between actual and normal pressure?

A

is called excess pressure (pressure in the wave)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

Describe how energy plays a role with power?

A

When a wave travels through a medium, it transport energy into that medium from the source.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What is intensity?

W m-2 or Wcm-2

A

measure of the amount of power flowing through a unit area at a 90 degree direction of propagation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

What is intensity associated with?

A

with a wave increases with the pressure amplitude of the wave (I is proportional to pressure squared (p2))

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

what properties determine C?

C = √k/p

A

1) density/P (kg/m3)

2) stiffness/K (Pa)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

What is density?

A

measure of weight of a standard volume of material

26
Q

What is stiffness?

A

how well material resits being deformed

27
Q

what is the normal US f in medical imaging?

A

2-15MHz

28
Q

What is presented with low density and high stifness?

A

high C

29
Q

What is presented with high density and low stiffness?

A

low C

30
Q

What is Z mismatch?

A

sound waves travels into 1 medium hitting an interface with a 2nd medium of different Z values. Some transmitted to 2nd medium, some reflected back to 1st medium

31
Q

What is the IRC equation

A

IRC = Ir / Ii = Pr2 / Pi2 = [Z2-Z1 / Z2 + Z1]2

32
Q

Z abruptly changes at …., ratio of particle…. and particle ….. must also change

A

1) interface
2) pressure
3) velocity

33
Q

However, the particle velocity and …. pressure cannot change abruptly at the interface with …. of medium, therefore must be continuous across interface

A

1) local

2) disruption

34
Q

Why is US gel used?

A

no US would be transmitted

35
Q

What is the equation for specific Z?

A

Z1 = Pi / Vi = Pr / Vr

particle pressure (p) & velocity (v) in incident wave
i = incident
r = reflected
36
Q

What is RA (amplitude reflection coefficient)?

A

ratio of reflected to incident pressure

37
Q

Why is RA important in US imaging?

A

determines the amplitude of echoes produced at bounderies with different tissue types

38
Q

Z in the first medium will be more than Z in the second, true or false?

A

true

Z1 > Z2

39
Q

RA is also described in terms of….. which is the ratio of intensities ….. and ……. waves

A

1) intensity reflection coefficient
2) reflected (Ir)
3) incident (Ii)

40
Q

How would you calculate the intensity transmitted?

A

It = I i - I r

41
Q

With I when flowing through CSA at interface, the energy flow of incident wave must be ….. and …

A

Conversed and split

42
Q

What is this artefact? (image)

A

Reflection artefact

43
Q

explain the principle behind reflection artefact (Law of reflection)?

A

Machine assumes there’s a large interface compared to the wavelength of wave approaching at 90 degrees. with the received and transmitted wave also travelling at 90 degrees

44
Q

… is determined at the interface by … at the interface

A

1) amplitude

2) reflection coefficient

45
Q

What is specular reflection?

A

occurs at a smooth large interface, w/ target greater than the wavelength and angle of reflection is equal to angle of incidence (interface extends to dimensions > than wavelength)

46
Q

Explain diffuse reflection?

A

occurs at rough surface, where target is the scale of a wavelength. The incident wave is reflected over range of angles

47
Q

What is this image (a) showing?

A

Pulse transmitted at a large and smooth interface, angle of incidence is 0 and reflected echo travel back along the same line. A strong echo is received at beam right angle to interface.

48
Q

What is this image (b) showing?

A

The angle of incidence is 10 degrees or more (not 0), therefore the echoes at the interface may not return to the transducer (t=r)

49
Q

What is image (c) showing? gives diffuse reflection

A

A pulse is sent out, reflected is received over multiple angles (pulse waves scattered) on a large, rough interface giving a diffuse reflection. Some of the reflected echos will be received back to the transducer

50
Q

Why does reflection occur?

A

change in acoustic properties (Z)

51
Q

What is a Mirror artefact?

Image here

A
  • occurs due to specular reflection at large smooth interface
  • large reflection coefficient (e.g. tissue-air interface)
  • may occurs if reflected beam encounters scattering target, and are returned along that path to the probe
52
Q

When does Scattering occur?

A

when target is greater than the wavelength

53
Q

What is the correlation between change in Z values and reflection laws when talking about scattering?

A

Parenchyma of most organs, there’s small-scale variations in Z, which can create small-scale reflections (increased scattered echoes).
- Reflections from small targets do not follow laws of reflection

54
Q

What is the Rayleigh Scattering Equation?

A

Ws∝d6f4

d = target size 
f = frequency (f proportional to 1/λ)
Ws = scattered power

(Backscattered power (Ws) is proportional to 6th power of diameter (d) and 4th power of frequency)

55
Q

What is Rayleigh Scattering strongly dependent on?

A
  1. Size of d (target)

2. λ of wave

56
Q

When does Rayleigh scattering occurs?

A

when λ&raquo_space; diameter of scatterer

57
Q

What has a major influence on US image apperance?

A

different tissue types scattering. Stronger backscatter can lead to to a brighter image produced.

58
Q

Give an example of a substance/material property that has a influence on backscatter and why?

A
  • Collagen e.g. increased collagen content repairing post myocardial infarction
  • Blood (RBC, platelets & white blood cells) weak backscatter when compared to other tissue types. RBC &raquo_space; size than λ. Low Z mismatch between RBC and blood fluid
  • -> act as Rayleigh scatters
59
Q

2 important aspects of scattering: 1) US backscattered….. to transducer by small targets are small vs large….. resulting in …. echoes from parenchyma

A

1a) power
1b) interface
1c) weak

60
Q

2) US scattered over a wide angle of …. targets, the final …. does not change with ….. of …… of the wave

A

2a) small
2b) appearance
2c) angle of incidence

61
Q

Are contrast agents affected with scattering?

A

Yes.

But scatter strongly; slightly > size, high Z mismatch between the gas and blood

US Physics (6 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions