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MEDIMAGE717 > Physics Principles of Diagnostic Ultrasound > Flashcards

Physics Principles of Diagnostic Ultrasound Flashcards

1
Q

Describe attenuation

A

As ultrasound waves travel through tissue it becomes progressively weaker

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2
Q

How do we calculate attenuation?

A

a=(db/cm)xd

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3
Q

As amplitude is decreased, what happens to intensity?

A

It decreases

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4
Q

If there is an increase in frequency, what happens to attenuation?

A

It increases

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5
Q

What is transverse?

A

Medium moves perpendicular to direction of the wave

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6
Q

What is longitudinal?

A

Medium moves parallel to the wave

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7
Q

What is compression?

A

Transducer moves towards the body and compresses tissue
*highest pressure of soundwave

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8
Q

What is rarefaction?

A

Transducer moves away from the body and decompresses tissue
*smallest point of pressure of soundwave

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9
Q

What is propagation speed?

A

The speed of the ultrasound waves through tissue

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10
Q

What speed does the machine think soft tissue is?

A

1540m/s

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11
Q

What is the frequency of sound waves?

A

Number of times per second

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12
Q

What is amplitude?

A

Peak pressure

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13
Q

What is intensity?

A

Power per unit in the wave

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14
Q

As frequency increases what happens to the wavelength?

A

It decreases

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15
Q

As the wavelength decreases what happens to the resolution?

A

It is enhanced

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16
Q

What is the wavelength?

A

The wavelength is the distance between one peak of the wave and the next peak

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17
Q

What is absorption?

A

Acoustic energy lost in the medium because it is converted into heat

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18
Q

What 3 things is absorption determined by?

A

1) viscosity of the medium
2) relaxation time of the medium
3) frequency of the sound

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19
Q

What is propagation speed?

A

Speed of sound affected by the density and elasticity of the medium it is travelling through

20
Q

Is propagation speed higher in bone or air?

A

Bone

21
Q

What is reflection?

A

Interaction of ultrasound with relatively large and smooth surfaces

22
Q

What 3 things does reflection depend on?

A

1) acoustic properties of two tissues
2) angle of incidence
3) reflecting surface

23
Q

What is specular reflector?

A

strong echoes

24
Q

What is non-specular reflector?

A

Weak echoes

25
Q

What is the reflection coefficient equation?

A

R=reflected intensity/incident intensity

26
Q

What type of reflect occurs at a perpendicular incidence?

A

No reflection

27
Q

What reflection occurs at tissues with a large impedance difference?

A

Full reflection

28
Q

When does scattering occur?

A

At interaction of small structures such as RBC & capillaries

29
Q

What is Rayleigh scatters?

A

Reflection of energy equally in all directions

30
Q

If frequency is increased, what happens to scatter?

A

It increases

31
Q

Describe acoustic impedance

A

Density of the medium and speed at which sound travels through the medium

32
Q

What is a Rayls?

A

kg/m2s
The unit of specific acoustic impedance

33
Q

What is the equation of acoustic impedance?

A

z=pxc
(tissue density x propagation speed)

34
Q

Define amplitude?

A

Strength, peak pressure

35
Q

What is the equation for amplitude reflection coefficient?

A

R=Z2-Z1 / Z2+Z1
(z1=acoustic impedance on proximal side of interface)
(z2=acoustic impedance on distal side of interface)

36
Q

What is refraction?

A

Bending of the soundwave

37
Q

What are the two conditions required for refraction?

A

1)incident sound wave must not be perpendicular
2)speed of sound must be different on the two sides of the interface

38
Q

What is snell’s law equation and what does it predict?

A

predicts the direction of a transmitted sound beam when refraction occurs.

Sin01/c1=sin0t/C2

39
Q

If there is a critical angle, what angle is the transmitted angle?

A

90 degrees

40
Q

If the transmitted angle is bigger than the critical angle what happens?

A

Total reflection

41
Q

What is diffraction?

A

Occurs when a wave passes through an opening or around a barrier

42
Q

What is penetration depth?

A

At some depth the attenuation is so great the returning US echoes are too weak to be detected

43
Q

What is the round trip attenuation equation?

A

(ax2pxf)

44
Q

What is the equation for calculating the attenuation when there is a reduction in the intensity?

A

dB=10 log I/I0

45
Q

What is the difference between speed and velocity?

A

Speed refers to an object’s change in distance with respect to time, whereas velocity refers to an object’s change in displacement with respect to time.

46
Q

What is compression and rarefaction?

A

compressions are regions of high pressure due to particles being close together. rarefactions are regions of low pressure due to particles being spread further apart

47
Q

What does the following equation show?
λ = c/f

A

the wavelength of the
ultrasound (λ) can be calculated by dividing the ultrasound propagation
speed (c) by the ultrasound frequency (f).

MEDIMAGE717 (8 decks)

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