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?

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
What is the reflection coefficient equation?
R=reflected intensity/incident intensity
26
What type of reflect occurs at a perpendicular incidence?
No reflection
27
What reflection occurs at tissues with a large impedance difference?
Full reflection
28
When does scattering occur?
At interaction of small structures such as RBC & capillaries
29
What is Rayleigh scatters?
Reflection of energy equally in all directions
30
If frequency is increased, what happens to scatter?
It increases
31
Describe acoustic impedance
Density of the medium and speed at which sound travels through the medium
32
What is a Rayls?
kg/m2s The unit of specific acoustic impedance
33
What is the equation of acoustic impedance?
z=pxc (tissue density x propagation speed)
34
Define amplitude?
Strength, peak pressure
35
What is the equation for amplitude reflection coefficient?
R=Z2-Z1 / Z2+Z1 (z1=acoustic impedance on proximal side of interface) (z2=acoustic impedance on distal side of interface)
36
What is refraction?
Bending of the soundwave
37
What are the two conditions required for refraction?
1)incident sound wave must not be perpendicular 2)speed of sound must be different on the two sides of the interface
38
What is snell's law equation and what does it predict?
predicts the direction of a transmitted sound beam when refraction occurs. Sin01/c1=sin0t/C2
39
If there is a critical angle, what angle is the transmitted angle?
90 degrees
40
If the transmitted angle is bigger than the critical angle what happens?
Total reflection
41
What is diffraction?
Occurs when a wave passes through an opening or around a barrier
42
What is penetration depth?
At some depth the attenuation is so great the returning US echoes are too weak to be detected
43
What is the round trip attenuation equation?
(ax2pxf)
44
What is the equation for calculating the attenuation when there is a reduction in the intensity?
dB=10 log I/I0
45
What is the difference between speed and velocity?
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
What is compression and rarefaction?
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
What does the following equation show? λ = c/f
the wavelength of the ultrasound (λ) can be calculated by dividing the ultrasound propagation speed (c) by the ultrasound frequency (f).