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Physics 3 > Bioeffects > Flashcards

Bioeffects Flashcards

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1
Q

Particle displacement/acoustic pressure

A

Amplitude

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2
Q

What determines the pulse’s amplitude?

A

The pulser

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3
Q

What are the 5 mechanisms of attenuation?

A

Absorption, wavefront divergence, reflection, refraction, scatter

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4
Q

Power =

A

Intensity x area

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5
Q

This is a measure of the total energy transmitted summed over the cross sectional area of the beam per unit time

A

Power

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6
Q

The absolute unit of power

A

Watt (joule/s)

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7
Q

What determines the power?

A

The pulser

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8
Q

Intensity =

A

Power/Area

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9
Q

This is a measure of the strength of a sound wave and is equal to the power per unit area

A

Intensity

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10
Q

The absolute unit of intensity

A

mW/cm2 or W/cm2

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11
Q

If power increases, what happens to intensity?

A

It also increases

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12
Q

If area decreases, what happens to intensity?

A

It increases

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13
Q

What is the relationship between intensity and amplitude?

A

A small change in amplitude will result in a large change to intensity

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14
Q

BUR =

A

SP/SA

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15
Q

A high BUR does what for focus? What is the BUR for a perfectly uniform beam?

A

High BUR = high focus.

BUR would be 1

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16
Q

DF =

A

TA/PA

17
Q

Where does the information on bioeffects come from?

A

Epidemiology, in vitro, animal studies

18
Q

What are the set intensity thresholds for unfocused and focused ultrasound?

A

Unfocused: 100mW/cm2
Focused: 1000mW/cm2 (1 W/cm2)

19
Q

2 main categories for bioeffects

A
  • thermal

- non-thermal (mechanical)

20
Q

Simple oscillation of bubbles that can result in the streaming of liquid resulting in shear stresses

A

Stable cavitation

21
Q

When the bubble actually collapses and produces a shock wave that can result in localized high temperatures and light emission.

A

Transient cavitation

22
Q

What is the thermal index (TI)

A

The amount of acoustic power ended to raise the temperature in tissue 1 degree.
Example, a TI of 2 could possibly raise the temp by 2 degrees

23
Q

TIS, TIB, TIC

A

TIS: soft tissue
TIB: bone near the focus and obstetrics
TIC: bone near the surface (cranial studies)

24
Q

What is the mechanical index (MI)

A

The likelihood that the energy used will lead to cavitation

25
Q

How is MI related to frequency?

A

Inversely proportional to the square root of the frequency.

The frequency would have to quadruple for the MI to halve

26
Q

What are the TI and MI maximums?

A

TI- 6

MI- 1.9

27
Q

The balance between benefit and risk

A

ALARA

28
Q

What tissue is most susceptible to TI?

A

Fetal tissue

Physics 3 (5 decks)

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