Half-intensity depth, and Impedance Flashcards

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1
Q

What is half-intensity depth, (HID)?

A

The depth of tissue that results in 3 dB of attenuation to the intensity.

OR:

The distance sound travels in a tissue that reduces the intensity of sound to one-half its original value.

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2
Q

Name some half-intensity depth synonyms:

A

Penetration depth, depth of penetration, and

half-boundary layer

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3
Q

What are the units of half-intensity depth?

A

Always 3 dB of attenuation

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4
Q

How do you set up an attenuation problem?

A

Set up: Actual attenuation = coefficient x depth x frequency. Then: Solve for unknown.

Ex: dB = 0.5 x cm x MHz

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5
Q

As frequency decreases, depth of penetration ______.

A

Increases

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6
Q

As path length increases, the half boundary

layer _____ __ ____.

A

Remains the same

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7
Q

Impedance is associated with ___ __ _____.

A

Only the medium

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8
Q

As the path length increases, the attenuation coefficient of ultrasound in soft tissue:_______?

[increases, decreases, remains the same].

A

Remains the same

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9
Q

Acoustic impedance = _____ x _____.

A

Impedance (rayls) = density (kg/m3) x propagation speed (m/s)

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10
Q

Impedance is important in _____ at boundaries.

A

Reflections

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11
Q

What is impedance?

A

The acoustic resistance to sound travelling in a medium.

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12
Q

How do you calculate acoustic impedance?

A

Multiply the density of a medium by the speed at which sound travels in the medium.

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13
Q

What are the units of impedance?

A

Rayls. Impedance is often represented by the letter Z.

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14
Q

Impedance is determined by: _____?

A

Medium only.

It is calculated, not measured.

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