Physics: 100427: Power, Intensity, Interference, Acoustic Variables, Amplitude, Acoustic Paramenters

Front 1

In ultrasound, how is "loudness" (aka volume, aka amplitude) controlled?

Back 1

By the "power" button on the machine.

Front 2

Is amplitude operator-dependent or operator-independent?

Back 2

Operator-dependent

Front 3

What are the two types of ultrasound?

Back 3

1. Diagnostic
2. Theraputic

Front 4

What are two typical uses of theraputic ultrasound?

Back 4

1. To destroy kidney stones
2. To remove fat

Front 5

In diagnostic ultrasound, the power level we use is about what fraction of the maximum potential destructive force which ultrasound is capable of?

Back 5

1 / 1,000

Front 6

What are 2 ways of improving an ultrasound image?

Back 6

1. By transmitting the signals at higher power
2. By manipulating the received (echoed) signals

Front 7

What principle is used to govern the power setting using in ultrasound?

Back 7

The ALARA Principle (As Low As Reasonably Achievable)

Front 8

To be consistent with the ALARA principle, a good sonographer manipulates ____ signals, not ____ signals.

Back 8

1. Received
2. Transmitted

Front 9

An example of a received signal which the sonographer can manipulate is ____.

Back 9

Gain (including the TGC slider controls)

Front 10

An example of a transmitted signal (which the sonographer should not manipulate to a significant extent) is _____.

Back 10

Power

Front 11

What are the units of power?

Back 11

Watts

Front 12

What additional information is needed for us to place a particular level of power in perspective?

Back 12

The size of the area over which that power is being applied

Front 13

Intensity =

Back 13

Power / Area

Front 14

What is the "sector"?

Back 14

The imaging area - the area being exposed to the ultrasound beam

Front 15

What are typical units for intensity?

Back 15

Watts / sq. cm

Front 16

At a constant power, decreasing the area of the sector will have the effect of increasing the _____.

Back 16

Intensity

Front 17

When 2 sounds have a frequency difference of less than _ Hz, most people hear it as one sound

Back 17

7

Front 18

Frequencies in certain ratios create _____ sensations.

Back 18

pleasing

Front 19

What is stated by Huygen's Principle?

Back 19

When 2 waves meet in a medium, the resulting interference causes the medium to take on a shape resulting from the effect of each individual wave.

Front 20

What is interference?

Back 20

A reaction to 2 or more waves

Front 21

What type of interference occurs if two waves meet in such a fashion that their crests (or troughs) coincide?

Back 21

Constructive interference

Front 22

What type of interference occurs if two waves meet in such a fashion that the crest of one coincides with the trough of the other?

Back 22

Destructive interference

Front 23

When two waves engage in "constructive interference", they are said to be _____.

Back 23

In phase

Front 24

When two waves engage in "destructive interference", they are said to be _____.

Back 24

Out of phase

Front 25

What is sound?

Back 25

A traveling variation of acoustic variables.

Front 26

What is an "acoustic variable"?

Back 26

The acoustic variables are pressure, density, and particle motion. These undergo transient cyclic changes when a sound occurs.

Front 27

What technology is used to eliminate the potential for constructive or destructive interference between the transmitted and received signals?

Back 27

Pulse technology, which involves pausing between sets of transmitted signals to allow time for the echoes to return without encountering interference from the next set of transmitted signals.

Front 28

A region of high acoustic variables is called an area of _____.

Back 28

Compression

Front 29

A region of low acoustic variables is called an area of ______.

Back 29

Rarefaction

Front 30

What is amplitude (in terms of actual physical conditions)?

Back 30

The amount of change in a varying quantity over time. The quantity in question can be any of pressure, density, or particle motion.

Front 31

What is amplitude (in terms of graphic representation)?

Back 31

The maximum variation from normal resting or baseline level (of pressure, density, or particle motion) to the peak

Front 32

The units used to measure amplitude depend on which ______ is being measured.

Back 32

acoustic variable

Front 33

Amount of pressure increase or decrease is called ________.

Back 33

Pressure amplitude

Front 34

What are the units of pressure, or pressure amplitude?

Back 34

pascals (Pa) or megapascals (MPa)

Front 35

What are the units of density, or density amplitude?

Back 35

grams / cubic cm

Front 36

The difference between maximum and minimum (peak to trough) values of an acoustic variable is called the ______.

Back 36

Peak to peak amplitude

Front 37

What are the units of motion (distance), or motion (distance) amplitude?

Back 37

cm

Front 38

Peak to peak amplitude =

Back 38

2 x amplitude

Front 39

Half of the peak to peak amplitude is simply called ______.

Back 39

Amplitude

Front 40

If the "resting" value is 5, the "compressed" value is 15, and the "rarefied" value is -5, then the amplitude is _1_, and the peak to peak amplitude is _2_.

Back 40

1. 10
2. 20

Front 41

The more power used, the higher the _____.

Back 41

Amplitude

Front 42

As sound passes through a medium, the _____ of the sound decreases.

Back 42

Amplitude

Front 43

Weakening of a wave is called _____.

Back 43

Attenuation

Front 44

The rate at which work is done is called _____.

Back 44

Power

Front 45

As sound propagates through the body, power ______.

Back 45

Decreases

Front 46

How is power related to amplitude?

Back 46

Power is proportional to (Amplitude) ** 2

Front 47

What determines the power?

Back 47

Initially, by the sound source (the ultrasound machine), which is controlled by the operator - then, as it propagates, by the body tissues

Front 48

Can the sonographer change the power?

Back 48

Yes, but (s)he should refrain from setting it to 100%

Front 49

How are intensity and area related?

Back 49

Inversely. Since Intensity = Power / Area, as area decreases, intensity increases.

Front 50

How are power and intensity related?

Back 50

Directly. Since Intensity = Power / Area, as power increases, so does intensity.

Front 51

Who determines intensity?

Back 51

The source (the ultrasound machine) and the imaging area

Front 52

How are amplitude, power, and intensity related?

Back 52

Directly, since Power = Amplitude **2, and Intensity = Power / Area

Front 53

What are acoustic parameters?

Back 53

"Acoustic parameter" is a more general term than "acoustic variable". It includes the acoustic variables, and any other variable involved in making sound, including frequency, wavelength, period, power, intensity, propagation speed, etc.

Front 54

How is intensity related to amplitude?

Back 54

Intensity is proportional to amplitude **2.