Physics: 100504: Decibels, Intensity Measurements, Attenuation, Gain, Hvl

Front 1

If power doubles and area doubles, what would be the effect on intensity?

Back 1

Since intensity = power / area, the intensity would remain the same.

Front 2

If power doubles and area is quadrupled, what would be the effect on intensity?

Back 2

Since intensity = power / area, untensity would be 1/2 its original value.

Front 3

If amplitude is decreased by 1/2, what would be the effect on intensity?

Back 3

Since intensity is proportional to power, and power is proportional to the square of the amplitude, a reduction of the amplitude to 1/2 its original value would result in a reduction in the intensity to 1/4 its original value.

Front 4

If power doubles, and area decreases by 50%, what is the effect on intensity?

Back 4

Since intensity is proportional to power, and intensity is inversely proportional to area, doubling the power while halving the area would have the effect of quadrupling the intensity

Front 5

What is a logarithm?

Back 5

The logarithm of a number in a given base is the power or exponent to which the base must be raised in order to produce that number.

Front 6

What are logarithms useful for?

Back 6

Comparing a wide range of values.

Front 7

What base is always used for logarithms in ultrasound?

Back 7

10

Front 8

What is the log of 2?

Back 8

.3

(Not covered in lecture. I got it from the book, P. 52)

Front 9

What is a decibel?

Back 9

A logarithmic unit of measurement that expresses the magnitude of a physical quantity (usually power or intensity) relative to a specified or implied reference level

Front 10

What are the units of decibels?

Back 10

They are unitless

Front 11

What are decibels used for?

Back 11

To compare the ratios of powers, intensities, or amplitudes

Front 12

Using the decibel's logarithmic scale, a doubling of power always results in an increase of ____ dB

Back 12

3

Front 13

Do decibels represent an absolute value?

Back 13

No, decibels are used to relate to values to each other

Front 14

What power increases are represented by decibel increases of:

1. 6 dB?

2. 9 dB?

3. 10 dB?

4. 12 dB?

5. 20 dB?

6. 30 dB?
7. 40 dB?

Back 14

1. 4x

2. 8x

3. 10x

4. 16x

5. 100x
6. 1,000x
7. 10,000x

Front 15

What is the power form of the decibel equation?

Back 15

dB = 10 log (Power final / Power initial)

Note: This is mentioned in passing in slide #39, but was not really focused on in lecture. So for the most part, I got this from the book, P. 130).

Front 16

What is the amplitude form of the decibel equation?

Back 16

dB = 20 log (Amplitude final / Amplitude initial)

(Note: Not covered in lecture - I got this from the book, P. 132)

Front 17

What point is commonly used as a reference point, to define the level of sound represented by 0 dB?

Back 17

The threshold of human hearing.

Front 18

Which causes greater attenuation, soft tissues or lungs and bone?

Back 18

Lungs and bone cause greater attenuation, which is why ultrasound is less useful for studying them

Front 19

Will "normal" intensity be higher in a focused or unfocused beam?

Back 19

Focused

Front 20

Why are focused beams normally not used for vascular studies?

Back 20

Because the areas under study are usually so superficial, the beam can't be focused that close

Front 21

What does AIUM stand for?

Back 21

The American Institute of Ultrasound in Medicine

Front 22

What is the nature of the AIUM?

Back 22

It is a federal regulatory body, somewhat comparable to the FDA for food and drugs

Front 23

What is the maximum intensity value for an unfocused beam, as suggested by the AIUM?

Back 23

100 mw / sq cm

Front 24

What is the maximum intensity value for a focused beam, as suggested by the AIUM?

Back 24

1000 mw / sq cm

Front 25

What happens in the transducer when color Doppler, or pulse wave Doppler, is activated by the sonographer?

Back 25

Separate beams are activated for each of these, thus increasing the power being directed to the area under study

Front 26

Which way of measuring intensity yields the largest value?

Back 26

SPTP (Spatial Peak, Temporal Peak)

Front 27

Which way of measuring intensity represents the strongest half pulse in a cycle?

Back 27

Imax

Front 28

Which way of measuring intensity is most crucial for measuring bioeffects?

Back 28

SPTA (Spatial Peak, Temporal Average)

Front 29

Which way of measuring intensity yields the lowest value?

Back 29

SATA (Spatial Average, Temporal Average)

Front 30

To reduce the potential for bioeffects, what should a sonographer ideally do upon freezing an image?

Back 30

Turn the transducer away from the patient, or at least raise it slightly to create an air barrier

Front 31

What two factors influence attenuation in soft tissue?

Back 31

1. Frequency of transmitted signal
2. Depth within the tissue

Front 32

What is the value of the attenuation coefficient?

Back 32

.5 dB / cm / MHz

Front 33

With a 4 MHz transducer, how much attenuation would there be for every cm of depth?

Back 33

2 dB

Front 34

With a 4 MHz transducer, how much loss would there be at a depth of 2 cm?

Back 34

4 dB

Front 35

With a 4 MHz transducer, at approximately which depth would our signal have lost half its original strength?

Back 35

At about 1.5 cm - or, at least, somewhere between 1 and 2 cm.

Front 36

Will switching to a lower frequency transducer result in more or less loss due to attenuation?

Back 36

Less

Front 37

A recent development in ultrasound is that dermatologists are exploring the idea of diagnosing skin cancers using transducers in what frequency range?

Back 37

20 - 40 MHz

Front 38

Transducers transmitting at about what frequency are used for intravascular and intracardiac ultrasound?

Back 38

10 MHz

Front 39

Transducers transmitting at about what frequency are used for transvaginal and transrectal ultrasound?

Back 39

7.5 MHz

Front 40

Decibel loss is represented by a __1__ sign, and gain is represented by a __2__ sign

Back 40

1. -
2. +

Front 41

Do "close" or "far" (ie., superficial or deep) returned signals require more gain be applied?

Back 41

Far

Front 42

What 3 factors cause attenuation?

Back 42

1. Reflection
2. Scattering
3. Absorption

Front 43

Which of the 3 attenuation factors is absolutely essential for ultrasound?

Back 43

Reflection

Front 44

Define "total gain".

Back 44

The total amplification of all returned signals, regardless of depth.

Front 45

What are 2 other names for "total gain"?

Back 45

1. Receiver gain
2. Amplification

Front 46

What is the term for the depth at which the intensity of sound is reduced 50% from the original?

Back 46

Half value layer thickness

Front 47

What is the acronym for half value layer thickness?

Back 47

HVL

Front 48

Will switching to a lower frequency transducer increase or decrease the HVL?

Back 48

Increase