Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
48 Cards in this Set
- Front
- Back
If power doubles and area doubles, what would be the effect on intensity?
|
Since intensity = power / area, the intensity would remain the same.
|
|
If power doubles and area is quadrupled, what would be the effect on intensity?
|
Since intensity = power / area, untensity would be 1/2 its original value.
|
|
If amplitude is decreased by 1/2, what would be the effect on intensity?
|
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.
|
|
If power doubles, and area decreases by 50%, what is the effect on intensity?
|
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
|
|
What is a logarithm?
|
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.
|
|
What are logarithms useful for?
|
Comparing a wide range of values.
|
|
What base is always used for logarithms in ultrasound?
|
10
|
|
What is the log of 2?
|
.3
(Not covered in lecture. I got it from the book, P. 52) |
|
What is a decibel?
|
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
|
|
What are the units of decibels?
|
They are unitless
|
|
What are decibels used for?
|
To compare the ratios of powers, intensities, or amplitudes
|
|
Using the decibel's logarithmic scale, a doubling of power always results in an increase of ____ dB
|
3
|
|
Do decibels represent an absolute value?
|
No, decibels are used to relate to values to each other
|
|
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? |
1. 4x
2. 8x 3. 10x 4. 16x 5. 100x 6. 1,000x 7. 10,000x |
|
What is the power form of the decibel equation?
|
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). |
|
What is the amplitude form of the decibel equation?
|
dB = 20 log (Amplitude final / Amplitude initial)
(Note: Not covered in lecture - I got this from the book, P. 132) |
|
What point is commonly used as a reference point, to define the level of sound represented by 0 dB?
|
The threshold of human hearing.
|
|
Which causes greater attenuation, soft tissues or lungs and bone?
|
Lungs and bone cause greater attenuation, which is why ultrasound is less useful for studying them
|
|
Will "normal" intensity be higher in a focused or unfocused beam?
|
Focused
|
|
Why are focused beams normally not used for vascular studies?
|
Because the areas under study are usually so superficial, the beam can't be focused that close
|
|
What does AIUM stand for?
|
The American Institute of Ultrasound in Medicine
|
|
What is the nature of the AIUM?
|
It is a federal regulatory body, somewhat comparable to the FDA for food and drugs
|
|
What is the maximum intensity value for an unfocused beam, as suggested by the AIUM?
|
100 mw / sq cm
|
|
What is the maximum intensity value for a focused beam, as suggested by the AIUM?
|
1000 mw / sq cm
|
|
What happens in the transducer when color Doppler, or pulse wave Doppler, is activated by the sonographer?
|
Separate beams are activated for each of these, thus increasing the power being directed to the area under study
|
|
Which way of measuring intensity yields the largest value?
|
SPTP (Spatial Peak, Temporal Peak)
|
|
Which way of measuring intensity represents the strongest half pulse in a cycle?
|
Imax
|
|
Which way of measuring intensity is most crucial for measuring bioeffects?
|
SPTA (Spatial Peak, Temporal Average)
|
|
Which way of measuring intensity yields the lowest value?
|
SATA (Spatial Average, Temporal Average)
|
|
To reduce the potential for bioeffects, what should a sonographer ideally do upon freezing an image?
|
Turn the transducer away from the patient, or at least raise it slightly to create an air barrier
|
|
What two factors influence attenuation in soft tissue?
|
1. Frequency of transmitted signal
2. Depth within the tissue |
|
What is the value of the attenuation coefficient?
|
.5 dB / cm / MHz
|
|
With a 4 MHz transducer, how much attenuation would there be for every cm of depth?
|
2 dB
|
|
With a 4 MHz transducer, how much loss would there be at a depth of 2 cm?
|
4 dB
|
|
With a 4 MHz transducer, at approximately which depth would our signal have lost half its original strength?
|
At about 1.5 cm - or, at least, somewhere between 1 and 2 cm.
|
|
Will switching to a lower frequency transducer result in more or less loss due to attenuation?
|
Less
|
|
A recent development in ultrasound is that dermatologists are exploring the idea of diagnosing skin cancers using transducers in what frequency range?
|
20 - 40 MHz
|
|
Transducers transmitting at about what frequency are used for intravascular and intracardiac ultrasound?
|
10 MHz
|
|
Transducers transmitting at about what frequency are used for transvaginal and transrectal ultrasound?
|
7.5 MHz
|
|
Decibel loss is represented by a __1__ sign, and gain is represented by a __2__ sign
|
1. -
2. + |
|
Do "close" or "far" (ie., superficial or deep) returned signals require more gain be applied?
|
Far
|
|
What 3 factors cause attenuation?
|
1. Reflection
2. Scattering 3. Absorption |
|
Which of the 3 attenuation factors is absolutely essential for ultrasound?
|
Reflection
|
|
Define "total gain".
|
The total amplification of all returned signals, regardless of depth.
|
|
What are 2 other names for "total gain"?
|
1. Receiver gain
2. Amplification |
|
What is the term for the depth at which the intensity of sound is reduced 50% from the original?
|
Half value layer thickness
|
|
What is the acronym for half value layer thickness?
|
HVL
|
|
Will switching to a lower frequency transducer increase or decrease the HVL?
|
Increase
|