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Ultrasound
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A reduction in the intensity of a sound beam to one-half of its orignal value is ____ dB?
-3dB
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A reduction in the intensity of a sound beam to one-quarter of its orignal value is _____dB.
-6dB
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-10 dB means that the intensity is reduced to ____ of its orignal value.
One-tenth
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dB is a mathematical representation with a ___&___ scale.
logarithmic & relative
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True/False. We need one intensity to calculate decibels.
False
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A wave's intensity is 2 mW/cw2. There is a change of +9dB. What is final intensity?
16 mW/cm2
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Every 3 dB change means that the intensity will ______.
Double
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Every 10 dB change means that the intensity will _____________.
Increase ten times
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If the final intensity of a sound beam is more than the initial intensity, then the gain in dB is _____. (+ or -)
Positive
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If the initial intensity of a sound beam is less than the final intensity, then the gain in dB is _______.
Positive
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Name the three components of attenuation.
Absorption, reflection & scattering
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As the path length increases, the attenuation of ultrasound in soft tissue ________.
increases
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Attenuation in lung tissue is [less than, greater than, the same as] attenuation in soft tissue?
greater than
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Attenuation in bone is _______ attenuation in soft tissue.
greater than
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Attenuation in air is ______ attenuation in soft tissue.
greater than
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What are the units of attenuation?
Decibels (dB)
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T or F. In a given medium, attenuation is unrelated to speed of sound.
True (Attenuation & propagation speed are unrelated)
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What is the relationship between ultrasound frequency and the attenuation coefficient in soft tissure?
In soft tissue, the attenuation coeffiecient in dB per centimeter is approx one-half of the ultrasonic frequency in MHz.
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What are the units of the half-value layer thickness?
distance: centimeters
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As frequency decreases, depth of penetration _________.
Increases
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As path length increases, the half boundary layer ______.
remains the same
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Impedence is a characteristic of ______.
Only the medium
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As the path length increases, the attenuation coeffiecient of ultrasound in soft tissue [decreases, remains the same, increases]
remains the same
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Acoustic impedance = _______x_______
Impedance = density (kg/m3) x propagation speed (m/s)
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Two media A and B have the same densities. The speed of sound in medium A is 10% higher than in medium B. Which medium has the higher acoustic impedance?
Medium A's acoustic impedance is higher than medium B's.
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Impedance is important in ______ at boundaries.
Reflections
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Which is better to use while examining a carotid artery, a 7.5 or 3.0 MHz transducer?
The carotid artery is a superficial structure. A 7.5 MHz transducer is better because the higher frequency transducer produces the better image.
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List temporal intensities from largest to smallest.
TP, Imax, PA, TA
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List temporal intensities from smallest to largest.
TA, PA, Imax, TP
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Name the many different names for Axial Resolution.
LARRD. (Longitudinal, Axial, Range, Radial, Depth)
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Normal incidence is also know as?
PORNN (Perpendicular, Orthogonal, Right angle, Ninety degrees, Normal)
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A sound wave with intensity of 50 W/cm2 strikes a boundary and is totally reflected. What is the intensity reflection coefficient?
Since the wave is totally reflected, the intensity reflection coefficient is 100%.
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A sound wave with intensity of 50 W/cm2 strikes a boundary and is totally reflected. What is the intensity reflection coeffiecient?
Since the wave is totally reflected, intensity is 50 w/cm2
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What is the formula for reflection with Normal Incidence?
IRC=(Z2-Z1) / (Z2+Z1) x 100
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What is the formula for transmission with Normal Incidence?
- ITC = 1- IRC
- or ITC = transmitted intensity / incidenct intensity X 100
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What is the conservation of energy concerning coefficients?
100%= IRC+ITC
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Snell's Law defines what?
refraction
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What's the formula for Snell's Law?
Sin (transmission angle) /Sin (incident angle) = Speed of Medium 2/ Speed of Medium 1
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A 2 cm deep reflector has a go-return time of ___microseconds.
26
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A 3 cm deep reflector has a go-return time of ___microseconds.
39
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For every 13 microseconds of go-return time, the object creating the reflection is ___cm deeper in soft tissue.
1 cm
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When the depth of view is shallow, the PRP is ______?
short
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When depth of view is deep, PRP is ______?
long
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What is the PRP when imaging to a depth of 4 cm?
52 microseconds (4x13=52)
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If the PRP is 65 microseconds, what is the max imaging depth?
5 cm (13x5=65)
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