Term
| What is an every day example of a logarithmic scale? |
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Definition
| The Richter scale which measures the strength of earthquakes. |
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Term
| What are the 3 processes that contribute to attenuation? |
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Definition
1. Reflection
2. Scattering
3. Absorption
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Term
| What are the 2 types of reflection? |
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Definition
1. Specular
2. Diffuse (backscatter)
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Term
| What is the special form of scattering that occurs when the structure's dimensions are much smaller than the beam's wavelength? |
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Definition
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Term
| True or False? Rayleigh scattering increases dramatically with increasing freguency. |
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Definition
True
Rayleigh scattering ȣ Frequency 4
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Term
| What is the significance of attenuation in diagnostic sonography? |
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Definition
| Higher frequency sound attenuates more and is less capable of traveling to substantial depths. |
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Term
| Attenuation is determined by what 2 factors? |
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Definition
1. Path length
2. Frequency of sound
Total Attenuation (dB) =
Atten. Coef. (dB/cm) x Distance (cm) |
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Term
| Distance and attenuation are related how? |
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Definition
Directly.
↑ Distance = ↑ Atteuation
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Term
| Frequency and attenuation are related how? |
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Definition
Directly.
↑ Frequency = ↑ Attenuation
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Term
| What are the 2 intensities that decibels require? |
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Definition
1. Reference (the starting level)
2. The actual level at the time of measurement.
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Term
| Absorption is related to frequency how? |
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Definition
Directly.
↑ Frequency = ↑ Absorption
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Term
| What occurs when ultrasonic energy is converted into another energy form, such as heat? |
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Definition
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Term
| What is the number of decibels of attenuation that occurs when sound travels 1 cm? |
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Definition
Attenuation coefficient.
Atten. Coef. (dB/cm) = F (Mhz)
2
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Term
| What is the advantage of describing sound weakening with an attenuation coefficient? |
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Definition
| Its value (dB/cm) remains constant, regardless of how far the sound travels. |
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Term
Put the following Media in order from lowest attenuation to highest:
1. bone & lung
2. fat
3. air
4. muscle
5. soft tissue
6. water
7. biologic fluids (blood, urine) |
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Definition
1. water
2. biologic fluids (blood, urine)
3. fat
4. soft tissue
5. muscle
6. bone & lung
7. air
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Term
| On what 2 factors does the half-layer value depend? |
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Definition
1. Medium
2. Frequency of sound
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Term
| What is the acoustic resistance to sound traveling in a medium? |
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Definition
Impedance.
Impedance (rayls) = Density (kg/m3) x C (m/s)
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Term
| Of the 3 types of angles, which ones are oblique? |
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Definition
Acute (< 90o)
&
Obtuse (>90o)
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Term
| Perpendicular, Orthogonal, Right Angle, & 90o are all names for what? |
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Definition
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Term
| What are the 3 types of intensities? |
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Definition
1. Incident Intensity
2. Reflected Intensity
3. Transmitted Intensity
*All intensities have units of W/cm2.
Incident (starting) Int. =
Reflected Int. + Transmitted Int. |
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Term
| What is the percentage of the intensity that bounces back when a sound beam strikes the boundary between 2 media? |
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Definition
IRC
Intensity Reflection Coefficient
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Term
| What is the percentage of intensity that passes in the forward direction when the beam strikes an interface between 2 media? |
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Definition
ITC
Intensity Transmission Coefficient
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Term
| In clinical imaging, what percentage of a sound wave's intensity is transmitted at a boundary between 2 soft tissues? |
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Definition
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Term
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Definition
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Term
| The percentage of the incident beam that is reflected is related to what? |
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Definition
| The difference in the impedances of the tissues. |
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Term
| With normal incidence, what formula do you use to calculate the IRC? |
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Definition
|¯Z2 - Z1¯| 2
| Z2 + Z1 | X 100
¯ ¯
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Term
| What is the percentage of the intensity that continues to move forward when the beam reaches a boundary between 2 media? |
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Definition
ITC
Intensity Transmission Coeffcient |
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Term
| The value of the ITC ranges from 0% to 100% and is defined by what formula? |
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Definition
ITC (%) = Transmitted Int. x 100
Incident Int.
OR
ITC (%) = 1 - IRC
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Term
| Which incidence, normal or oblique, can reflections occur even when the impedances of the 2 media are indentical? |
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Definition
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Term
| What are the 2 physical principles that always apply to reflection with oblique incidence? |
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Definition
1. Conservation of energy.
2. Reflection Angle = Incident Angle |
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Term
| What law states that the sum of the percentage of sound reflected and the percentage of sound transmitted must equal 100%? |
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Definition
The law of conservation of energy.
Reflection Coef. + Transmission Coef. = 100% |
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Term
| The angle between the incident sound beam and an imaginary line that is perpendicular to the boundary is called what? |
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Definition
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Term
| The angle between the reflected sound beam and the line perpendicular to the boundary is called what? |
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Definition
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Term
| Transmission with a bend is called what? |
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Definition
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Term
| What 2 conditions must be met for refraction to occur? |
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Definition
1. Oblique incidence.
2. Different propagation speeds of the 2 media. |
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Term
| What is Snell's Law of refraction? |
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Definition
Transmission Angle = Speed of Medium 2
Incident Angle Speed of Medium 1 |
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Term
| How do we identify Medium 1 and Medium 2? |
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Definition
Medium 1 is the medium in which the sound is currently traveling.
Medium 2 is the medium into which the sound is entering. |
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Term
| Under what conditions will the transmission angle be greater than the incident angle? |
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Definition
When the speed of Medium 2 is GREATER than the speed of Medium.
The transmission angle will be less than the incident angle when the speed of Medium 2 is LESS than the speed of Medium 1. |
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