# Shared Flashcard Set

## Details

Understanding Ultrasound Physics Ch.6
Ultrasound Physics Ch. 6 Chapter Questions
38
Physics
Not Applicable
05/04/2016

Term
 What is an every day example of a logarithmic scale?
Definition
 The Richter scale which measures the strength of earthquakes.
Term
 What are the 3 processes that contribute to attenuation?
Definition
 1. Reflection 2. Scattering 3. Absorption
Term
 What are the 2 types of reflection?
Definition
 1. Specular 2. Diffuse (backscatter)
Term
 What is the special form of scattering that occurs when the structure's dimensions are much smaller than the beam's wavelength?
Definition
 Rayleigh scattering
Term
 True or False? Rayleigh scattering increases dramatically with increasing freguency.
Definition
 True Rayleigh scattering ȣ Frequency 4
Term
 What is the significance of attenuation in diagnostic sonography?
Definition
 Higher frequency sound attenuates more and is less capable of traveling to substantial depths.
Term
 Attenuation is determined by what 2 factors?
Definition
 1. Path length 2. Frequency of sound   Total Attenuation (dB) = Atten. Coef. (dB/cm) x Distance (cm)
Term
 Distance and attenuation are related how?
Definition
 Directly. ↑ Distance   =   ↑ Atteuation
Term
 Frequency and attenuation are related how?
Definition
 Directly. ↑  Frequency  =  ↑  Attenuation
Term
 What are the 2 intensities that decibels require?
Definition
 1. Reference (the starting level) 2. The actual level at the time of measurement.
Term
 Absorption is related to frequency how?
Definition
 Directly. ↑  Frequency  =  ↑  Absorption
Term
 What occurs when ultrasonic energy is converted into another energy form, such as heat?
Definition
 Absorption.
Term
 What is the number of decibels of attenuation that occurs when sound travels 1 cm?
Definition
 Attenuation coefficient.   Atten. Coef. (dB/cm) =   F (Mhz)                              2
Term
 What is the advantage of describing sound weakening with an attenuation coefficient?
Definition
 Its value (dB/cm) remains constant, regardless of how far the sound travels.
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)
Definition
 1. water 2. biologic fluids (blood, urine) 3. fat 4. soft tissue 5. muscle 6. bone & lung 7. air
Term
 On what 2 factors does the half-layer value depend?
Definition
 1. Medium 2. Frequency of sound
Term
 What is the acoustic resistance to sound traveling in a medium?
Definition
 Impedance.   Impedance (rayls)  =  Density (kg/m3)  x  C (m/s)
Term
 Of the 3 types of angles, which ones are oblique?
Definition
 Acute (< 90o) & Obtuse (>90o)
Term
 Perpendicular, Orthogonal, Right Angle, & 90o are all names for what?
Definition
 Normal Incidence
Term
 What are the 3 types of intensities?
Definition
 1. Incident Intensity 2. Reflected Intensity 3. Transmitted Intensity  *All intensities have units of W/cm2.   Incident (starting) Int. = Reflected Int. + Transmitted Int.
Term
 What is the percentage of the intensity that bounces back when a sound beam strikes the boundary between 2 media?
Definition
 IRC Intensity Reflection Coefficient
Term
 What is the percentage of intensity that passes in the forward direction when the beam strikes an interface between 2 media?
Definition
 ITC Intensity Transmission Coefficient
Term
 In clinical imaging, what percentage of a sound wave's intensity is transmitted at a boundary between 2 soft tissues?
Definition
 99% or more.
Term
 IRC (%) + ITC (%) = ?
Definition
 100%
Term
 The percentage of the incident beam that is reflected is related to what?
Definition
 The difference in the impedances of the tissues.
Term
 With normal incidence, what formula do you use to calculate the IRC?
Definition
 |¯Z2  -   Z1¯| 2   |   Z2 + Z1   |     X   100    ¯              ¯
Term
 What is the percentage of the intensity that continues to move forward when the beam reaches a boundary between 2 media?
Definition
 ITC Intensity Transmission Coeffcient
Term
 The value of the ITC ranges from 0% to 100% and is defined by what formula?
Definition
 ITC (%) = Transmitted Int.   x  100 Incident Int. OR ITC (%) = 1 - IRC
Term
 Which incidence, normal or oblique, can reflections occur even when the impedances of the 2 media are indentical?
Definition
 Oblique.
Term
 What are the 2 physical principles that always apply to reflection with oblique incidence?
Definition
 1. Conservation of energy. 2. Reflection Angle = Incident Angle
Term
 What law states that the sum of the percentage of sound reflected and the percentage of sound transmitted must equal 100%?
Definition
 The law of conservation of energy.   Reflection Coef. + Transmission Coef. = 100%
Term
 The angle between the incident sound beam and an imaginary line that is perpendicular to the boundary is called what?
Definition
 Angle of Incidence.
Term
 The angle between the reflected sound beam and the line perpendicular to the boundary is called what?
Definition
 Angle of Reflection.
Term
 Transmission with a bend is called what?
Definition
 Refraction.
Term
 What 2 conditions must be met for refraction to occur?
Definition
 1. Oblique incidence. 2. Different propagation speeds of the 2 media.
Term
 What is Snell's Law of refraction?
Definition
 Transmission Angle = Speed of Medium 2      Incident Angle         Speed of Medium 1
Term
 How do we identify Medium 1 and Medium 2?
Definition
 Medium 1 is the medium in which the sound is currently traveling.   Medium 2 is the medium into which the sound is entering.
Term
 Under what conditions will the transmission angle be greater than the incident angle?
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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