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What happens when there are similar impedance values across tissues?
What happens when there are similar impedance values across tissues?
What is calculated using the values for density and speed of ultrasound?
What is calculated using the values for density and speed of ultrasound?
What is the formula to calculate the intensity reflection coefficient?
What is the formula to calculate the intensity reflection coefficient?
What is the result of the intensity reflection coefficient calculation?
What is the result of the intensity reflection coefficient calculation?
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What is incident sound in ultrasound?
What is incident sound in ultrasound?
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What is the density of fat in kg/m3?
What is the density of fat in kg/m3?
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What is the speed of ultrasound in muscle in m/s?
What is the speed of ultrasound in muscle in m/s?
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What is the purpose of calculating acoustic impedance?
What is the purpose of calculating acoustic impedance?
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What type of incidence occurs when the ultrasound path is perpendicular to the boundary?
What type of incidence occurs when the ultrasound path is perpendicular to the boundary?
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What factor contributes to increased absorption of sound energy in a medium?
What factor contributes to increased absorption of sound energy in a medium?
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What is the main condition for specular reflection to occur?
What is the main condition for specular reflection to occur?
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What is the result of the redirection of part of the ultrasound wave back towards the source?
What is the result of the redirection of part of the ultrasound wave back towards the source?
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What is the primary factor influencing the degree of reflection at an interface?
What is the primary factor influencing the degree of reflection at an interface?
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What is the term for the conversion of sound energy into heat within a medium?
What is the term for the conversion of sound energy into heat within a medium?
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What type of reflection occurs when the interface is rough or irregular?
What type of reflection occurs when the interface is rough or irregular?
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What happens to the ultrasound beam in non-specular reflection?
What happens to the ultrasound beam in non-specular reflection?
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What is the primary mechanism of attenuation where ultrasound energy is converted to heat within the tissue?
What is the primary mechanism of attenuation where ultrasound energy is converted to heat within the tissue?
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What is the unit of measurement for attenuation?
What is the unit of measurement for attenuation?
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What is the formula for calculating the total attenuation of ultrasound waves?
What is the formula for calculating the total attenuation of ultrasound waves?
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What type of tissue exhibits low attenuation of ultrasound waves?
What type of tissue exhibits low attenuation of ultrasound waves?
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What is the effect of increasing frequency on ultrasound wave attenuation?
What is the effect of increasing frequency on ultrasound wave attenuation?
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What is the formula for calculating the acoustic impedance of tissue?
What is the formula for calculating the acoustic impedance of tissue?
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What is the unit of measurement for acoustic impedance?
What is the unit of measurement for acoustic impedance?
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What is the result of an acoustic impedance mismatch at tissue interfaces?
What is the result of an acoustic impedance mismatch at tissue interfaces?
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What is the main reason for a more hypoechoic image in diffuse reflection?
What is the main reason for a more hypoechoic image in diffuse reflection?
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What is the term for the reflection of ultrasound waves back to the transducer?
What is the term for the reflection of ultrasound waves back to the transducer?
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What is the condition for refraction to occur?
What is the condition for refraction to occur?
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What is the result of the scattering process?
What is the result of the scattering process?
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What is the term for the image artifacts produced by backscatter?
What is the term for the image artifacts produced by backscatter?
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What is the factor that determines the direction of the refracted beam?
What is the factor that determines the direction of the refracted beam?
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What is the law that defines the refraction of sound waves?
What is the law that defines the refraction of sound waves?
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What is the condition for scattering intensity to increase?
What is the condition for scattering intensity to increase?
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Study Notes
Attenuation of Ultrasound Waves
- Attenuation refers to the progressive reduction in amplitude or intensity of ultrasound waves as they travel through a medium.
- Factors influencing attenuation include path length, frequency, and material properties.
- Attenuation is measured in decibels (dB) and can be calculated using the attenuation coefficient (dB/cm) and path length (cm).
Factors Contributing to Attenuation
- Absorption: the conversion of ultrasound energy into heat within a tissue, influenced by relaxation time and frequency.
- Reflection: the redirection of part of the ultrasound wave back towards the transducer, influenced by acoustic impedance differences between media.
- Scattering: the spreading out of sound waves in different directions, often occurring with rough or irregular surfaces.
Acoustic Impedance and Transmission
- Acoustic impedance (Z) quantifies tissue stiffness and elasticity, calculated as the product of tissue density (ρ) and the speed of sound (C).
- Acoustic impedance mismatch affects transmission and reflection of ultrasound at tissue interfaces.
- Greater transmission occurs when impedance values are similar, while significant differences cause increased reflection.
Incident Sound in Ultrasound
- Incident sound refers to the ultrasound beam before it interacts with a boundary between two different media.
- Types of incidence include normal (perpendicular) and oblique incidence.
- The degree of reflection and refraction is influenced by acoustic impedance differences between the two media.
Factors Contributing to Attenuation: Absorption
- Absorption is influenced by relaxation time and frequency, with higher frequencies producing more heat due to friction and molecular motion.
Factors Contributing to Attenuation: Reflection
- Reflection is more likely to occur when the boundary's dimension is significant relative to the wavelength (large, flat, and smooth boundary).
- Types of ultrasound reflection include specular and non-specular (diffuse) reflection.
Factors Contributing to Attenuation: Scattering
- Scattering refers to the spreading out of sound waves in different directions when they encounter tissues with irregular surfaces or interfaces similar in size to the wavelength of the sound.
- Scattering intensity increases when the tissue interface size is comparable to or smaller than the wavelength of the incident ultrasound wave.
Factors Contributing to Attenuation: Refraction
- Refraction is the change in direction of a sound wave as it passes across a boundary between two different media at an oblique angle.
- Refraction occurs due to differences in propagation speeds of sound in different media, as defined by Snell's Law.
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Description
Measure the reduction in amplitude or intensity of ultrasound waves as they travel through a medium. Factors influencing attenuation include path length and frequency.
