Ultrasound Attenuation

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Questions and Answers

What happens when there are similar impedance values across tissues?

Transmission decreases

Impedance mismatch increases

Transmission is greater (correct)

Reflection increases

What is calculated using the values for density and speed of ultrasound?

Speed of ultrasound

Acoustic impedance (correct)

Intensity reflection coefficient

Density of a medium

What is the formula to calculate the intensity reflection coefficient?

(Z1+Z2)2 ÷ (Z1-Z2)2

(Z2-Z1)2 ÷ (Z1+Z2)2 (correct)

(Z1-Z2)2 ÷ (Z2+Z1)2

(Z1+Z2)2 ÷ (Z2-Z1)2

What is the result of the intensity reflection coefficient calculation?

2.9% Signup and view all the answers

What is incident sound in ultrasound?

The ultrasound beam before it interacts with a boundary Signup and view all the answers

What is the density of fat in kg/m3?

925 Signup and view all the answers

What is the speed of ultrasound in muscle in m/s?

1590 Signup and view all the answers

What is the purpose of calculating acoustic impedance?

To calculate the intensity reflection coefficient Signup and view all the answers

What type of incidence occurs when the ultrasound path is perpendicular to the boundary?

Normal Incidence Signup and view all the answers

What factor contributes to increased absorption of sound energy in a medium?

Slower molecular relaxation Signup and view all the answers

What is the main condition for specular reflection to occur?

Large and smooth interface Signup and view all the answers

What is the result of the redirection of part of the ultrasound wave back towards the source?

Reflection Signup and view all the answers

What is the primary factor influencing the degree of reflection at an interface?

Acoustic impedance difference Signup and view all the answers

What is the term for the conversion of sound energy into heat within a medium?

Absorption Signup and view all the answers

What type of reflection occurs when the interface is rough or irregular?

Diffuse Reflection Signup and view all the answers

What happens to the ultrasound beam in non-specular reflection?

It is scattered in multiple directions Signup and view all the answers

What is the primary mechanism of attenuation where ultrasound energy is converted to heat within the tissue?

Absorption Signup and view all the answers

What is the unit of measurement for attenuation?

Decibels (dB) Signup and view all the answers

What is the formula for calculating the total attenuation of ultrasound waves?

Total attenuation (dB) = Attenuation Coefficient (dB/cm) x Path length (cm) Signup and view all the answers

What type of tissue exhibits low attenuation of ultrasound waves?

Fluids Signup and view all the answers

What is the effect of increasing frequency on ultrasound wave attenuation?

It increases the attenuation Signup and view all the answers

What is the formula for calculating the acoustic impedance of tissue?

Z = ρ x C Signup and view all the answers

What is the unit of measurement for acoustic impedance?

Rayls (1 rayl = 1 kg/(m²·s)) Signup and view all the answers

What is the result of an acoustic impedance mismatch at tissue interfaces?

Increased reflection of ultrasound waves Signup and view all the answers

What is the main reason for a more hypoechoic image in diffuse reflection?

The less uniform tissue Signup and view all the answers

What is the term for the reflection of ultrasound waves back to the transducer?

Backscatter Signup and view all the answers

What is the condition for refraction to occur?

The speed of sound must differ between the two media Signup and view all the answers

What is the result of the scattering process?

The reflection of sound waves in different directions Signup and view all the answers

What is the term for the image artifacts produced by backscatter?

Speckle Signup and view all the answers

What is the factor that determines the direction of the refracted beam?

The speed of sound in the second medium Signup and view all the answers

What is the law that defines the refraction of sound waves?

Snell's Law Signup and view all the answers

What is the condition for scattering intensity to increase?

The tissue interface size is comparable to or smaller than the wavelength of the sound wave Signup and view all the answers

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.