24 Questions
What is the primary reason for a more hypoechoic image in diffuse reflection?
Less return of reflected sound waves
What type of reflection is responsible for the bright signal in the sonogram of bone tissue?
Specular reflection
What is the result of backscatter in ultrasound imaging?
Image artifacts called 'speckle'
What is the condition for refraction to occur?
The sound wave hits the boundary at an angle that is not 90 degrees
What is the primary mechanism of attenuation where ultrasound energy is converted to heat within the tissue?
Absorption
What determines the direction of the refracted beam?
The speed of sound in the second medium relative to the first medium
What is the unit of measurement for attenuation in ultrasound?
Decibels
What is the formula for calculating the total attenuation of ultrasound waves?
Total attenuation (dB) = Attenuation Coefficient (dB/cm) x Path length (cm)
What is the name of the law that defines the refraction of sound waves?
Snell's Law
What is the result of scattering intensity increasing?
An increase in image artifacts
What is the result of acoustic impedance mismatch at tissue interfaces?
Increased reflection of ultrasound
What type of tissue exhibits low attenuation of ultrasound waves?
Fluids
What is the requirement for scattering to occur?
The tissue interface size must be comparable to or smaller than the wavelength
What is the formula for calculating acoustic impedance?
Z = ρ x C
What is the effect of path length on ultrasound attenuation?
Increased path length results in more attenuation
What is the effect of frequency on ultrasound attenuation?
Higher frequencies undergo more attenuation
Which type of wave requires a physical medium to propagate?
Mechanical Waves
What is the primary difference between longitudinal and transverse waves?
The direction of particle displacement
What is the speed of electromagnetic waves in a vacuum?
Approximately 299,792.456.2 m/s
What is the definition of frequency in sound waves?
The number of complete cycles per second
What is an example of a mechanical wave?
Ocean wave
What is the characteristic of longitudinal waves?
Particle displacement occurs parallel to the wave's direction of energy movement
What is an example of an electromagnetic wave?
X-ray
What are the key parameters to consider in sound waves?
Frequency, Amplitude, Power, Intensity
Study Notes
Classification of Waves
- Mechanical Waves: defined by the disturbance of a physical medium, examples include ocean waves, sound waves, and seismic waves
- Electromagnetic Waves: do not require a medium and can propagate through a vacuum, examples include radio waves, X-rays, and light
Wave Types
- Longitudinal Waves: particle displacement occurs parallel to the wave's direction of energy movement
- Transverse Waves: particle displacement occurs perpendicular to the wave's direction of propagation, velocity is relatively constant at approximately 299,792.456.2 m/s in a vacuum (speed of light)
Sound Wave Parameters
- Frequency (f): measures the occurrence rate of an event, in sound, it refers to the number of complete cycles of pressure variation in one second
- Other key parameters to consider in sound waves include period, wavelength, propagation speed, amplitude, power, and intensity
Attenuation
- Factors influencing attenuation: path length, frequency
- Attenuation coefficient (dB/cm) = half the frequency (MHz), with an average loss of 0.5 dB/cm per MHz frequency
- Equation: Total attenuation (dB) = Attenuation Coefficient (dB/cm) x Path length (cm)
- Factors contributing to attenuation: absorption, reflection, scattering
Acoustic Impedance
- Acoustic impedance (Z) quantifies tissue stiffness and elasticity, determined by the product of tissue density (ρ) and the speed of sound (C)
- Formula: Z = ρ x C, units for Z are expressed in rayls (1 rayl = 1 kg/(m²·s))
- Acoustic impedance disparities influence the transmission and reflection of ultrasound at tissue interfaces
Factors Contributing to Attenuation
Scattering
- Scattering refers to the spread of sound waves in different directions when encountering tissues with irregular surfaces or interfaces similar in size to the wavelength of the sound
- Leads to the reflection of ultrasound waves back to the transducer, known as backscatter
- 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
- Occurs due to the difference in propagation speeds of sound in different media, as defined by Snell's Law
- The direction of the refracted beam depends on the speed of sound in the second medium relative to the first medium
This quiz covers the basics of wave classification, including mechanical waves, electromagnetic waves, longitudinal waves, and transverse waves, with examples and definitions.
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