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Questions and Answers
What frequency range is classified as ultrasound?
What frequency range is classified as ultrasound?
What is the main advantage of using ultrasound over X-ray techniques?
What is the main advantage of using ultrasound over X-ray techniques?
How is acoustic impedance (Z) defined?
How is acoustic impedance (Z) defined?
What phenomenon occurs when sound waves hit an interface between two media with different acoustic impedances?
What phenomenon occurs when sound waves hit an interface between two media with different acoustic impedances?
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In what application can infrasonic noise potentially cause psychological effects?
In what application can infrasonic noise potentially cause psychological effects?
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What does the intensity of a sound wave primarily depend on?
What does the intensity of a sound wave primarily depend on?
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What happens when the acoustic impedances of two mediums are equal?
What happens when the acoustic impedances of two mediums are equal?
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How can seismocardiograms be used in the medical field?
How can seismocardiograms be used in the medical field?
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Which medium does sound travel fastest through?
Which medium does sound travel fastest through?
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What is the mathematical representation of frequency related to the period of a sound wave?
What is the mathematical representation of frequency related to the period of a sound wave?
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Which frequency range is classified as infrasound?
Which frequency range is classified as infrasound?
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In the context of ultrasound imaging, what does acoustic impedance depend on?
In the context of ultrasound imaging, what does acoustic impedance depend on?
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What principle does SONAR technology primarily utilize?
What principle does SONAR technology primarily utilize?
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What is primarily produced during the ultrasound imaging process?
What is primarily produced during the ultrasound imaging process?
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Which of the following best describes the term 'wavelength' in sound waves?
Which of the following best describes the term 'wavelength' in sound waves?
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Which of the following does not affect the speed of sound in a medium?
Which of the following does not affect the speed of sound in a medium?
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What effect does acoustic impedance have on ultrasound wave interaction?
What effect does acoustic impedance have on ultrasound wave interaction?
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How can refraction in ultrasound imaging be minimized?
How can refraction in ultrasound imaging be minimized?
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What characterizes the phenomenon of attenuation in ultrasound imaging?
What characterizes the phenomenon of attenuation in ultrasound imaging?
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What primarily determines the quality of ultrasound imaging?
What primarily determines the quality of ultrasound imaging?
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What is the purpose of using a coupling gel in ultrasound procedures?
What is the purpose of using a coupling gel in ultrasound procedures?
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What is the significance of spatial resolution in ultrasound imaging?
What is the significance of spatial resolution in ultrasound imaging?
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Which type of reflection is more likely to cause an intensity loss in the echo signal?
Which type of reflection is more likely to cause an intensity loss in the echo signal?
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What is the effect of using thicker coupling gel in ultrasound imaging?
What is the effect of using thicker coupling gel in ultrasound imaging?
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Study Notes
Sound in Medicine 2024
- Topics covered include characteristics of sound waves, reflection and transmission, intensity levels, applications in medicine, percussion and stethoscopes, sonar, US generation, image quality, US imaging modes, and physiological effects.
General Properties of Sound
- A sound wave is a pattern of disturbance caused by energy traveling away from the source.
- Waves transfer energy without transferring matter.
- Sound is a mechanical disturbance that propagates through an elastic medium at a specific velocity.
- In air, sound is characterized by fluctuations in pressure (compressions and rarefactions) relative to atmospheric pressure.
Sound Velocity
- Sound travels fastest in solids, slower in liquids, and slowest in gases.
- Air: 330 m/sec
- Water: 1480 m/sec
- Muscle: 1580 m/sec
- Bone: 4080 m/sec
Frequency and Wavelength
- Frequency (f) is the number of rarefactions and compressions per unit time.
- Wavelength (λ) is the distance between successive compressions or rarefactions.
- The relationship between frequency, wavelength, and velocity (v) is: v = fλ.
Sonic Spectrum
- The sonic spectrum is classified into infrasound, audible sound, and ultrasound based on frequency.
- Audible range (human hearing): 20 Hz to 20 kHz.
- Infrasound: Below 20 Hz.
- Ultrasound: Above 20 kHz.
Infrasonic Effects on the Human Body
- Infrasound can travel long distances without losing much power.
- Intense infrasound can cause clear symptoms like respiratory impairment, aural pain, fear, visual hallucinations, and chills.
Ultrasound
- Ultrasound has a frequency above 20 kHz.
- Used in medical applications.
- More informative than X-rays; less harmful for the fetus.
- Used in the study of heart mechanical function (seismocardiogram).
- Diagnotics of structures (tissues).
Intensity of a Sound Wave
- Sound intensity is the energy carried per unit area and time.
- Expressed by the maximum change in pressure.
Acoustic Impedance
- Acoustic impedance is a substance's resistance to sound.
- Acoustic impedance (Z)= pv
- Z value affects reflection and transmission of sound.
- Small difference in acoustic impedance results in low reflection and high transmission.
- Large difference in acoustic impedance results in high reflection and low transmission
- Substances with larger Z are more reflective than those with lower Z.
Intensity Level Ratio
- The intensity level (in dB) is a logarithmic scale for comparing sound intensities to a reference.
- Formula for intensity level in decibels (dB) is: Intensity level = 10 log10
( I/ I₀)
- I is the intensity of the sound
- I₀ is a reference intensity ( usually 10⁻¹² W/m²)= hearing threshold)
Effect of Sound on Human Hearing
- Loudness: Intensity of the sound
- Pitch: Frequency of the sound
Sound Reflection and Transmission
- Sound reflects when it encounters a boundary between media with different acoustic impedance.
- The reflection ratio (R) and transmission ratio (T) depend on the acoustic impedance mismatch.
Percussion
- Percussion is a diagnostic technique using sounds produced by striking the body surface.
- Resonant, hyper-resonant, and dull are different types of percussion sounds.
Stethoscopes
- Stethoscopes amplify sounds from the body.
- Consist of a bell and diaphragm within a tubing system.
US Image Production
- Focal zone, acoustic impedance, and refraction impact US image production.
US Imaging Modes
- A-Mode (1D): Measures the depth of interfaces based on echo time.
- B-Mode (2D): A storage oscilloscope displays 2D images of internal structures.
- M-Mode (2D + motion): Stationary transducer displays motion.
- D-Mode (3D + motion/4D): Adds a time dimension capturing 3D images with motion.
Ultrasound Applications
- Ophthalmology: diagnosis of eye diseases, biometry (measurement of eye structures).
- Echo encephalography: detection of brain tumors.
Physiological Effects of Ultrasound in Therapy
- Low intensity ultrasound (0.01 W/cm²): Diagnostic work (e.g. Sonar) no harmful effects.
- Moderate intensity ultrasound (1–10 W/cm²): Heating effects (diathermy), and micromassage
- High intensity ultrasound (35 W/cm²): tissue destruction.
- Focused ultrasound (~10³ W/cm²): Deep tissue destruction.
Quality of Ultrasound Imaging
- Spatial resolution is determined by the wavelength; a shorter wavelength results in better spatial resolution.
- Attenuation is determined by intensity and propagation distance (exponential decrease).
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