Human Hearing and Ultrasound Frequencies
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Questions and Answers

What does the reflection coefficient (R) measure in terms of sound intensity?

  • The difference in sound speed between two media
  • The ratio of reflected sound intensity to incoming sound intensity (correct)
  • The change in direction of sound waves at an interface
  • The sum of acoustic impedances of two media

    • Which condition contributes to weak reflections in soft tissues during ultrasound imaging?

  • Use of connecting medium with high impedance
  • High acoustic impedance differences
  • Similar acoustic impedances across interfaces (correct)
  • Perpendicular incidence of sound waves

    • What is ultrasonic shadowing primarily caused by?

  • Significant reflection at soft tissue/bone interfaces (correct)
  • Reflection from air interfaces
  • Beam bending at soft tissue interfaces
  • Weak echoes from soft tissues

    • What facilitates the entry of ultrasound into body tissues during an examination?

    <p>Using a connecting medium with similar acoustic impedance</p> Signup and view all the answers

    How does Snell's Law relate to the behavior of sound waves at interfaces?

    <p>It describes the ratio of angles of incidence and refraction based on sound speeds.</p> Signup and view all the answers

    What impact does a larger ultrasound frequency have on pulse length?

    <p>Pulse length is shorter.</p> Signup and view all the answers

    How does lower ultrasound frequency affect resolution?

    <p>It lowers the resolution.</p> Signup and view all the answers

    What is beam bending in the context of ultrasound?

    <p>Sound waves changing direction at an interface</p> Signup and view all the answers

    What zone do tissues need to be located in for good lateral resolution?

    <p>Near field zone</p> Signup and view all the answers

    What is the effect of using acoustic lenses in ultrasound diagnostics?

    <p>They help focus sound waves to enhance imaging.</p> Signup and view all the answers

    What causes the Doppler effect in ultrasound diagnostics?

    <p>Relative motion between the source and the observer.</p> Signup and view all the answers

    Which statement accurately describes the effect of acoustic impedance on ultrasound imaging?

    <p>Significant differences in impedance lead to strong reflections.</p> Signup and view all the answers

    Which of the following best describes the relationship between observed frequency (f’) and emitted frequency (f) when the observer is moving?

    <p>Observed frequency increases with observer speed.</p> Signup and view all the answers

    What happens to the lateral resolution as the ultrasound beam diverges in the far field?

    <p>Lateral resolution deteriorates.</p> Signup and view all the answers

    How is the Doppler-shift (fD) defined?

    <p>The difference between observed and emitted frequencies.</p> Signup and view all the answers

    What is a significant limitation of using higher frequency ultrasound?

    <p>It is more attenuated in tissues.</p> Signup and view all the answers

    What is the range of audible sounds for human hearing?

    <p>20 Hz to 20 kHz</p> Signup and view all the answers

    Which frequency range is typically used in diagnostic sonography?

    <p>2-10 MHz</p> Signup and view all the answers

    What is the speed of sound in soft tissues approximated to?

    <p>1540 m/s</p> Signup and view all the answers

    What happens to the frequency of a sound wave when it travels from one medium to another?

    <p>It remains constant</p> Signup and view all the answers

    What are sound waves with frequencies above 20 kHz called?

    <p>Ultrasounds</p> Signup and view all the answers

    Compressibility is defined as a measure of what?

    <p>Ease of compressing or deforming a medium</p> Signup and view all the answers

    What is the consequence of sound wave propagation concerning wavelength in soft tissues?

    <p>Wavelength is in the range of 0.77-0.154 mm</p> Signup and view all the answers

    What is electrical impedance related to?

    <p>Opposition to current when voltage is applied</p> Signup and view all the answers

    What is the primary function of the damping unit in a transducer?

    <p>To absorb reverse vibrations and produce short pulses</p> Signup and view all the answers

    How does Time Gain Compensation (TGC) affect ultrasound imaging?

    <p>It amplifies signals from deeper tissues to compensate for intensity loss.</p> Signup and view all the answers

    What is the ideal thickness of the piezoelectric plate in a transducer?

    <p>One half of the wavelength of the generated US pulse</p> Signup and view all the answers

    What does the couplant layer in a transducer do?

    <p>Facilitates the transmission of US pulses into the body</p> Signup and view all the answers

    Which statement accurately describes acoustic impedance in the context of a couplant layer?

    <p>It should be equal to the geometric mean of the impedances of the piezoelectric crystal and body tissues.</p> Signup and view all the answers

    What role do transducers play in ultrasound technology?

    <p>They convert between electric energy and mechanical energy.</p> Signup and view all the answers

    What principle explains the phase relationship of sound waves through the couplant layer?

    <p>Constructive interference with matched thickness</p> Signup and view all the answers

    What is the expected behavior of echo signals as they travel to deeper tissues?

    <p>They diminish in intensity due to tissue absorption.</p> Signup and view all the answers

    What is the formula for the Doppler-shift when the US beam is parallel with the direction of blood flow?

    <p>fD = (2v/c)f</p> Signup and view all the answers

    What happens to the Doppler-shift if the US beam is perpendicular to the direction of blood flow?

    <p>The Doppler-shift remains zero</p> Signup and view all the answers

    What represents blood flow toward the transducer in Colour-Doppler imaging?

    <p>Red colors</p> Signup and view all the answers

    Which factor contributes to the weak Doppler-shift observed during blood flow measurement?

    <p>Blood cells deviating slightly from 90°</p> Signup and view all the answers

    What effect does ultrasound have on the medium it propagates through?

    <p>It exerts sound pressure on objects in its direction of propagation</p> Signup and view all the answers

    How does the speed of different particles in a medium affect sound propagation?

    <p>It generates differences in speed among the particles</p> Signup and view all the answers

    What frequency range can the Doppler-shift typically be found in for monitoring purposes?

    <p>20 Hz – 20 kHz</p> Signup and view all the answers

    Which effect is NOT a consequence of high frequency and large amplitude vibrations in sound propagation?

    <p>Temperature rise</p> Signup and view all the answers

    Which scanning method changes the angle of the transducer to adapt to limited transmission of ultrasound pulses?

    <p>Sector scanning</p> Signup and view all the answers

    Imaging artifacts only arise from structural anomalies in the body.

    <p>False</p> Signup and view all the answers

    What is the limit of axial resolution in ultrasound imaging?

    <p>0.5 mm</p> Signup and view all the answers

    The advantage of introducing the transducer into body cavities is that it is close to the organs, reducing the absorption of ultrasound signals. This technique is commonly used in the _____ and _____.

    <p>oesophagus, rectum</p> Signup and view all the answers

    What occurs when ultrasound signals reflect off a strongly reflecting surface, leading to an apparent duplication of the image?

    <p>Mirror-image artifact</p> Signup and view all the answers

    Match the following scanning techniques with their characteristics:

    <p>Linear scanning = Transducer moves in one line Sector scanning = Angle of transducer changes 3D imaging = Combination of multiple 2D images Cavity scanning = Transducer introduced into cavities</p> Signup and view all the answers

    Higher frequencies in ultrasound imaging lead to longer pulse lengths.

    <p>False</p> Signup and view all the answers

    Name one imaging artifact that produces a shadow behind a structure, typically seen in ultrasound imaging.

    <p>Shadowing artifact</p> Signup and view all the answers

    What determines the lateral resolution in ultrasound imaging?

    <p>Beam width (D)</p> Signup and view all the answers

    Higher ultrasound frequency results in greater attenuation in tissues.

    <p>True</p> Signup and view all the answers

    In what part of the ultrasound beam does good lateral resolution occur?

    <p>Near field</p> Signup and view all the answers

    The difference between the observed frequency and emitted frequency is called the ______.

    <p>Doppler-shift (fD)</p> Signup and view all the answers

    Match the following terms with their definitions:

    <p>Near field = Region where lateral resolution is high Far field = Region where beam diverges and resolution decreases Doppler effect = Change in frequency due to relative motion Pulse length = Determined by frequency</p> Signup and view all the answers

    What happens to the near field as the beam width decreases?

    <p>It decreases</p> Signup and view all the answers

    The Doppler effect can only be observed in electromagnetic waves.

    <p>False</p> Signup and view all the answers

    What phenomenon is utilized in ultrasound diagnostics to measure blood flow rate?

    <p>Doppler phenomenon</p> Signup and view all the answers

    What occurs when the pressure in a liquid decreases below its resting level as a result of high-intensity ultrasound?

    <p>Formation of bubbles</p> Signup and view all the answers

    Cavitation bubbles are formed only when liquid is heated to high temperatures.

    <p>False</p> Signup and view all the answers

    What is the primary medical application of High Intensity Focused Ultrasound (HIFU)?

    <p>Eradicating tumours</p> Signup and view all the answers

    The process of breaking kidney stones with focused shock waves is known as __________.

    <p>Extracorporeal Shockwave Lithotripsy (ESWL)</p> Signup and view all the answers

    Match the type of ultrasound effect with its description:

    <p>Micro massage = Mechanical rubbing effect due to particle movement Cavitation = Formation and collapse of small bubbles Hyperthermia = Local temperature increase caused by ultrasound Dispergation = Separation of solid materials using ultrasound</p> Signup and view all the answers

    What are the typical sizes of cavitation bubbles formed during high-intensity ultrasound?

    <p>100 µm</p> Signup and view all the answers

    Higher intensity ultrasound always leads to a reduction in mechanical effects in the medium.

    <p>False</p> Signup and view all the answers

    What are the two primary effects of ultrasound that can lead to significant biological outcomes?

    <p>Thermal and mechanical effects</p> Signup and view all the answers

    What is the range of pulse repetition time (PRT) that can be changed for detecting echo signals?

    <p>100 μs - 1 ms</p> Signup and view all the answers

    Shorter pulse repetition time enhances the ability to detect deeper tissues.

    <p>False</p> Signup and view all the answers

    What is the formula to determine the distance (d) of the echoing surface from the transducer?

    <p>d = ct/2</p> Signup and view all the answers

    In B-mode imaging, the ________ of the echo signal is visualized by the brightness of the pixel on the screen.

    <p>intensity</p> Signup and view all the answers

    Match the imaging modes with their descriptions:

    <p>A-mode = Displays the amplitude of echoes over a single line B-mode = Visualizes the intensity of echoes as brightness M-mode = Shows the movement of reflecting surfaces over time 2D B-mode = Creates cross-sectional images of tissues</p> Signup and view all the answers

    Which statement accurately describes the A-mode ultrasound imaging?

    <p>It detects reflecting surfaces in one line.</p> Signup and view all the answers

    The speed of sound in soft tissues is approximately 1540 m/s.

    <p>True</p> Signup and view all the answers

    What is the primary purpose of using M-mode images in ultrasound diagnostics?

    <p>To visualize the movement of reflecting surfaces like heart valves.</p> Signup and view all the answers

    What formula represents the Doppler-shift when the ultrasound beam is parallel to the direction of blood flow?

    <p>fD = (2v/c)f</p> Signup and view all the answers

    Cosine of 90 degrees impacts the Doppler-shift by reducing it to zero.

    <p>True</p> Signup and view all the answers

    What color represents blood flow towards the transducer in Colour-Doppler imaging?

    <p>Red</p> Signup and view all the answers

    The audible frequency range lies between _____ and _____ Hz.

    <p>20, 20000</p> Signup and view all the answers

    Match the following terms with their respective descriptions:

    <p>Sound Pressure = Pressure exerted by ultrasound on moving objects Doppler-shift = Change in frequency due to motion of source or observer Absorption = Loss of ultrasound energy in the medium Cavitation = Formation of gas bubbles in a liquid due to ultrasound</p> Signup and view all the answers

    What effect describes the behavior of blood cells as secondary sound sources when the echo is formed?

    <p>Doppler shift</p> Signup and view all the answers

    The speed of sound in different particles in a medium always remains the same during propagation.

    <p>False</p> Signup and view all the answers

    What is the primary function of Colour-Doppler technique?

    <p>To visualize and measure blood flow direction and rate</p> Signup and view all the answers

    Study Notes

    Human Hearing Range

    • Humans can hear sounds between 20 Hz and 20 kHz.
    • Higher frequencies are called ultrasounds (US).
    • Lower frequencies are called infrasounds.
    • The upper limit of the US range is a few hundred MHz.
    • Frequencies above this are called hipersounds.

    Diagnostic and Therapeutic US Frequencies

    • Diagnostic sonography typically uses 2–10 MHz US.
    • Therapeutic applications use lower frequencies but with much larger US intensities.

    Speed of Sound

    • The speed of sound (c) in a medium is determined by density (ρ) and compressibility ().
    • Compressibility measures how easily a medium compresses or deforms.
    • Solids have higher densities but lower compressibilities than gases, resulting in faster sound speeds (~3000-6000 m/s).
    • The speed of sound in soft tissues is approximately 1540 m/s.

    Frequency and Wavelength

    • Frequency does not change when a sound wave travels between mediums.
    • The wavelengths of 2-10 MHz US in soft tissues are in the range of 0.77-0.154 mm.

    Acoustic Impedance

    • Acoustic impedance is the opposition a circuit presents to a current when a voltage is applied.
    • Reflection of sound waves is determined by the difference in acoustic impedance between two mediums, resulting in the reflection coefficient (R).
    • Soft tissues have similar acoustic impedances, resulting in weak reflections (echoes).
    • The difference in acoustic impedance between soft tissue and bone is large, resulting in strong echoes from bone surfaces and ultrasonic shadowing.
    • Air and soft tissue have very different acoustic impedances, requiring a coupling medium like gel or water for sound transmission.

    Refraction

    • Sound wave direction can change when entering a different medium, known as refraction.
    • The amount of refraction is determined by Snell's Law and depends on the change in sound speed between the mediums.
    • Refraction can contribute to image artefacts in US diagnostics and can be used for focusing sound waves with acoustic lenses.

    Pulse-Echo Method

    • The same transducer is used for generating and detecting US pulses.
    • Higher frequency US pulses are shorter, leading to higher resolution.
    • Lower frequency US pulses are longer, lowering resolution, but are less attenuated in tissues.

    Lateral Resolution

    • Lateral resolution is determined by the beam width (D).
    • The US beam has a near field (Fresnel zone) and a far field (Fraunhofer zone).
    • The near field provides good lateral resolution, while the far field diverges, leading to poorer resolution.
    • The optimal bean width ensures that the structures of interest are in the near field with good lateral resolution.

    Doppler Effect

    • The Doppler effect occurs when a source and observer are in relative motion.
    • The observed frequency differs from the emitted frequency.
    • US can be used to measure blood flow rate by detecting frequency shifts in the US signal scattered by blood cells.

    US Imaging Techniques

    • Colour-Doppler imaging displays blood flow direction as red (towards the transducer) and blue (away from the transducer) superimposed on 2D B-mode images.

    US Effects

    • The high frequency and large amplitude vibrations of US can exert pressure, absorb energy, cause cavitation, and produce mechanical rubbing effects on the medium.

    US Intensity

    • Sound pressure is directly proportional to US intensity.

    Transducer Components

    • Transducers are devices that convert one type of energy to another (electric energy↔mechanical energy).
    • The actual sound-generating and detecting component is a thin piezoelectric plate or crystal.
    • A damping unit made from a high absorption coefficient material is used to reduce vibrations in the reverse direction and produce short US pulses.
    • The couplant layer protects the piezoelectric plate and facilitates US transmission into the body.

    Couplant Layer

    • The ideal thickness of the couplant layer is one-fourth of the emitted US wavelength.
    • The acoustic impedance of the couplant layer should be equal to the geometric mean of the piezoelectric crystal and the body tissues.

    Practical US Applications

    • US can be used in diagnostic imaging and therapeutic applications.
    • It can also be used to measure blood flow rates.

    Ultrasound Basics

    • Ultrasound pulses are very short, lasting only a few microseconds.
    • The time between pulses (PRT) is adjustable, with longer PRT allowing detection of echoes from deeper tissues.
    • The speed of sound in tissue is approximately 1540 m/s.
    • We can determine the distance to a reflecting surface using the arrival time of the echo and the speed of sound.

    Ultrasound Imaging Modes

    • A-mode: One-dimensional imaging, displaying echo signal intensity against arrival time.
    • B-mode: One-dimensional image where intensity is represented by brightness, forming the basis of more complex imaging modes.
    • M-mode: Creates a series of B-mode images over time, visualizing movement of reflecting surfaces like heart valves.
    • 2D B-mode: Generates cross-sectional images by combining multiple one-dimensional B-mode images.
    • Linear scanning involves moving the transducer in a straight line.
    • Sector scanning changes the angle of the transducer, beneficial for imaging through limited spaces like between ribs.
    • Transducers can be inserted into body cavities for closer examination and reduced signal attenuation.
    • 3D images can be created from multiple 2D images taken at different angles.

    Ultrasound Artefacts

    • Shadows: Areas of decreased echo signal intensity behind strongly reflecting structures like kidney stones.
    • Mirror Images: Duplication of an object's image due to reflections from a strongly reflecting surface.

    Spatial Resolution

    • Axial Resolution: Ability to distinguish between two structures lying along the axis of the ultrasound beam.
      • Improved by higher frequencies, leading to shorter pulses.
      • Limited by pulse length, typically 2-3 cycles in modern scanners.
    • Lateral Resolution: Ability to distinguish between two structures lying perpendicular to the axis of the ultrasound beam.
      • Determined by the width of the ultrasound beam.
      • Best in the near field (Fresnel zone), deteriorates in the far field (Fraunhofer zone).

    Doppler Effect

    • The observed frequency of a wave changes when there is relative motion between the source and the observer.
    • Used in ultrasound to measure blood flow rate.
    • Red blood cells scatter ultrasound waves, and the change in frequency (Doppler shift) is proportional to the speed of the blood flow.
    • Doppler shift typically lies in the audiofrequency range (20 Hz - 20 kHz), allowing the operator to hear the signal.

    Primary Effects of Ultrasound

    • Sound Pressure: The force exerted by ultrasound waves, directly proportional to intensity.
    • Absorption: Ultrasound energy is absorbed by tissues, generating heat.
    • Cavitation: Formation and collapse of bubbles in a liquid due to pressure changes caused by ultrasound.
    • Mechanical Rubbing Effect: Friction between particles of different sizes in a medium caused by ultrasound.

    Secondary Effects of Ultrasound

    • Dispersion: Spreading of solid materials caused by mechanical rubbing effect.
    • Chemical Reactions: Induced by the heat generated from ultrasound absorption.
    • Biological Effects: Cell damage and other effects caused by thermal and mechanical forces.

    Medical Applications of Ultrasound

    • HIFU (High Intensity Focused Ultrasound): Uses focused ultrasound to generate heat and cavitation, destroying tumors.
    • ESWL (Extracorporeal Shockwave Lithotripsy): Breaks kidney stones using high-intensity shock waves.

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    Physical Properties of Sound, Ultrasound, Debrecen University 2019

    Description

    Explore the fascinating world of human hearing and ultrasound frequencies. This quiz covers the range of sounds humans can hear, the characteristics of infrasound and ultrasound, and the physics behind the speed of sound in various mediums. Test your knowledge on diagnostic and therapeutic ultrasound applications.

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