Glossary

uses sound waves to create images and measure motion inside the body. It's based on how these waves interact with different tissues, bouncing back to create detailed pictures. This non-invasive technique is crucial in medical diagnostics and treatments.

, the , and the effect are key concepts in ultrasound. Understanding these principles helps us interpret ultrasound images and measure things like blood flow, making it a versatile tool in healthcare and industry.

Ultrasound Fundamentals

Acoustic impedance in ultrasound

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  • Acoustic impedance (ZZ) measures resistance to sound wave propagation in a material
    • Calculated as the product of density (ρ\rho) and sound speed (vv): Z=ρvZ = \rho v
    • Materials with high acoustic impedance (bone) reflect more sound energy
    • Low acoustic impedance materials (air) allow more sound transmission
  • Impedance mismatches at interfaces cause reflections crucial for ultrasound imaging
    • Larger mismatches produce stronger reflections (soft tissue-bone interface)
  • Intermediate impedance matching layers minimize reflections and improve energy transfer (-skin interface)

Medical and industrial ultrasound applications

  • Medical applications:
    • Diagnostic imaging visualizes internal body structures
      • Obstetrics monitors fetal development (gestational age, congenital abnormalities)
      • Cardiology assesses heart function and blood flow (valve disorders, cardiac output)
      • Musculoskeletal evaluates muscles, tendons, and ligaments (tears, inflammation)
    • Therapeutic uses:
      • Physiotherapy promotes tissue healing and reduces pain (tendinitis, muscle strains)
      • (HIFU) treats tumors and abnormalities (prostate cancer, uterine fibroids)
  • Industrial applications:
    • (NDT) inspects materials for defects without damage
      • Flaw detection in welds, castings, and composites (cracks, voids, inclusions)
      • Thickness measurements and corrosion monitoring (pipelines, storage tanks)
    • Ultrasonic cleaning removes contaminants from surfaces with high- vibrations (jewelry, surgical instruments)
    • Ultrasonic welding joins plastics and metals using high-frequency vibrations (automotive components, packaging)
    • Flow metering measures fluid flow rates in pipes and channels (water, oil, gas)

Ultrasound wave properties and interactions

  • Frequency: Number of wave cycles per second, measured in (Hz)
  • : Distance between consecutive wave peaks, inversely related to frequency
  • : Sound waves bounce off interfaces between materials with different acoustic impedances
  • : Change in wave direction when passing between materials with different sound speeds
  • : Dispersion of sound waves in multiple directions due to small irregularities or particles
  • : Amount of energy transported by the wave per unit area per unit time

Pulse-echo technique

  • Fundamental method used in ultrasound imaging and non-destructive testing
  • Transducer emits short pulses of ultrasound waves into the medium
  • Waves reflect off interfaces and return to the transducer
  • Time delay between pulse emission and echo reception determines distance to reflecting interface
  • Amplitude of received echo indicates acoustic impedance mismatch at interface

Ultrasound Calculations and Applications

Calculation of acoustic impedance

  • Acoustic impedance (ZZ) is the product of density (ρ\rho) and sound speed (vv): Z=ρvZ = \rho v
    • Density is mass per unit volume (kg/m³)
    • Sound speed depends on material stiffness and compressibility
  • Example: Calculate acoustic impedance of water with density 1000 kg/m³ and sound speed 1480 m/s
    • Z=ρv=(1000 kg/m³)(1480 m/s)=1.48×106 kg/(m²\cdotps)Z = \rho v = (1000 \text{ kg/m³})(1480 \text{ m/s}) = 1.48 \times 10^6 \text{ kg/(m²·s)}

Doppler effect for velocity measurement

  • Doppler effect is the frequency change observed when source or receiver moves relative to medium
    • Frequency increases when source and receiver approach each other
    • Frequency decreases when source and receiver move apart
  • In ultrasound, Doppler effect measures velocity of moving objects (blood cells)
  • Doppler shift (Δf\Delta f) is the difference between received (frf_r) and transmitted (ftf_t) frequencies: Δf=fr−ft\Delta f = f_r - f_t
  • Object velocity (vv) is calculated using Doppler shift equation: v=cΔf2ftcos⁡θv = \frac{c \Delta f}{2 f_t \cos \theta}
    • cc is sound speed in medium
    • θ\theta is angle between ultrasound beam and object motion direction
  • Example: Calculate blood cell velocity with transmitted frequency 5 MHz, received frequency 5.1 MHz, sound speed in tissue 1540 m/s, and angle between ultrasound beam and blood flow 45°
    1. Calculate Doppler shift: Δf=fr−ft=5.1 MHz−5 MHz=0.1 MHz=100 kHz\Delta f = f_r - f_t = 5.1 \text{ MHz} - 5 \text{ MHz} = 0.1 \text{ MHz} = 100 \text{ kHz}
    2. Calculate velocity: v=cΔf2ftcos⁡θ=(1540 m/s)(100×103 Hz)2(5×106 Hz)(cos⁡45°)≈0.22 m/sv = \frac{c \Delta f}{2 f_t \cos \theta} = \frac{(1540 \text{ m/s})(100 \times 10^3 \text{ Hz})}{2(5 \times 10^6 \text{ Hz})(\cos 45°)} \approx 0.22 \text{ m/s}

Key Terms to Review (27)

A-mode: A-mode, or Amplitude mode, is a type of ultrasound imaging technique that displays the amplitude of the reflected ultrasound waves as a function of time. This mode is primarily used to provide information about the depth and intensity of structures within the body.
Acoustic Impedance: Acoustic impedance is a measure of the opposition that a surface presents to the flow of acoustic energy. It is the ratio of the sound pressure to the particle velocity at a given point in a medium, and it determines how much sound energy is reflected or transmitted at the boundary between two media.
Attenuation Coefficient: The attenuation coefficient is a measure of how quickly the intensity of a wave, such as ultrasound, diminishes as it propagates through a medium. It quantifies the amount of energy lost as the wave travels through a material.
B-mode: B-mode, or Brightness mode, is an imaging technique used in ultrasound that displays the intensity of reflected sound waves as a two-dimensional image. It is one of the primary modes of operation in diagnostic ultrasound, providing a visual representation of the internal structures of the body.
Beat frequency: Beat frequency is the frequency at which two waves of slightly different frequencies interfere with each other, resulting in a modulation pattern perceived as a periodic variation in amplitude. It is calculated as the absolute difference between the frequencies of the two interfering waves.
Cavitation: Cavitation is the formation and subsequent collapse of small bubbles or cavities within a liquid, typically in areas of low pressure. This phenomenon is particularly relevant in the context of ultrasound, where it can have significant implications.
De Broglie wavelength: The de Broglie wavelength is the wavelength associated with a particle and is inversely proportional to its momentum. It highlights the wave-particle duality of matter.
Decibel: The decibel (dB) is a logarithmic unit used to measure the intensity or level of various quantities, including sound, electricity, and radio signals. It is a relative measure that compares the magnitude of a quantity to a reference value, often the threshold of human hearing or a standard power level.
Doppler: The Doppler effect is the change in the observed frequency or wavelength of a wave due to the relative motion between the source and the observer. This phenomenon is widely used in various fields, including ultrasound imaging, to detect and measure the motion of objects or fluids.
Doppler-shifted ultrasound: Doppler-shifted ultrasound is a technique used to measure the change in frequency of sound waves due to the motion of an object, such as blood flow in vessels. It utilizes the Doppler effect to provide information about the speed and direction of moving objects.
Frequency: Frequency is a fundamental concept in physics that describes the number of occurrences of a repeating event per unit of time. It is a crucial parameter in various areas of study, including radiation, oscillations, waves, sound, and electromagnetic phenomena.
Hertz: Hertz is the unit of frequency, defined as one cycle per second. It is crucial in understanding oscillatory motion, where it quantifies how often an event occurs within a given time frame. This term is also important in various contexts, such as sound waves and electromagnetic waves, where frequency affects their properties and behaviors.
High-Intensity Focused Ultrasound: High-Intensity Focused Ultrasound (HIFU) is a non-invasive therapeutic technique that uses focused ultrasound waves to target and ablate specific tissues within the body. This technology allows for the precise delivery of thermal energy to a localized area, making it a valuable tool in various medical applications.
Intensity: Intensity is the power per unit area carried by a wave, typically measured in watts per square meter ($W/m^2$). It quantifies the energy flow through a given surface area perpendicular to the direction of wave propagation.
Intensity: Intensity is a measure of the amount of energy or power transmitted through a given area per unit of time. It is a fundamental concept that describes the strength or magnitude of a physical quantity, such as a wave, field, or radiation, and is crucial in understanding various phenomena in physics.
Intensity reflection coefficient: The intensity reflection coefficient is a measure of the fraction of incident acoustic wave intensity that is reflected at the boundary between two different media. It is a dimensionless quantity and ranges from 0 to 1.
Non-destructive Testing: Non-destructive testing (NDT) refers to a wide range of analysis techniques used to evaluate the properties of a material, component, or system without causing damage. This approach is particularly valuable in the context of ultrasound, as it allows for the assessment of internal structures and defects without compromising the integrity of the tested object.
Piezoelectric Crystal: A piezoelectric crystal is a material that can generate an electric charge in response to mechanical stress or pressure. This property is known as the piezoelectric effect and is the fundamental principle behind many technological applications, including ultrasound imaging.
Piezoelectric Effect: The piezoelectric effect is a property of certain materials, typically crystals and ceramics, that can generate an electric charge in response to mechanical stress or strain. This effect can also work in reverse, where applying an electric field to the material causes it to deform or vibrate.
Pulse-echo technique: The pulse-echo technique is a method used in ultrasound imaging to detect and measure the properties of objects or structures within a medium, such as the human body. It involves transmitting a brief pulse of high-frequency sound waves and then analyzing the echoes that are reflected back from the various interfaces within the medium.
Reflection: Reflection is the change in direction of a wave, such as light or sound, when it encounters a boundary or surface. It is a fundamental concept in physics that describes how waves interact with different media and surfaces, leading to various phenomena observed in the physical world.
Refraction: Refraction is the bending of a wave, such as light or sound, when it passes from one medium to another with a different density or refractive index. This phenomenon occurs due to the change in the speed of the wave as it moves between the two mediums, causing it to change direction.
Scattering: Scattering is the process by which particles or waves deviate from their original path due to interactions with other particles or inhomogeneities in the medium they are traveling through. This phenomenon is particularly relevant in the context of ultrasound, where sound waves interact with various tissues and structures within the body.
Sonography: Sonography, also known as ultrasonography, is a diagnostic imaging technique that uses high-frequency sound waves to create visual images of structures within the body. It is a non-invasive and radiation-free method of obtaining information about the internal organs, tissues, and blood flow.
Transducer: A transducer is a device that converts one form of energy into another, typically by taking a physical input and converting it into an electrical signal. Transducers are essential components in a wide range of applications, including sensors, actuators, and various types of measurement and control systems.
Ultrasound: Ultrasound is a non-invasive imaging technique that uses high-frequency sound waves to create detailed images of the body's internal structures. It is a versatile tool used in various medical applications, from diagnostic procedures to therapeutic interventions.
Wavelength: Wavelength is a fundamental characteristic of waves, representing the distance between consecutive peaks or troughs in a wave. It is a crucial parameter that describes the spatial extent of a wave and is closely related to other wave properties such as frequency and speed.
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