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Fundamentals of Sonographic Wave Propagation and New Technologies
Michael J. Hartman, MS, RDMS, RVT, RT(R)
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Presentation Disclaimer
The Society of Diagnostic Medical Sonography (SDMS) and the presenter do not endorse the products or companies included in this presentation, nor does the presenter or the SDMS make any assurances of the accuracy of statements or quality of goods and services. The SDMS and presenter have not received any financial compensation from the companies represented in this presentation.
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Objectives Fundamentals of sonographic wave propagation
Classification of sound Classification of waves Propagation velocities Transducers Attenuation New technologies regarding wave propagation
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Sonographic Images How are images formed?
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Transducers Converts energy from one form to another
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Ultrasound Transducer Function
Converts one form of energy to another Electrical to mechanical Mechanical to electrical Pulse-Echo Principle
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How Sonographic Images are Formed
Transducer supplied with electric pulse Transducer converts electrical energy into mechanical energy Sound energy encounters an acoustical interface and is reflected back Transducer converts mechanical energy into electrical energy Internal processor determines the location and strength of the returning signal Reflection is positioned on the display
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SONAR = (SOund Navigation And Ranging)
In use since 1940’s Echo location Determine water depth
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Classification of Sound
Infrasound = < 20 Hz Audible Sound = 20-20,000 Hz Ultrasound = > 20,000 Hz Diagnostic Ultrasound = 2-20 MHz Radiating Waves Non-ionizing “radiation”
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Classification of Waves
Electromagnetic waves Will propagate in a medium or vacuum Mechanical waves Require a medium to propagate
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Propagation of Mechanical Waves
Transverse waves Longitudinal waves
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Longitudinal Wave
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Wavelength Wavelength = the distance a wave travels in a single cycle
Measured in units of distance
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Frequency The number of times a wave is repeated per second
Determined by the source of the wave (transducer) Measured in Hz (or MHz) Higher frequency = Shorter wavelengths Increased resolution Less penetration Lower frequency = Longer wavelengths Decreased resolution Greater penetration
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Frequency One cycle per second = 1 Hertz (Hz)
One thousand Hertz = 1 kilohertz (kHz) One million Hertz = 1 Megahertz (1 MHz) Examples: 3 Hertz = 3 cycles per second 5.0 MHz transducer operates at 5,000,000 cycles per second Image, Courtesy of Pegasus Lectures, Inc.
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Frequency Same propagation speeds, but different frequencies
Wavelength is dependent upon frequency Images, Courtesy of Pegasus Lectures, Inc.
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Period Represents the time it takes between single cycles
Measured in units of time
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Propagation Velocity (Speed of Sound in a Medium)
Wave speed = wavelength × frequency v = λ ƒ (where v is in m/s, λ is in m, and f is in Hz).
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Acoustic Impedance Propagation Velocity (Speed of Sound in a Medium)
Determined by the properties of the medium Density Propagation velocity
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Propagation Velocities
Average speed in soft tissue = 1540 meters/second Image, Courtesy of Pegasus Lectures, Inc.
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Amplitude Amplitude = peak pressure of the wave, intensity of the returning echo
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Amplitude With audible sound:
The loudness of the sound depends on the amplitude of the vibrations The pitch of the sound corresponds to the frequency of the vibrations
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Intensity Intensity = Power Beam area
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Ultrasound Transducer Components
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Elements
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Matching Layer
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Backing Material
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Continuous vs. Pulsed Wave
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Attenuation in Tissue The reduction in power and intensity as sound travels through a medium To diminish or decrease Absorption, reflection, scattering, refraction & diffraction
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Absorption Most dominant attenuation factor in soft tissue
Higher frequencies are absorbed faster than lower frequencies
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Time Gain Compensation (TGC)
Operator-controlled adjustment to compensate for attenuation
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Reflection Image, Courtesy of Pegasus Lectures, Inc.
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Specular Reflector Occurs at large, smooth interfaces
Image, Courtesy of Pegasus Lectures, Inc.
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Scattering Image, Courtesy of Pegasus Lectures, Inc.
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Rayleigh Scattering Image, Courtesy of Pegasus Lectures, Inc.
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Refraction
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Diffraction
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Potential Bioeffects Thermal = generation of heat
Mechanical = production of bubbles (Cavitation )
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Ultrasonic Cleaning Ultrasonic cavitation used for cleaning small items
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Ultrasonic Disintegration
Ultrasonic cavitation used to kill bacteria
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Therapeutic Ultrasound
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Ultrasonic Cavitation/Lipo Cavitation
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Ultrasonic Drug Delivery/ Phonophoresis
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Extracorporeal Shock Wave Lithotripsy (ESWL)
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Percutaneous Nephrolithotomy
Left kidney
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High Intensity Focused Ultrasound (HIFU)
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Focused Ultrasound Guided by MRI
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Silicone Tissue Mimicking Phantom
Before After
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Testing for Initial Accuracy with MR
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Wireless Future of Medicine
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Holter Monitor
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First Wireless Ultrasound System
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Battery and Transducer
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References Kremkau, F. W. (2005). Diagnostic Ultrasound: Principles and Instruments. Philadelphia, PA: Saunders. Miele, F. (2006). Ultrasound Physics & Instrumentation. Forney, Texas: Pegasus Lectures, Inc. Pistol Shrimp Video (2007). Available from Schroeder, A., Kost, J., & Barenholz, Y. (2009). Ultrasound, liposomes, and drug delivery: principles for using ultrasound to control the release of drugs from liposomes. Chemistry and Physics of Lipids, 162(1), 1-16. Siemens (2012). Siemens Acuson Freestyle Wireless Ultrasound Transducer. Available from TedTalks (2011). Yoav Medan: Ultrasound Surgery - Healing Without Cuts. Available from TedTalks (2010). Eric Topol: The Wireless Future of Medicine. Available from Zagzebski, J. A. (1996). Essentials of Ultrasound Physics. St. Louis, Missouri: Mosby.
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