Fundamentals of Sonographic Wave Propagation and New Technologies

Fundamentals of Sonographic Wave Propagation and New Technologies

Fundamentals of Sonographic Wave Propagation and New Technologies Michael J. Hartman, MS, RDMS, RVT, RT(R) 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. Objectives

Fundamentals of sonographic wave propagation Classification of sound Classification of waves Propagation velocities

Transducers Attenuation New technologies regarding wave propagation Sonographic Images

How are images formed? Transducer s Converts energy from one form to another

Ultrasound Transducer Function Converts one form of energy to another Electrical to mechanical Mechanical to electrical Pulse-Echo Principle

How Sonographic Images are Formed 1. 2. 3.

4. 5. 6.

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 SONAR = (SOund Navigation And Ranging) In use since 1940s Echo location

Determine water depth 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 Classification of Waves Electromagnetic waves

Will propagate in a medium or vacuum Mechanical waves

Require a medium to propagate Propagation of Mechanical Waves Transverse

waves Longitudinal waves

Longitudinal Wave Wavelength Wavelength = the distance a wave travels

in a single cycle Measured in units of distance 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

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. Frequency

Same propagation speeds, but different frequencies Wavelength is dependent upon frequency

Images, Courtesy of Pegasus Lectures, Inc. Period Represents the time it takes between single cycles Measured in units of time

Propagation Velocity (Speed of Sound in a Medium) Wave speed = wavelength frequency v=

(where v is in m/s, is in m, and f is in Hz). Acoustic Impedance Propagation Velocity (Speed of Sound in a Medium) Determined by the properties of the medium Density

Propagation velocity Propagation Velocities Average speed in soft tissue = 1540 meters/second Image, Courtesy of Pegasus Lectures, Inc.

Amplitude Amplitude = peak pressure of the wave, intensity of the returning echo

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 Intensity

Intensity = Power Beam area Ultrasound Transducer Components

Elements Matching Layer Backing Material

Continuous vs. Pulsed Wave Attenuation in Tissue The reduction in power and intensity as sound travels through a medium To diminish or decrease

Absorption, reflection, scattering, refraction & diffraction Absorption Most dominant attenuation factor in soft tissue Higher frequencies are absorbed faster than

lower frequencies Time Gain Compensation (TGC) Operator-controlled adjustment to

compensate for attenuation Reflection Image, Courtesy of Pegasus Lectures, Inc.

Specular Reflector Occurs at large, smooth interfaces Image, Courtesy of Pegasus Lectures, Inc. Scattering

Image, Courtesy of Pegasus Lectures, Inc. Rayleigh Scattering Image, Courtesy of Pegasus Lectures, Inc.

Refraction Diffraction Potential Bioeffects

Thermal = generation of heat Mechanical = production of bubbles (Cavitation ) Ultrasonic Cleaning

Ultrasonic cavitation used for cleaning small items Ultrasonic Disintegration Ultrasonic cavitation used to kill bacteria Therapeutic Ultrasound

Ultrasonic Cavitation/Lipo Cavitation Ultrasonic Drug Delivery/ Phonophoresis

Extracorporeal Shock Wave Lithotripsy (ESWL) Percutaneous Nephrolithotomy

Left kidney High Intensity Focused Ultrasound (HIFU) Focused Ultrasound Guided

by MRI Silicone Tissue Mimicking Phantom Before

After Testing for Initial Accuracy with MR

Wireless Future of Medicine Holter Monitor First Wireless Ultrasound System

Battery and Transducer 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

http://www.youtube.com/watch?v=eKPrGxB1Kzc&feature=player_embedded 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 http://www.youtube.com/watch?v=DfNe_EAMcAw TedTalks (2011). Yoav Medan: Ultrasound Surgery - Healing Without Cuts. Available from http://www.youtube.com/watch?v=x4lA-M3zbdU TedTalks (2010). Eric Topol: The Wireless Future of Medicine. Available from

http://www.ted.com/talks/eric_topol_the_wireless_future_of_medicine.html Zagzebski, J. A. (1996). Essentials of Ultrasound Physics. St. Louis, Missouri: Mosby.

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