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?

Transducers 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 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 1940’s 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 = λ ƒ (where v is in m/s, λ 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.