Introduction to the Introduction to the Physics Physics

Echocardiography Echocardiography

Jose L. Rivera, M.D.Jose L. Rivera, M.D.January 9, 2010January 9, 2010

The Basic PhysicsThe Basic Physics

• Image Generation: The Physics of Image Generation: The Physics of Ultrasound Doppler Imaging Modalities & Ultrasound Doppler Imaging Modalities & Measurement of Blood VelocitiesMeasurement of Blood Velocities

• Use of Calculus to manipulate ultrasound Use of Calculus to manipulate ultrasound Doppler informationDoppler information

ObjectivesObjectives

• Explain how the various modes of Explain how the various modes of ultrasound image are generatedultrasound image are generated

• Define the basic physics and calculus Define the basic physics and calculus concepts used in medical ultrasound concepts used in medical ultrasound imagingimaging

ObjectivesObjectives

• Discuss the utility and applications of Discuss the utility and applications of Doppler color flows imaging.Doppler color flows imaging.

• Explain the difference between Pulsed Explain the difference between Pulsed Doppler and Continuous Doppler and their Doppler and Continuous Doppler and their applicationsapplications

Physics of EchocardiographyPhysics of Echocardiography

Brief Review of Echocardiography Physics to:

Understand the generation, propagation and detection of Ultrasounds Waves

Explain how the physical principles affect our measurements and images

Appreciate the strengths and limitations of the technology

THE BASIC PHYSICSTHE BASIC PHYSICS

• ULTRASOUND WAVES IN A FLUID BEHAVE ULTRASOUND WAVES IN A FLUID BEHAVE LIKE ELECTROMAGNETIC WAVES IN A LIKE ELECTROMAGNETIC WAVES IN A VACUUMVACUUM

• THEIR ENERGY SOURCE ORIGINATES FROM THEIR ENERGY SOURCE ORIGINATES FROM ELECTROMAGNETIC WAVES & THEY RETAIN ELECTROMAGNETIC WAVES & THEY RETAIN SOME OF THOSE WAVE PROPERTIESSOME OF THOSE WAVE PROPERTIES

• THEIR PROPERTIES CAN BE ANALYZED WITH THEIR PROPERTIES CAN BE ANALYZED WITH BASIC CALCULUS (Integral & Differential)BASIC CALCULUS (Integral & Differential)

• The following diagrams on the following slides were obtained from Sidebotham’s The following diagrams on the following slides were obtained from Sidebotham’s “Perioperative Transesophageal Echocardiography“Perioperative Transesophageal Echocardiography

Piezoelectric EffectPiezoelectric Effect

Piezoelectric effect results inCompression & Rarefaction: The Shockwave

Damping Material is used to “ring down” the Pulse Length & Bandwidth which results in

improved resolution

Ultrasound Interactions with Tissue

Interfaces

Arrow represent Vectors whose length equal the Arrow represent Vectors whose length equal the strength & direction of the reflected signalstrength & direction of the reflected signal

A and B represent specular (mirror like) reflectors, A and B represent specular (mirror like) reflectors, the B return signal does not return to the transducerthe B return signal does not return to the transducer

C and D have a rough surface that is typical of human C and D have a rough surface that is typical of human tissuetissue

E are objects smaller than a wavelength & therefore E are objects smaller than a wavelength & therefore scatter the energyscatter the energy

Interactions of Ultrasound Waves with Interactions of Ultrasound Waves with TissueTissue

The interactions will determine the types of The interactions will determine the types of images & artifacts that are generatedimages & artifacts that are generated

Reflection, Attenuation & Reflection, Attenuation & Time Gain Time Gain Conpensation Conpensation SettingsSettings

Transducer Frequency & Wavelength affect Transducer Frequency & Wavelength affect Resolution & PenetrationResolution & Penetration

TRANSDUCERSTRANSDUCERSDESIGNDESIGN

• Piezoelectric Principle is universal• Linear Array

Nerve Block probe

• Mechanical Sector Scan old Site Rite

• Phase Array Design• 3D probes

Mechanical Sector Scan

PHASE ARRAY TRANSDUCERGenerating the Summation Wave front

Steering the Phase Array Summation Wave Front

3D probes3D probes

Types of Ultrasound “Formats”

• A mode (amplitude)• B mode (brightness) Most common• M mode (motion) • Doppler

Pulse WaveContinuous WaveColor Flow

• 3D

A Mode (amplitude) B Mode (2D) M Mode A Mode (amplitude) B Mode (2D) M Mode (motion)(motion)

3D Format3D Format

• Fig 3.48 video.avi

SUMMARY• Understanding Echocardiography

Physics will enhance our understanding of:

• The physical principles that affect our measurements and images

• Knowing when to believe or doubt our results

• The strengths and limitations of the technology