chapter 1 fact_sheet_-_principles

Physics of Ultrasound

Ultrasound WaveUltrasound WaveNOTE: The higher the frequency the better the resolution!However you lose you loose penetration!

Compression

NOTE: The higher the frequency the better the resolution!However you lose you loose penetration!

Decompression


Velocity of ultrasound is 1540 m/s in tissue and 1570 m/s in blood


Medical UltrasoundMedical Ultrasound

Frequencies between 2- 10 MHz are used!

Ultrasound Wave is generated by Piezoelectric crystals

Receive signal (echo) is used to generate images!

Safety of UltrasoundSafety of UltrasoundSafety of Ultrasound

No known adverse effects of diagnostic ultrasoundNo known adverse effects of diagnostic ultrasound

Thermal effects (depdendant on intensity)

Cavitations

Ultrasound Pulse

The higher the US frequency the higher the pulse repetition frequency

NOTE: The higher the pulse repetition frequency, the higher the frame rate and image resolution!

001 // Principles of Echocardiography

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2D Image

2D Image

NOTE: Ultrasound is a cutplane technique. Multiple elements are used to generate a 2D image!

Types of ProbesTypes of Probes

NOTE: In echocardiography curvilinear probes are used! The advantage is its small footprint, thus it can also be used to image from intercostal spaces! Scan line density is an important factor for image quality!

Image QualityImage QualityImage Quality

Spacial resolution — lateral Contrast resolution

Spacial resolution — axial Temporal resolution


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Determinants of Spacial ResolutionDeterminants of Spacial Resolution

Lateral resolution Axial resolution

Beam width/ line density Frequency

Frequency Pulse frequency

Gain

Harmonic ImagingHarmonic Imaging

NOTE: Harmonic imaging uses the resonance characteristics of tissue! The send and receive frequency of the transducers differ. Advantage: Less artefacts, better image quality

Frame Rate — InfluenceFrame Rate — InfluenceFrame Rate — Influence

Frame Rate = Frames / sec Frame Rate = Frames / sec

Sector width Frequency

Scan lines Depth

NOTE: High frame rates are useful in combination with the image review function! (Detection of rapid motion)NOTE: High frame rates are useful in combination with the image review function! (Detection of rapid motion)NOTE: High frame rates are useful in combination with the image review function! (Detection of rapid motion)

Limitations of 2D ImagingLimitations of 2D Imaging

Attenuation Influence of tissue

Artefacts Penetration


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AttenuationAttenuationAttenuation

Definition: Decrease in amplitude and intensity as an ultrasound wave travels through a mediumDefinition: Decrease in amplitude and intensity as an ultrasound wave travels through a medium

Absorption (proportional to frequency)

Reflection

Refraction Shadowing

Transfer of energy from the beam to the tissue

Pseudoenhancement

Enemies of UltrasoundEnemies of UltrasoundEnemies of Ultrasound

Tissue Bone Air

Penetration Absorption Reflection

NOTE: Imaging is difficult in patient with small intercostal spaces (bone) and in patients with COPD (air)!NOTE: Imaging is difficult in patient with small intercostal spaces (bone) and in patients with COPD (air)!NOTE: Imaging is difficult in patient with small intercostal spaces (bone) and in patients with COPD (air)!


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Artefacts

Types of ArtefactsTypes of ArtefactsTypes of Artefacts

Near field clutter Side lobe artefact

Reverberation Beam width artefacts

Acoustic shadowing Attenuation artefact

Mirror Imaging/ double images (caused by refraction)Mirror Imaging/ double images (caused by refraction)

Specific FormsSpecific Forms

Side Lobes Reverberations

Beam Width Artefact Incorrect Gain


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When do Artefacts Occur?When do Artefacts Occur?

Good image quality (mirror artefacts)

Poor image quality

Calcification Prothetic material

Tips to Avoid ArtefactsTips to Avoid ArtefactsTips to Avoid Artefacts

Know the pitfallsBeware of strong reflections

Know the anatomy Use multiple views

NOTE: Artefacts are inconsistant!!!NOTE: Artefacts are inconsistant!!!NOTE: Artefacts are inconsistant!!!

Optimizing the 2D Image

Optimization OptionsOptimization OptionsOptimization Options

Gain Depth

TGC Imaging Frequency

Sector width Focus

Post Processing

NOTE: Know your echo machine!NOTE: Know your echo machine!NOTE: Know your echo machine!

Post ProcessingPost Processing

Grayscale Contrast

Compression Maps

NOTE: Use predefined settings for specific situations (i.e. patients difficult to image)NOTE: Use predefined settings for specific situations (i.e. patients difficult to image)NOTE: Use predefined settings for specific situations (i.e. patients difficult to image)


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MMode

MModeMModeMMode

AdvantageAdvantage

High Time resolutionAllows Timing of intervals

Where is it used? (see also Chapter 2)Where is it used? (see also Chapter 2)

Aorta/ left atrium (measurements, opening of aortic valve)

Left/right ventricle (measurements, LV function)

Mitral/Prosthetic valve (type of valve)

Endocarditis (motion of suspected vegetation)

Tricuspid annular plane systolic excursion (TAPSE) for RV function

Mitral valve (Mitral stenosis)

NOTE: MMode has lost a lot of its importance but is still valuable in specific situations!NOTE: MMode has lost a lot of its importance but is still valuable in specific situations!NOTE: MMode has lost a lot of its importance but is still valuable in specific situations!

Other Forms of MModeOther Forms of MModeOther Forms of MMode

Anatomical MMode Freedom of axis

Color Doppler MModeTiming of flow (i.e. flow propagation)

Tissue Doppler MModeMyocardial function, timing of events

Curved MModeDisplay of information (i.e. Strain)


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Spectral Doppler

Doppler Formula

The doppler formula allows us to calculate velocities (i.e. blood) based on the doppler shift between the send and receive signal!

NOTE: The measured velocity greatly depends on the angle between blood flow and the ultrasound beam! Always try to be as parallel as possible!

DopplerDopplerDopplerDoppler

PW - Doppler Low vel. (< 1,5 m/s) site specific

CW - Doppler High vel (> 1,5m/s) site unspecific

Tissue Doppler Lower velocity, higher amplitdueLower velocity, higher amplitdue

AliasingAliasing

Depth Velocity

Width of sample volume Doppler frequency

NOTE: Aliasing will occur if the Nyquist limit is exceeded. The Nyquist limit is qual to one-half of the pulse repetition frequency! Use the baseline shift to “stretch“ the Nyquist limit!




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Tissue Doppler ImagingTissue Doppler Imaging

Velocity Displacement

Strain Strain rate

NOTE: Tissue Doppler is also angle dependent!NOTE: Tissue Doppler is also angle dependent!NOTE: Tissue Doppler is also angle dependent!

Flow Dynamics

Laminar Flow Turbulent Flow

Nonturbulent motion of a fluid in which parallel layers have different velocities relative to each other

Flow of a fluid in which its velocity at any point varies rapidly in an irregular manner

Max. velocity about 1.5 m/s High velocity

Vortex

NOTE: Turbulent flow is usually seen in high velocity flow (i.e. in the setting of stenosis)


A spiral motion of fluid within a limited area



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Bernoulli Equation

The simplified Bernoulli Equation allows an easy estimation of pressure gradients from velocities!

Where can you apply the Bernoulli equation in the Heart?Where can you apply the Bernoulli equation in the Heart?Where can you apply the Bernoulli equation in the Heart?

Direct applications Indirect applications

Valvular stenosis AR Quantification

Defects (i.e. VSD, Coarctation, PDA)

Diastolic function

TR signal (sPAP) dp/dt (contractility)


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Color Doppler

Color EncodingColor Encoding

Flow towards the transducer is coded in red, away from the transducer in blue!Flow towards the transducer is coded in red, away from the transducer in blue!

NOTE: The way flow/ flow velocities are displayed also depends on the color map! Check your machine settings!NOTE: The way flow/ flow velocities are displayed also depends on the color map! Check your machine settings!

Color Doppler and Aliasing

If the Nyquist limit is reached, the color changes abruptly (red to blue, or blue to red). In the color Doppler display, you will see a mosaic pattern!

NOTE: The phenomenon of aliasing provides a good delineation of jets (i.e. PISA)


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Color Doppler Frame RateColor Doppler Frame Rate

Scan line density Emphasis (2D vs. Color)

Sector width (2D) Sector width (Color)

Pulse repetition frequency Depth

NOTE: Always aim for a high color Doppler frame rate!NOTE: Always aim for a high color Doppler frame rate!NOTE: Always aim for a high color Doppler frame rate!


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chapter 1 fact_sheet_-_principles

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