Ebook A practical approach to clinical echocardiography Part 1

Part 1 book A practical approach to clinical echocardiography presentation of content: Echocardiography basic principles, technique, Dis; hemodynamic evaluation by EchoDoppler techniques; mitral stenosis, mitral regurgitation, aortic valve stenosis, tricuspid valve, pulmonary valve, evaluation of prosthetic heart valves,... And other content

Jagdish C Mohan MD DM FASE

Director of Cardiac Sciences

Fortis Hospital Shalimar Bagh, New Delhi, India

Foreword

Bijoy K Khandheria

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A Practical Approach to Clinical Echocardiography

First Edition: 2014

ISBN 978-93-5152-140-2

Printed at:

tips Although there are no separate chapters on transesophageal echocardiography and real-time 3D imaging, these have been well covered in individual sections wherever appropriate The same principle has been applied to contrast echocardiography.

There is little doubt that cardiovascular ultrasound will continue its revolution, and play an important role in the practice of cardiology as well as medicine This book compiled by Prof Jagdish C Mohan is a welcome addition to the various sources of education in this field It is a must-read book for those wishing to practice the art and science of cardiovascular ultrasound

Bijoy K Khandheria MD FACP FAHA FACC FESC FASE

Adjunct Clinical Professor of MedicineUniversity of Wisconsin, School of Medicine and Public Health

Director, Echocardiography Services Aurora St Luke’s Medical Center, Milwaukee, Wisconsin, USADirector, Echocardiography Center for Research and Innovation

Aurora Research Institute, Milwaukee, Wisconsin, USAPast President, American Society of Echocardiography

Former Chair of Cardiovascular Disease, Mayo Clinic, Arizona

Former Professor of Medicine, Mayo Medical School

used this technique year after year for assessment of left ventricular function only Echocardiography represents a strange mixture of several features which have proven prime-time use and an equally numerous techniques which have yet to show clinical utility despite extensive research work spanning decades There is an urgent need to promote that part of science which has robust validation What clinicians require needs to be emphasized with clarity Novices often get unnerved by the available applications on the systems which are more to stand up to the competition rather than

of tangible clinical value However, extensive research has shown applicability of a lot of echocardiographic knowledge and information in day-to-day evidence-based medicine Quantitative and semi-quantitative protocols are gaining ground because these make serial follow-up easily This book is an attempt to make echocardiography simple, practical and easily usable with reproducible data Unnecessary and impractical details have been omitted I would welcome suggestions to make it more readable and meaningful

Jagdish C Mohan

• Hemodynamic Evaluation 24

• Doppler Principle for Estimating Velocity 25

• Ohm’s Law of Fluids (The Hagen–Poiseuille Equation) 27

• The Bernoulli’s Equation 28

• Estimation of Pulmonary Artery Pressures and Pulmonary Vascular Resistance 39

SECtIon 2: Valvular Heart Disease

• Anatomy of the Mitral Valve 45

• Functional Morphology of MR 64

• Anatomy of Trileaflet Aortic Valve 83

• Unicuspid Aortic Valve 85

• Bicuspid Aortic Valve 85

• Quadricuspid Aortic Valve 86

• Anatomy of Aortic Stenosis 86

• Planimetry of the Aortic Valve Area on Aortic Stenosis 87

• Hemodynamics of Aortic Valve Stenosis 88

• Technical Tips 90

• Low-gradient, Low-flow Aortic Valve Stenosis 93

• Paradoxical Low-flow as with Preserved Ejection Fraction 95

• Subaortic Stenosis 95

• Hemodynamics of Aortic Regurgitation 98

• Functional Anatomy of Aortic Regurgitation 100

• Detection of Aortic Regurgitation by Echo-Doppler Techniques 102

• Volumetric Severity of Aortic Regurgitation 104

• Color Flow Doppler Evaluation of Aortic Regurgitation 104

• Aortic Regurgitation Assessment by Vena Contracta 105

• Proximal Isovelocity Surface Area Flow Convergence Method 105

• Diastolic Flow Reversal in the Descending Aorta and Severity of Aortic Regurgitation 106

• Pressure Half-time of Aortic Regurgitation Signal 107

• M-mode Color Flow Propagation Velocity 108

• Summary of Aortic Regurgitation Assessment by Echo-Doppler Methods 108

• Functional Morphology of the Tricuspid Valve 110

• Conditions Affecting Tricuspid Valve 113

• Remodelling in Tricuspid Regurgitation 114

• Functional TR 114

• Organic Tricuspid Valve Disorders 115

• Tricuspid Valve Stenosis 120

• Assessment of Severity of TR 121

• Vena Contracta 121

• Proximal Isovelocity Surface Area Method 122

• Anterograde Velocity of Tricuspid Inflow 122

• Hepatic Vein Flow in Assessment of TR 123

• Anatomy of the Pulmonary Valve 126

• Pulmonary Valve Disorders 127

• Transesophageal Echocardiography in Pulmonary Stenosis 133

• Consequences and Associations of Pulmonary Stenosis 134

• Assessment of Pulmonary Regurgitation 134

• Consequences of Pulmonary Regurgitation 136

• Ball-in-cage Valve 138

• Tilting or Mono-disk Valve 139

SECtIon 3: Systolic and Diastolic Function

• Morphology of the Left Ventricle 165

• Limitations 186

11 Echocardiographic Assessment of Right Ventricular Function:

• Peculiarities of the Right Ventricle 189

• Function Parameters 190

• Right Ventricle Diastolic Function and Pressures 193

• Tricuspid Annular Peak Systolic Velocity 198

• Right Ventricle Strain and Strain Rate Analysis 200

• Physiology of Diastole 204

• Factors Contributing to Diastole 205

• Significance of Diastolic Function 205

• Isovolumic Relaxation Time 206

• Rapid Filling Phase 207

• Deceleration Time of Early Filling Wave (Mitral E- and Pulmonary D-Waves) 207

• Diastasis 208

• Atrial Kick or Contribution 209

• Tissue Motion and Diastolic Function 209

• Left Atrial Volume and Diastolic Function/Dysfunction 210

• How to Perform a Study Focusing on Diastolic Function 211

• Mitral Inflow Velocities 212

• Mitral Annular Velocities 214

• How to Obtain Annular Tissue Velocities 216

• Pulmonary Vein Flow and Diastolic Function 218

• Mitral Flow Propagation by Color M-Mode 221

• Longitudinal Strain, Rotation and Untwisting Rate by Acoustic Speckle Tracking 223

• Diastolic Stress Test 224

SECtIon 4: Muscle Mechanics

• Concept of TDI 229

• Labeling of Tissue Velocity Waveforms 229

• Terms Used in Tissue Doppler Imaging 231

• Technical Details of TDI 231

• Myocardial Velocities in Short Axis 234

• Internal Dependency of Velocities 235

• Fundamental Basis of TDI 236

• Tissue Doppler Data Processing for Deformation Imaging 238

• Clinical Utility of TDI 239

• Prognostic Value of TDI in Diverse Cardiac Disorders 250

• Limitations of TDI 251

• Myocardial Deformation 257

• Descriptive Terms 261

• Acoustic Speckle Tracking 262

• Velocity Vector Imaging 264

• How to Perform Two-Dimensional Strain Imaging? 266

• Effects of Ischemia on Regional Deformation Metrics 268

• Early Systolic Longitudinal Lengthening (Paradoxical Longitudinal Systolic Strain) 269

• Post-systolic Longitudinal Shortening 270

• Paradoxical Strain Patterns 272

• Right Ventricular Deformation 273

• Left Atrial Function by Deformation Imaging 273

• Mechanical Properties of the Aorta 274

• Three-dimensional/Four-dimensional Deformation Imaging 274

• Clinical Applications of Strain and Strain Rate Imaging 276

• Limitations 277

• Fundamentals of Torsion 280

• Echocardiographic Methods of Studying Twist 284

• Clinical Applications of Torsion 285

• Aging and Torsion 286

• Aortic Stenosis, Hypertension and Hypertrophic Cardiomyopathy 286

• Heart Failure 287

• Constrictive Pericarditis 287

• Torsion and Cardiac Resynchronization Therapy 288

• Acute and Chronic Ischemia 289

• Grades of Diastolic Dysfunction and Twist 290

• Carpentier Classification of Ebstein’s Anomaly 306

• Double-Chambered RV 307

• Sinus of Valsalva Aneurysms 308

• Tetralogy of Fallot 311

• Morphological Variants of TOF 312

• Truncus Arteriosus or Common Arterial Trunk 313

• Subaortic Membranous Stenosis 314

• Physiology and Pathology 314

• Transposition of Great Vessels 315

• Structure of Aorta 318

• Parts of Aorta 318

• Functions of Aorta 320

• Normal Aortic Measurements and Imaging Views 321

• Etiopathogenesis of Aortic Disorders 322

• Congenital Disorders of Aorta 322

• Aortic Coarctation 324

• Aneurysm of Sinus of Valsalva 325

• Aortopulmonary Window 329

• Truncus Arteriosus 329

• Supravalvular Aortic Stenosis 330

• Patent Ductus Arteriosus 330

SECtIon 6: Structural Heart Disease

• Myocardial Segment Nomenclature and Coronary Vascular Territory 363

• Right Ventricular Segmentation 363

• Ischemia and Echocardiographic Imaging 365

• Echocardiography in IHD 369

• Evaluation of Myocardial Infarction 369

• Mechanical Complications of Myocardial Infarction 370

• Stress Echocardiography 377

• Cardiac Manifestations of Masses 383

• Cardiac Thrombi and Spontaneous Echo Contrast 384

• European Classification of Cardiomyopathies 397

• Summary of EMF Echocardiographic Features 406

Index 415

Fundamentals of Echocardiography

Chapters

Ö Echocardiography: Basic Principles, Technique,

Echocardiography is a technique of generating images of

the heart with the help of ultrasound (like skiagraphy is

performed with X-rays) Echocardiography has become

an integral part of clinical examination with its bedside

mobility and utility Practice of echocardiography

mandates the following steps:

• Understanding of ultrasound physics

• Knowledge of the instrumentation

• Acquisition skills

• Interpretative skills

• Sound knowledge of cardiovascular anatomy and

physiologies

• Adequate knowledge of common cardiac pathology

• Reporting, storage and retrieval skills

Ultrasound behaves very differently when it passes

through any tissue Many of the objects and artifacts seen

in ultrasound images are due to the physical properties

of ultrasonic beams, such as reflection, refraction,

diffraction and attenuation Indeed, physical artifacts

are an important element in clinical diagnosis (Fig 1.1)

Appreciating the phenomena created by ultrasound may

greatly benefit the patient in terms of increased accuracy

of interpretation and diagnosis The ultrasound wave

created for sending through the tissues is called incident

wave This is the wave whose behavior is changed by the

tissue

ˆ uLtrASound PHYSIcS

Sound

Sound is a form of mechanical energy that consists of waves

of compression and decompression of the transmitting medium, travelling at a fixed velocity (Figs 1.2 and 1.3).Sound is an example of longitudinal waves oscillating back and forth in the direction the sound travels, thus consisting of successive zones of compression

Fig 1.1: Behavior of the sound waves Sound wave after striking a surface gets reflected as well as transmitted into the other medium in a different direction (refracted) Total internal reflection without transmis- sion occurs if it strikes the interface at 90°.

(high pressure) and rarefaction (low pressure) The

medium particles, however, show both longitudinal and

transverse oscillations

Longitudinal oscillations: The oscillating particles

of the medium are displaced parallel to the direction of

motion (direction of energy transfer)

Transverse oscillations: The oscillating particles of the

medium are displaced in a direction perpendicular to the

motion of the wave

Ultrasound: Sound waves with a frequency of 20000

c/s (20 KHz) are labeled ultrasound Ultrasound used in

medical diagnosis has a frequency of 1–10 MHz.1–3 These

are beyond the capacity of human ear to perceive

Why use ultrasound in Medicine?

With higher frequencies (shorter wavelengths), the sound tends to move more in straight lines like electromagnetic beams and is reflected like light beams It is reflected by much smaller objects (because of shorter wavelengths) and hence gives good spatial resolution If the wavelength

of the sound is smaller than the object, no noticeable diffraction occurs

wavelength = speed/frequency

Frequency: The frequency of an ultrasound wave

consists of the number of cycles or pressure changes that occur in one second (Fig 1.2) The units are cycles per second or hertz (Hz) Frequency is determined by the sound source only and not by the medium in which the sound is travelling

Propagation speed: Propagation speed is the rate

at which sound can travel through a medium and is typically considered 1,540 m/s for soft tissue The speed

is determined solely by the medium characteristics like density and stiffness Speed is inversely proportional to density and incompressibility

Pulsed ultrasound: Pulsed ultrasound describes a

means of emitting ultrasound waves from a source To achieve the depth of resolution required for clinical uses, pulsed beams are used Typically, the pulses are a millisecond or so long and several thousands are emitted per second (Fig 1 4)

Ultrasound interaction with tissue: As a beam of

ultrasound travels through a material, various things happen to it A reflection of the beam is called an echo,

Fig 1.2: Alternating compression and rarefaction of a medium as

sound passes through it. Fig 1.3:Compression is accompanied by high pressure and rarefaction by low Sound as an oscillating wave of mechanical energy

pressure.

Fig 1.4: The concept of pulsed ultrasound If an interface is closure

to the source of ultrasound, more pulses will be received per second

resulting in better resolution.

a critical concept in all diagnostic imaging (Fig 1.5) The

production and detection of echoes form the basis of the

technique that is used in all diagnostic instruments A

reflection occurs at the boundary between two materials

provided that acoustic impedance of the materials is

different This acoustic impedance is a product of the

density and propagation speed

If two materials have the same acoustic impedance,

their boundary will not produce an echo If the difference in

acoustic impedance is small, a weak echo will be produced

and most of the ultrasound will carry on through the

second medium If the difference in acoustic impedance

is large, however, a strong echo will be produced If the

difference in acoustic impedance is very large, all the ultrasound will be totally reflected Typically in soft tissues, the amplitude of an echo produced at a boundary is only a small percentage of the incident amplitudes (Fig 1.6)

Strong reflections or echoes show on the ultrasound image as white and weaker reflections as gray (Figs 1.7A and B)

A sound wave will undergo certain behaviors when it encounters a tissue interface Possible behaviors include:

• Reflection off the tissue interface

• Diffraction around the interface

• Transmission (accompanied by refraction) into the interface or new medium (Fig 1.8)

Fig 1.5: The concept of an echo. Fig 1.6: Soft tissue acoustic interface producing some reflection

and more transmission If a medium has high acoustic impedance, stronger reflection will occur.

Figs 1.7A and B: (A) Tissue interfaces with variable acoustic impedance Higher impedance produces brighter echo due to more reflection

of ultrasound; (B) Refraction: Bending of the sound wave as it enters another medium Refraction is associated with decreasing speed and wavelength.

Reflection of sound waves off of surfaces can lead to

one of two phenomena—an echo or a reverberation.

The reception of multiple reflections off of the interface causes reverberations—the prolonging of a sound (Figs 1.9 and 1.10)

Angle of incidence: If a beam of ultrasound strikes the

boundary at right angle, it will be reflected parallel to the transmitting beam and shall produce stronger echo (Fig 1.11) If it strikes a boundary obliquely, the interactions are more complex than for normal incidence (Fig 1.12) The echo will return from the boundary at an angle equal to the angle of incidence The transmitted beam will be deviated from a straight line by an amount that depends on the difference in the velocity of ultrasound

at either side of the boundary This process is known as refraction (Figs 1.1 and 1.7)

Fig 1.8: Decreasing wavelength after refraction in the second medium. Fig 1.9: Multiple linear shadows (arrows) in front of mitral prosthesis in

transesophageal echocardiographic (TEE) view due to rever berations.

Fig 1.10: Reverberations shown by the curved arrow resulting in a

mirror-image artifact.

Fig 1.11: Reflection from a tissue interface at right angle There is stronger reflection resulting in brighter echo Typically, from posterior pericardium.

Fig 1.12: Reflection at an angle equal to the angle of incidence

producing less bright echo.

Reflection is of two types (Fig 1.13):

1 Specular reflection: is from a large tissue interface

(smooth boundary between media) and produces

bright echoes These signals are intense and angle

dependent:

2 Acoustic scattering: occurs from smaller objects

Scattering is responsible for tissue texture The signals

are less intense and less angle dependent These

provide tissue signature to the image

Attenuation

As sound waves travel through a medium (e.g tissue or

blood), the intensity weakens or attenuates The degree

of attenuation is expressed in decibels (dB) Absorption

represents a conversion of sound energy to another

form of energy and is the major reason for attenuation

Attenuation is greater for high-frequency sounds, which

result in higher absorption and more scatter Attenuation

coefficient is smallest for the fat and maximum for lungs

Bones also have very high attenuation coefficient

Penetration

Depth to which an ultrasound beam travels into a tissue

is called penetration Besides the tissue characteristic,

penetration is largely dependent upon the frequency of

the ultrasound being applied:

ˆ uLtrASound BEAM

The sound beam is the confined, directional beam of ultrasound travelling as a longitudinal wave from the transducer face into the propagation medium Ultrasound beams are made of scan lines These have length (azimuth) along their long axis and width (elevation) along their short axis Beam width should be as narrow as possible to prevent beam width artifacts and which can be achieved

by using lens Ultrasound beams are either steered mechanically or electrically Both rapidly sweep sound waves through tissues (Fig 1.14)

Imaging using ultrasound

Image formation requires an ultrasound machine with appropriate transducers and display, using a cathode-ray tube or a flat panel

Fig 1.13: Reflection from a large interface is called specular

reflection and appears bright while smaller objects (smaller than the

wavelength) produce acoustic scattering.

Fig 1.14: Schematic diagram of an ultrasound beam.

A basic echocardiography machine has the following

parts (Fig 1.15):

• Transducer probe: Probe that sends and receives the

sound waves

• Central processing unit (CPU): Computer that does all

of the calculations and contains the electrical power

supplies for itself and the transducer probe

• Transducer pulse controls: Changes the amplitude,

frequency and duration of the pulses emitted from the

transducer probe

• Display: Displays the image from the ultrasound data

processed by the CPU

• Keyboard/cursor: Inputs data and takes measure ments

from the display

• Disk storage device (hard, floppy, CD): Stores the

• Ultrasound transducers, or probes, can be categorized based on their frequency range, low frequency versus high frequency; and the shape of the probe, curved versus linear or sector Linear probes are mostly used for vascular examination while sector probes are used for cardiac examination (Fig 1.17)

• Linear array probes are high-frequency probes frequency probes have less tissue penetration but good near-field image resolution

High-• Curved array probes are low-frequency probes and used mainly for abdominal examination

• Low-frequency probes have greater tissue penetration; however, resolution is compromised (Fig 1.18)

• Ultrasound transducers have a housing that contains inside piezoelectric element

• Main component of a transducer is a piezoelectric element that generates ultrasound waves as it gets deformed by the applied electrical energy As returning ultrasound beam deforms it again, it generates electri-city, which is used to create an image (Fig 1.19)

• Most transducers in use nowadays have synthetic piezoelectrical ceramics, polymers, composites, crystals and so forth, with defined electromechanical coupling and acoustic impedance

Fig 1.15: A schema of an echocardiograph. Fig 1.16: Transducer and its function.

Fig 1.17: Shapes of the transducers.

• The new generations of piezoelectric elements have

broad bandwidth for optimal resolution and

penet-ration (Fig 1.20)

• Nominal frequency of a transducer depends upon its

resonance frequency

• Damping and electrical energy modulation generate a

wide range of frequencies (broad bandwidth) around

the nominal frequency

• Frequency of a transducer depends upon electrical

pulse frequency

• The piezoelectric element has a very high acoustic

impedance and works like a reflective surface but

material surrounding it works as a dump

• The multielement transducer generates a main ultrasound beam that produces diagnostic images and accessory beams (side lobes; Fig 1.21)

Side-lobe beams can produce side-lobe artifacts, which need to be recognized (Fig 1.22) Side-lobes may

be minimized by driving the elements at variable voltages

in a process called apodization

• Most transducers have a focal point Up to the focal point, there is near field and beyond that there is far field Far field has increased distance between scan lines and hence lower resolution

• Currently, most transducers are fully sampled matrix array transducers with thousands of elements

Fig 1.18: Relationship between resolution and penetration of various

transducer probes. Fig 1.19:function as a transducer. Piezoelectric element encased in a housing assembly to

Fig 1.20: Broad bandwidth transducer with a wide range of resonant

frequency.

Fig 1.21: Main ultrasound beam flaked by side lobe beams.

[compared to 64–256 elements in two-dimensional

(2D) probes] that provide a thick ultrasound beam

(Fig 1.23)

• The probe also has a sound absorbing substance, to

eliminate back reflections from the probe itself; and an

acoustic lens, to help focus the emitted sound waves

Despite these, there can be back reflects from the

transducer producing transducer artifacts (Fig 1.24)

• The shape of the probe determines its field of view, and

the frequency of emitted sound waves determines how

deep the sound waves penetrate and the resolution of

the image

• Transducers of high frequency have thin piezoelectric elements that generate pulses of short wavelength

• Beam-forming (link) is a general processing technique

used to control the directionality of the reception or transmission of a signal on a transducer array

Developments in transducer technology have resulted

in a reduced transducer footprint, improved side-lobe suppression, increased sensitivity and penetration, and the implementation of harmonic capabilities that can be used for both gray-scale and contrast imaging

A conventional 2D phased array transducer is posed of multiple piezoelectric elements that are elect-rically isolated from each other and arranged in a single row Individual ultrasound wave fronts are generated by firing individual elements in a specific sequence with a delay in phase with respect to the transmit initiation time Each element adds and subtracts pulses to generate a single ultrasound wave with a specific direction that constitutes

com-a rcom-adicom-ally propcom-agcom-ating sccom-an line The linecom-ar com-arrcom-ay ccom-an be steered in two dimensions [vertical (axial) and lateral (azimuthal)], while resolution in the Z-axis (elevation) is fixed by the thickness of the image slice, which, in turn, is related to the vertical dimension of piezoelectric elements

Three-dimensional echocardiography (3DE) array transducers are composed of 3,000–9,000 indep-

matrix-endent piezoelectric elements with operating frequencies ranging from 2 to 4 MHz and 5 to 7 MHz for transthoracic echocardiography (TTE) and transesophageal echocar-diographic (TEE), respectively These piezoelectric elements are arranged in a matrix configuration within

Fig 1.22: M-mode of aortic root and the left atrium behind it There

is an image of the posterior LV wall seen within the left atrium due to

side lobe error Note that this image is less echogenic than the original.

Fig 1.23: A fully sampled matrix transducer with pyramidal field of view.

Fig 1.24: Transducer artifact near the apex due to back reflects from

the probe.

the transducer to steer the ultrasound beam electronically

The electronically controlled phasic firing of the elements

in that matrix generates a scan line that propagates

radially and can be steered both laterally (azimuth) and

in the elevation to acquire a volumetric pyramid of data

(Fig 1.25)

Multiple-time reception and Parallel

Processing of reflected Beam

Basic imaging by ultrasound uses the amplitude

information in the reflected signal One pulse is emitted,

the reflected signal, however, is sampled more or less

continuously (99% time is for receiving) As the velocity

of sound in tissue is fairly constant, the time between

the emission of a pulse and the reception of a reflected signal is dependent on the distance; that is, the depth

of the reflecting structure The reflected pulses are thus sampled at multiple time intervals (multiple range gating), corresponding to multiple depths, and displayed

in the image as depth Parallel processing for multiple simultaneous reception of reflected waves improves the temporal resolution (Fig 1.26) This parallel processing could be in ratio of 1:16 or more

Spatial resolution

It is the parameter of an ultrasound imaging system that characterizes its ability to detect closely spaced interfaces and displays the echoes from those interfaces as distinct and separate objects If resolution is better, clarity of the image is improved Resolution is of two types:

Axial resolution: Is the minimum required reflector

separation along the direction of propagation required

to produce separate reflections Good axial resolution is achieved with short spatial pulse lengths Short spatial

pulse lengths are a result of higher frequency and higher

damped transducers Therefore, the higher the frequency,

the better is the resolution (Fig 1.27) Axial resolution is also called longitudinal or azimuthal resolution

Lateral resolution: Is the minimum reflector separation

perpendicular to the direction of propagation required

to produce separate reflections Good lateral resolution

is achieved with narrow acoustic beams Wider beams typically diverge further in the far field and any ultrasound beam diverges at greater depth, decreasing lateral

Fig 1.25: The technique of obtaining pyramidal data set with use of a

matrix array transducer. Fig 1.26:channels for a single transmitted beam. Parallel processing of multiple reflected beams in several

Fig 1.27: Axial versus lateral resolution.

resolution Therefore, lateral resolution is best at shallow

depths and worse with deeper imaging

Temporal resolution: is the ability to detect that an

object has moved over time For the purposes of medical

ultrasound, temporal resolution is synonymous with

frame rate Typical frame rates in echo imaging systems

are 30–100 Hz The temporal resolution or frame rate = 1/

(time to scan 1 frame) The time to scan one frame is equal

to the pulse repetition period number of scan lines per

frame

Common means of improving frame rate include:

• Narrowing the imaging sector, which decreases the

time it takes to scan one frame

• Decreasing the depth, which decreases the pulse

repetitive frequency

• Decreasing the line density, which requires fewer lines

to scan one frame

• Turning off multifocus, which decreases the number of

pulses needed per line

Focusing

Within transducers, there is a FOCUS that concentrates

the sound beam into a smaller beam area than would

exist otherwise This area of focus is where one obtains the

best images The focus is on the monitor, on the vertical

millimeter scale So when positioning anatomy, make

sure it is in the region of the focus, so best images may be

obtained

It is defined as the peak rarefactional pressure (negative pressure) divided by the square root of the ultrasound frequency The used range varies from 0.05 to 1.9

technique of Image Acquisition

• At the start of an echocardiography examination, the appropriate transducer is selected according to the type of examination and patient’s body habitus

• A higher frequency transducer provides better resolution, but it has a shallower depth of penetration For the pediatric population, the transducer frequency

is usually 5–7.5 MHz, but for adults the transducer frequency at the start of an examination is usually 2–2.5 MHz

• In fundamental imaging, echocardiographic images are created when the transducer receives reflected beams of the same frequency as the transmitted beam, but the interface between tissue and blood can

be delineated better with the reception of harmonic frequencies

• When the only reflected frequency received to create the ultrasound image is equal to a multiple of the transmitted frequency, the technique is called harmonic imaging Myocardial tissues are able to generate harmonic frequencies, and harmonic imaging improves the delineation of the endocardial border (tissue harmonic imaging) As a result, harmonic imaging is usually the imaging modality of choice (Fig 1.28)

• A limitation of harmonic imaging in routine 2D echocardiography is the increased sparkling quality to the ultrasound image and the increased thickness of the endocardial border (Fig 1.29)

• The following should be shown on the screen: The

patient’s identification, blood pressure at the time of the examination, and an electrocardiographic tracing

• The examination of an adult patient usually begins with a depth of 20–25 cm and a wide sector (90°) This also gives an idea about any unusual extracardiac structures After the initial view, adjust the field depth

to use the entire screen to demonstrate the intended cardiovascular images

• A zoom or regional expansion selection (RES) function should be used frequently to visualize a region of interest The zoomed image is also better for

Fig 1.28: Improved signal-to-noise ratio with harmonic imaging

compared to fundamental imaging.

making measurements, with less intraobserver and

interobserver variability (Fig 1.30)

• When quantitative measurements are made, review

the acquired image in a cine loop format to identify a

frame at a specific timing of a cardiac cycle Examples

are a midsystolic frame to measure the diameter of the

left ventricular outflow tract, an end-systolic frame to

measure the size of the left atrium and an end-diastolic

frame to measure the wall thickness of the left ventricle

Improving temporal resolution

Specific areas need to be imaged and it may be necessary

to decrease the sector size, which will improve temporal

resolution by increasing the frame rate The gain of the image is controlled by overall gain and regional gain [by time gain compensation (TGC)]

tissue texture

Hyperechoic areas have a great amount of energy from

returning echoes and are seen as white

Hypoechoic areas have less energy from returning

echoes and are seen as gray

Anechoic areas without returning echoes are seen as

black

time Gain compensation

The received ultrasound signal can be amplified by increasing the gain Decreased gain yields a black image and details are masked, while increased gain yields a whiter image

TGC will change the gain factor so that equally reflective structures will be displayed with the same brightness regardless of their depth (Fig 1.31)

TGC allows amplification of ultrasound beams from deeper depths because different amplitudes of ultrasound signals are produced when received from different depths More TGC is required for higher frequency transducers, which create more attenuation

Returning ultrasound waves are referred to as signal, while background artifact is referred to as noise Increasing the gain increases the signal-to-noise ratio

Fig 1.29: Note thickness of the chordae tendineae in harmonic

imag-ing at 1.3 MHz compared to fundamental imagimag-ing at 1.9 MHz All other

parameters are unchanged.

Fig 1.30: Zoom view of the mitral valve to measure the size of annular caseoma.

Fig 1.31: Time gain compensation (TGC) is mounted on the knob

panel of the echocardiograph.

Reduces the differences between the smallest and largest

amplitudes of ultrasound images by reducing the total

range without altering the signal ratio

Side Lobe Artifacts

The probe cannot produce a pulse that travels purely in

one direction Pulses also travel off at specific angles These

side lobes are relatively weak and so normally do little

to degrade the image Their effect is only normally seen

faintly superimposed in fluid filled areas that are anechoic

and so do not obscure the weak side lobe reflections The

exception is when a side lobe strikes a particularly strong

reflector at 90° In this case, the reflector can appear within

the image

Partial volume: The slice that makes up the ultrasound

image is 3 dimensional This typically means that fluid

filled areas, where they are very small or adjacent to

soft tissue will not appear anechoic (black) as would be

expected, but often contain low level echoes which can be

mistaken for debris or even soft tissue

Acoustic Shadowing

Tissues with high attenuation coefficients like bone or

prosthesis do not allow passage of ultrasound waves

Therefore any structure lying behind tissue with a high

attenuation coefficient cannot be imaged and will be seen

as an anechoic region (Fig 1.32)

Echocardiographic display

Reflected ultrasound waves (echoes) are detected, filtered and amplified electronically by the system and displayed

on the cathode ray tube in the following manner.4–6

A-mode and M-mode image: Sending and receiving an

ultrasound wave along a single line generates an A-mode (amplitude-mode) or an M-mode image In amplitude mode (A-mode), reflected sound signal is displayed as a vertical spike (voltage amplitude)

In brightness mode (B mode), the amplitude spike is replaced by a dot The dot has a location, certain brightness and also motion Dots of a structure or interface have similar brightness and motion, which can be displayed in two axes: vertical and horizontal If there are dots along a single scan line, it is called M-mode echocardiography

If dots are along multiple scan lines that are steered in a predetermined fashion, the morphology of the structure can be identified when dots are arranged in a plane and this is called cross-sectional or 2D echocardiography “Motion imaging mode (M-mode) is a gray-scale display of amplitude from each depth along a single scan line over time with a high temporal resolution” (Figs 1.33 and 1.34)

2D image is a gray-scale display of amplitude (dots)

from each depth along several scan lines created by steering the ultrasound beam in an imaging plane This provides a real-time tomographic view in the form of a thin slice with spatial resolution at the cost of temporal resolution (Figs 1.35 and 1.36)

Fig 1.32: Acoustic shadow (arrow) due to metallic aortic prosthesis. Fig 1.33: M-mode echocardiogram through the basal part of the LV

Structures are identified by motion patterns.

These slices are of less than 1 mm each and can be sagittal, coronal, transverse or oblique.7

3D image is a colorized-display of amplitude over

depth from several imaging planes in a pyramidal volume

as if tomographic slices in various X, Y and Z planes have been stitched together (Figs 1.37 and 1.38)

Real-time 3D images are obtained by matrix array transducers (Fig 1.39)

Fig 1.34: M-mode echocardiogram at the level of aortic valve. Fig 1.35: Two-dimensional echocardiographic long axis view.

Fig 1.36: Two-dimensional echocardiographic view perpendicular to

the long axis as shown in Figure 1.35. Fig 1.37:of length, width and depth. Three-dimensional echocardiographic view with perception

Fig 1.38: Longitudinally reconstructed image from a 3D pyramidal

volume Part of the pyramidal volume is appreciated.

• Parasternal (anterior chest wall on either side of

sternum between second and 4th intercostal spaces)

• Apical (over palpable apex)

• Subcostal (below xiphisternum)

• Suprasternal (above manubrium sterni in suprasternal

notch)

• Transesophageal

• Epicardial (during open heart surgery)

• Intracardiac

Axis: is the plane in which the ultrasound beam travels

through the heart:

Long axis: When the ultrasound beam travels

longitudinally through the heart (Fig 1.40)

Short axis: Short axis image is obtained when the

ultrasound beam travels perpendicular to the long axis of

the heart (Fig 1.41)

Views: are window-specific images like apical

four-chamber view or parasternal long axis (PLAX) view or suprasternal view (Fig 1.42)

Sequence of an Echocardiographic Examination

Sequence of an echocardiographic examination is different in adults and children with suspected congenital heart disease In infants and children, the primary window

is subcostal followed by suprasternal with a little use of parasternal views In adults, the following sequence of windows for examination, is usually followed (Fig 1.43):

• Left parasternal window

• Apical window

• Subcostal window

Fig 1.39: Arrangement of piezoelectric elements in a matrix

tansducer shown in a cross-section view.

Fig 1.40: Long axis view.

Fig 1.41: Short axis image (left lower inset) Right panel shows

position transducer. Fig 1.42:sternal notch and oriented anteriorly to obtain long axis view of aorta. Suprasternal view with transducer placed in the

supra-• Suprasternal window

• Right parasternal window

To obtain an image, it is common to rotate, tilt or

move the transducer in different directions to get the best

possible views

Parasternal Long Axis View

In this view, ultrasound beam goes through the long axis

of the heart The transducer is placed in the left second to

fourth intercostal space close to the sternum The view and

the structures that it shows are depicted in Figure 1.44

Fig 1.43: Echocardiographic windows and the orientation of the transducer.

Fig 1.44: Parasternal long axis view showing left ventricle (LV); right

ventricle (RV); aortic root (AO); left atrium (LA); thoracic aorta (TA);

mitral valve (MV); aortic valve (AV).

Fig 1.45: Long axis view of the right ventricular outflow tract (RVOT) and the pulmonary artery (PA).

In the left parasternal view, tilting the transducer superiorly and laterally will show the right ventricular outflow tract and the pulmonary artery in the long axis view (Fig 1.45)

Parasternal Short Axis View

From the PLAX view, the transducer is rotated counterclockwise to right angle and tilted up and down

to obtain short axis views at various levels (Figs 1.46

to 1.48)

Apical Window

The transducer is placed at the palpable apex or just below

and 4 views can be obtained by rotating and tilting it

1 Apical four-chamber view

2 Apical two-chamber view

3 Apical long axis view

4 Apical five-chamber view

Apical four-chamber view is obtained when the

transducer is placed at the apex and the reference point

toward the right shoulder (Fig 1.49)

When the transducer from the apical four-chamber

position is rotated anticlockwise, apical two-chamber

view can be obtained (Fig 1.50)

Fig 1.46: Parasternal short axis view at mid-LV level. Fig 1.47: Parasternal short axis view at the level of aortic valve.

Fig 1.48: Parasternal short axis view at the level of mitral valve (MV). Fig 1.49: Apical four-chamber view and the structures shown.

Rotating the transducer clockwise from the apical four-chamber position shows apical long axis view (Fig 1.51)

With inferior tilt of the transducer from the apical chamber view, an apical five-chamber view can be shown (Fig 1.52)

Subcostal Window

By placing the transducer in subxiphoid position, subcostal views can be obtained both like that from parasternal and apical windows The transducer needs

to be rotated or tilted Most standard views like the chamber view (Fig 1.53) or the short axis views can also be

four-Main structures examined by subcostal views besides the cardiac chambers are:

• Inferior vena cava

• Hepatic veins

• Azygous and anomalous pulmonary veins

• Abdominal aorta and its branchesThe four cardiac chambers, the right ventricular outflow tract, the aorta, and the vena cava can be visualized in the subcostal view Sometimes, it is also possible to visualize

a portion of the abdominal aorta Pointing the transducer toward the right side of the patient would result in a good view of showing the liver and suprahepatic veins as well

as a transverse cross-section of the inferior vena cava (Fig 1.55)

Fig 1.50: Apical two-chamber view with structures shown. Fig 1.51: Apical long axis view.

Fig 1.52: Apical five-chamber view. Fig 1.53: Subcostal four-chamber view (left upper corner) and the

schema (lower left corner).

obtained from a subcostal transducer position The

sub-costal view can be very helpful in patients with bad image

quality or in patients with suspected pericardial effusion

To obtain the subcostal four-chamber view, place the

transducer over the center of the epigastrium and tilt it

downward from the suprasternal notch to the left shoulder

of the patient The image produced will be similar to the

apical four-chamber view The short-axis subcostal view,

however, is similar to the parasternal view and is ideal for

studying the right side of the heart

Subcostal four-chamber view is obtained by pointing the

reference point of the transducer toward the left shoulder

with some inferior tilt to the base of probe By rotating the

transducer, a series of short axis can be obtained (Fig 1.54)

Suprasternal View

Suprasternal views (Fig 1.56) are routinely used in

children and adult patients to study:

• Ascending aorta; arch and its branches; descending

thoracic aorta

• Coarctation of aorta

• Patent ducts arteriosus

• Right and left superior vena cavae

• Azygous veins

• Supracardiac variety of anomalous pulmonary venous drainage

• Pulmonary artery bifurcation

transesophageal Echocardiographic Views

The technique of TEE permits visualization of heart without the acoustic interference imposed by the chest wall, ribs and the lungs This is achieved by introduction of

Fig 1.54: Subcostal short axis view showing the entire right heart

structures.

Fig 1.55: Longitudinal view of the inferior vena cava (IVC) from the subcostal view.

Fig 1.56: Suprasternal long axis view showing aorta and bifurcation of

the pulmonary artery Segmental branches of the left pulmonary artery

(LPA) are also seen Right pulmonary artery (RPA).

Fig 1.57: The procedure of TEE in a schematic diagram The probe

is flexible and can be rotated and flexed or retroverted with knobs at the handle.

Fig 1.58: Transverse midesophageal four-chamber view (4CV). Fig 1.59: Vertical or Longitudinal midesophageal two-chamber

High esophageal views are for visualizing the great vessels (Fig 1.65) while the transgastric views are used to study the detailed anatomy of the mitral and aortic valves including continuous wave (CW) interrogation of the left ventricular outflow tract

Details of TEE examinations are shown in respective chapters

interference

Its drawbacks are:

• Semi-invasive and hence needs intensive monitoring

• Novel imaging planes need greater technical skills to

interpret

• Not possible in uncooperative patients or those with

esophageal stricture, cervical arthritis, gastric ulcer

and so forth

tEE Probe Manipulation

Probe movements (entire probe moves):

• Advance or withdraw

• Turn right or left

Fig 1.60: Midesophageal long axis view showing aorta, left atrium, left

ventricle and the mitral valve. Fig 1.61:aortic valve, atria and the RVOT. Transverse midesophageal view to show interatrial septum,

Fig 1.62: TEE RV inflow view showing tricuspid valve. Fig 1.63: Midesophageal bicaval view showing inferior and superior

vena cavae and the interatrial septum.

Fig 1.64: Midesophageal transverse short axis view showing left atrial

appendage (LAA). Fig 1.65:beyond the sinotubular junction. High esophageal view showing ascending aortic dissection