Two-dimensional echocardiography uses ultrasound to generate dynamic images of the heart. It works by transmitting ultrasound pulses that reflect off tissues and return to the transducer. The document discusses key topics in ultrasound physics including: how sound waves propagate and interact with tissues through reflection, refraction, scattering and attenuation; transducer design and beam formation; and Doppler techniques for assessing blood flow. It provides technical details on how 2D echocardiography images are formed and displayed to evaluate cardiac anatomy and function.

1. Kangkan sharma
Principles and Technology of
Echocardiography

2.  TWO-DIMENSIONAL ECHOCARDIOGRAPHY
GENERATES DYNAMIC IMAGES of the heart
from reflections of transmitted ultrasound.
successful cardiac imaging requires a firm
understanding of the interactions
 of sound and tissue

3. PHYSICAL PROPERTIES OF
SOUND WAVES
 Vibrations-Sound is the vibration of a physical
medium. In clinical echocardiography, a
mechanical vibrator, known
 as the transducer, is placed in contact with the
esophagus (transesophageal echocardiography
[TEE]),
 skin (transthoracic echocardiography), or the
heart (epicardial echocardiography) to create
tissue vibrations.
 The resulting tissue vibrations or sound waves
consist of areas of compression (areas where
molecules

4.  Amplitude-The amplitude of a sound wave
represents its peak pressure and is appreciated
as loudness. The level of
 sound energy in an area of tissue is referred to as
intensity

6.  Frequency and Wavelength
 Sound waves are also characterized by their
frequency ( f ), or pitch, expressed in cycles per
second, or Hertz
 (Hz), and by their wavelength (λ). These
attributes have a significant impact on the depth
of penetration of
 a sound wave in tissue and the image resolution
of the ultrasound system.

7.  Propagation Velocity
 The travel velocity or propagation velocity of
sound (v) is determined solely by the medium
through which it passes. For example, the speed
of sound in soft tissue is approximately 1,540
m/s.
 Velocity can be calculated as the product of
wavelength and frequency:
 v = λ × f
 It becomes apparent that the wavelength and
frequency are necessarily inversely related:
 λ = v × 1/f
 λ = (1500 m/s)/f

8. INTERACTIONS OF SOUND AND
TISSUE
 1. Reflection
 2. Refraction
 3. Scattering
 4. Attenuation

10.  Reflection
 Echocardiographic imaging depends on the
transmission and subsequent reflection of ultrasound
energy
 back to the transducer. A sound wave propagates
through uniform tissue until it reaches another tissue
 type with different acoustic properties. At the tissue
interface, the ultrasound energy undergoes a dramatic
 alteration, after which it can be reflected back toward
the transducer or transmitted into the next
 tissue, often in a direction that deviates from the original
course. Precisely how the ultrasound beam will
 be affected is predicted by factoring the acoustic
properties of the tissues that create the interface and
the

11.  The Tissue Interface: Acoustic Impedance
 An important acoustic property of a tissue is its
capacity for transmitting sound, known as
acoustic impedance
 (Z). This property is largely related to the density
(ρ) of the material and the speed which
ultrasound travels (v):
 Z = ρ × v

12.  When sound reaches an interface of two tissues
of similar acoustic impedance, the ultrasound
beam
 travels across the interface largely undisturbed.
When the tissues differ in impedance, a
percentage of the
 ultrasound energy is reflected and the remainder
is transmitted. The larger the absolute difference
in the levels
 of acoustic impedance across the interface, the
greater the percentage of the ultrasound energy
that is reflected.

13.  Reflection can be calculated by using the
reflection coefficient (R):

14.  Specular and Scattering Reflectors
 The reflection of sound is also greatly affected by
the size and surface of the tissue. Two types of
reflection,
 Specular and scattered, are commonly
encountered.
 Specular reflection occurs when a sound wave
encounters a large object with a smooth surface.
Such surfaces act like an acoustic mirror,
generating strong reflections that travel away
from the interface at an angle equal and opposite
to that at which the ultrasound beam traveled to
the interface

15.  Scattering reflection occurs when an ultrasound beam
encounters small or irregularly shaped surfaces. Such
small objects, such as red blood cells, scatter
ultrasound energy in all directions, so that far less
energy is reflected back to the transducer than in the
case of a specular reflector. This type of reflection is
the basis of the Doppler analysis of red blood cell
movement.
 Both types of reflection contribute to the two-
dimensional image. Although the strongest signals
and best
 images are obtained from interfaces that are
perpendicular to the beam orientation, cardiac tissue
is to a
 large extent irregular and nonlinear in shape.
Therefore, a significant component of the reflected
energy

16.  Refraction
 The portion of the ultrasound beam that is not
reflected propagates through the interface, but its
direction is often altered or refracted. Refraction
is most pronounced when the difference in sound
velocities in the two tissues is large and the angle
of incidence is acute

17.  Attenuation
 In addition to being reflected and refracted from
tissue interfaces, the ultrasound signal is altered
as it travels through uniform tissue. Most notable
is the steady loss (i.e., attenuation) in transmitted
intensity as a consequence of dispersion and
absorption.

18. TRANSDUCER DESIGN AND
BEAM FORMATION

19.  1. A ceramic piezoelectric crystal, which acts as an
ultrasonic vibrator and receiver
 2. Electrodes, which both conduct electric energy to
stimulate the piezoelectric crystal and record the
 voltage from returning echoes
 3. Backing, which acts to dampen the vibrations of the
crystal rapidly
 4. Insulation, which prevents unwanted vibration of
the transducer from standing waves or extraneous
 incoming waves
 5. A faceplate, which optimizes the acoustic contact
between the piezoelectric crystal and the esophagus.
The faceplate may also include an acoustic lens to
focus the beam

20. The Three-dimensional Ultrasound
Beam

21.  Most commonly, ultrasound beams have either a
disk or rectangular shape and
 comprise two main zones: The near field
(Fresnel) and far field (Fraunhofer) zones. Beam
manipulation and
 image resolution are greatest within the near
field. Also, ultrasound energy is more
concentrated within
 this zone, yielding stronger echoes and better
imaging.

22.  Focusing
 Focusing can further narrow the ultrasound
beam. This is accomplished in three ways, as
follows:
 1. By creating a concave shape in the
piezoelectric crystal
 2. By gluing an acoustic lens to the front of the
crystal
 3. Electronically with the use of phased array
transducers

23.  Electronic Beam Focusing: The Phased Array
 Modern echocardiography systems allow the
echocardiographer to adjust the depth of the focal
zone selectively to optimize image quality. A single
element transducer emits a wave front that diverges
in a hemispheric pattern.
 By aligning several crystals side by side in a linear
array, the interaction of the individual sound waves
emitted by each crystal creates a narrow, forwardly
directed wave front .
 The beam’s shape can be focused further by
electrically activating the crystals at the ends of the
array before those located at the center creating a
concave wave front thereby focusing the beam at a
selected distance from the transducer face

24. Resolution
Axial Resolution
 Axial resolution is the ability of the ultrasound system
to identify two separate objects that lie along the
 path of the ultrasound beam axis
Lateral (Azimuth) Resolution
 Lateral resolution is the ability of the ultrasound
system to distinguish between objects that are
horizontally
 aligned and perpendicular to the path of the
ultrasound beam
Elevational Resolution
 Elevational resolution is the ability of the ultrasound
system to distinguish between objects that are
vertically
 aligned and perpendicular to the emitted ultrasound
beam

25. DISPLAY FORMATS

26.  The Golden Rule: Time is Distance
 Ultrasonic imaging is based on the amplitude and time delay of
the reflected signals (Fig. 1.10). Since the
 velocity in tissue is relatively constant, only the distance of the
structure from the transducer alters the time
 required for the ultrasound wave to travel to and from the
reflected structure:
 Distance = velocity × time (9)
 As sound travels at a rate of 1,540 m/s through soft tissue, the
round trip travel time for each centimeter
 of separation between transducer and reflector is calculated as:
 Travel time = 13 μs/cm (10)
 By timing the interval between transmission and return of the
reflections, the echocardiography system
 can precisely calculate the location of a structure.

27.  Amplitude Mode
 The original display format is amplitude mode (A-
mode), in which the amplitudes of the returning
signals
 are represented as a series of horizontal spikes
along the vertical axis of the display. The
horizontal spikes
 correspond to the distance of the reflecting tissue
and the strength of the returning echoes

28.  Brightness Mode
 Current imaging is based on brightness mode (B-
mode) technology. Instead of horizontal spikes,
the amplitudes
 of the returning echoes are represented as pixels
of varying brightness along the vertical axis of the
display.
 The brightness correlates with the strength of the
returning signal

29.  Motion Mode
 Motion mode (M-mode) adds temporal
information to B-mode by displaying a series of
collected B-mode images.
 M-mode echocardiography provides a one-
dimensional, “ice pick” view through the heart and
updates the B-mode images at a very high rate,
allowing dynamic real-time imaging
 However, M-mode imaging displays only axial
motion and provides a limited view of cardiac
anatomy.
 Because of its superior dynamics and axial
resolution, M-mode is the best mode for
examining the timing of cardiac

30.  Two-dimensional Echocardiography
 Two-dimensional echocardiography is a
modification of B-mode echocardiography and the
mainstay of the echocardiographic examination.
 Instead of repeatedly firing ultrasound pulses in a
single direction, the transducer in two-
dimensional echocardiography sequentially
directs the ultrasound pulses across a sector of
the cardiac anatomy.
 In this way, two-dimensional imaging can display
a tomographic section of the cardiac anatomy,
and unlike M-mode, it can show shape and lateral
motion

31.  TWO DIMENSIONAL SCAN SYSTEMS
Linear Scanners
 The linear scanner uses a long transducer composed of
several crystals.
 Groups of crystals are activated sequentially from one end of
the transducer to the other.
 The firing of each group of crystals images the structures
directly in front of them.
 With sequential firing of the groups of crystals, the anatomic
features
 under the entire transducer are imaged.
 However, the disadvantage of this approach is that the
transducer
 face must be large enough to cover a broad anatomic area

32.  Sector Scanners
 The phased array sector scanner is most commonly
used in echocardiography.
 This is an electronic system that by precisely timing the
activation of the individual transducer elements is able
to sweep the sound beam in an arc across a
predetermined field.
 With activation of the transducer elements in different
sequences, the ultrasound beam in the phased array
system can be easily narrowed, steered, and focused .
 The ability to direct a series of beams electronically
over an arced sector also makes it possible to use the

33. CREATING THE TWO
DIMENSIONAL IMAGE
 Imaging a Sector
 To construct the two-dimensional image, the
echocardiographic system records the B-mode data
from the
 first pulse, redirects the next beam, records the
returning signals, and so on until the entire sector has
been scanned. The orientation of each B-mode line
(also called the scan line) is recorded so that the
information can be displayed in the correct position on
the display screen.
 Each image created by a sector scan is a frame.
 Two-dimensional imaging typically requires 100 to 200

34.  Image Quality and Dynamic Motion
The pulse repetition frequency is the rate at which
sound pulses are transmitted per second. The greater
 the pulse repetition frequency, the greater the number of scan
lines that are emitted in a given period of
 time.
The frame rate is the frequency at which the sector is
rescanned. Each frame consists of one or two scans
 across the sector of interest. The information from two sweeps
can be interlaced to improve image quality. A high frame rate
improves the capture of movement. Typically, a frame rate
greater than 30/s allows the dynamic representation of some
relatively fine movements (e.g., intermediate positions of the
aortic valve).
The scan line density, calculated as the number of lines
per degree of the sector, greatly affects the image quality.

35.  Image Quality Versus Dynamic Motion
 It quickly becomes apparent that the
echocardiographer must choose between the size
of the imaging field and the frame rate.
 If the frame rate is high (100 frames/s), the
number of scan lines per frame is reduced,
resulting in a lower line density. Although the
dynamics of the image may be excellent, the
spatial image quality is decreased.

36. Doppler technology and
techniques
 two-dimensional imaging is unable to visualize
blood flow
 Doppler ultrasonography overcomes this
limitation in the assessment of blood flow. Its
color flow display affords the echocardiographer
dramatic views of blood flow.
 In addition, spectral Doppler provides the tools to
quantify the magnitude and direction of flow.
Since Doppler evaluation is quantitative, it
provides a means of grading the severity of
disease in many cases.

37. DOPPLER FREQUENCY SHIFT
 The Doppler Effect first described by Austrian
physicist Christian Doppler

38. Signal Frequency and Blood
Flow
 Red blood cells reflect ultrasound as they travel
through the blood stream.
 By directing an ultrasound signal at flowing blood
and listening for the change in frequency
produced by the red cell reflections, Doppler
echocardiography can assess the direction and
speed of blood flow.

40.  If the red cells are stationary, the signal is reflected at
the same frequency as the transmitted signal. Since no
Doppler frequency shift occurs, the situation is similar to
that of two-dimensional echocardiography.
 When blood flows toward the ultrasound transducer, the
reflected signal is compressed by the motion of the red
cells, and its frequency is higher than that of the
transmitted signal.
 Conversely, when blood flows away from the ultrasound
transducer, the frequency of the reflected signal received
by the transducer is
 lower than that of the transmitted signal.
 The technical term for the alterations in the frequency of
the
 ultrasound signals caused by the Doppler effect is
modulation. Through analysis of the modulated signal,

41. DOPPLER ANALYSIS
 The Doppler Equation: Linking the Frequency
Shift to Velocity
 The Doppler equation describes the relationship
between the alteration in ultrasound frequency
and blood
 flow velocity (Fig. 5.2): Δf = v × cos θ × 2ft/c
 where Δf is the difference between transmitted
frequency ( ft) and received frequency, v is blood
velocity, c is the speed of sound in blood (1,540
m/s), and θ is the angle of incidence between the
ultrasound beam and blood flow

42. Blood flow velocity calculation

43. Implications of Beam
Orientation
 Most Doppler systems default to a value of cos θ
of 1, with the assumption that the
echocardiographer has directed the ultrasound
beam to be nearly parallel with the blood flow of
interest.
 This approach has the advantages of stronger
Doppler signals and a lower rate of errors as a
consequence of the plateau shape of the cosine
curve at angles of low incidence. Therefore, in
clinical practice, the transducer should be
positioned such that the beam and blood flow are
nearly parallel for accurate velocity calculations

44. Clinical limitations TEE Doppler
Examinations
 Unlike the position of a transthoracic probe, which
can be moved freely about the chest wall to
achieve proper orientation, the position of the
TEE probe is limited to the confines of the
esophagus and stomach
 The standard views used for two-dimensional
imaging are often inadequate for Doppler
assessments

45. Isolating the Doppler Frequency
Shift

46. PRESENTATION OF DOPPLER
DATA
Audible Broadcast
Spectral Display

47. DOPPLER TECHNIQUES
 Pulsed Wave Doppler The pulsed wave
transducer uses a single crystal as both the
emitter and the receiver of ultrasound waves.
 Like the pulsed echo system described for two-
dimensional imaging, the pulsed wave Doppler
system transmits a short burst of ultrasound
toward the target and then switches to receive
mode to interpret the returning echoes. Since the
speed of sound (c) in tissue is constant, the time
delay for a signal to reach its target and return to
the transducer depends solely on the distance (d)
to the target:
 Time delay = 2d/c

48. Clinical Caveats for Pulsed Wave
Doppler
 Since red cells scatter the ultrasound signal, the reflected
Doppler signal returning to the transducer represents only
a fraction of the transmitted signal. Therefore, the returning
signal is much weaker than the strong specular reflections
from tissue interfaces. Accordingly, the clinician faces a
trade-off between good range resolution (i.e., a small
sample length) and an accurate determination of velocity.
 In contrast to the preferred settings in two-dimensional
echocardiography, in which axial resolution is a priority and
the pulse length is kept very short, large Doppler sample
volumes (length >10 mm) are preferred by most
echocardiographers to improve the accuracy of the velocity
measurement because they provide more wavelength for
demodulation. A more powerful Doppler signal is produced
because the signal-to-noise ratio is increased.

49. Pulsed Wave Doppler System
Processing
 The rate at which the device repeatedly
generates sound bursts is known as the pulse
repetition frequency (PRF).
 The longer the pulsed wave system waits for the
returning echoes, the lower the PRF. Since the
speed of sound through tissue is a constant, the
PRF is directly related to the depth of the sample
volume.

50. Limitations of Pulsed Wave
Doppler
 Since the Doppler data are collected intermittently, the
maximal frequency and blood flow velocity that
 can be accurately measured by pulsed wave Doppler
are limited.
 The maximal frequency, which equals one-half the
PRF, is known as the Nyquist limit. At Doppler shifts
above the Nyquist limit, analysis of the returning
signal becomes ambiguous, so that the velocity is
indeterminate. This ambiguous signal for frequencies
above the Nyquist limit, known as aliasing, appears
on the spectral display as a signal on the other side of
the baseline, often referred to as wraparound (The
intermittent sampling of the pulsed system can
resolve only frequencies that are less than half the
pulse repetition rate

51. Maximizing Pulsed Wave Velocity
Measurements
1Lessening the target distance increases the PRF,
thereby increasing the velocity that can be
assessed
2select a low transmitted frequency
 3set the baseline of the spectral display to
provide the greatest range of velocities in the
direction of interest.

52. Continuous Wave Doppler
 The continuous wave Doppler technique avoids the
maximal velocity limitation of pulsed wave systems.
The transducer of a continuous wave system is
composed of two crystals, one continuously
transmitting and the other continuously receiving the
reflected ultrasound signal. With continuous reception
of the Doppler signal, the Nyquist limit is not
applicable, and blood flows with very high velocities
can be recorded accurately.
 A continuous wave transducer can measure velocities
in excess of 7 m/s and is
 Unlike the clean envelope achieved with pulsed wave
Doppler, the spectral display of continuous wave
Doppler is typically shaded with the multitude of
velocities recorded along the beam path

53. Color Flow Mapping
 Color flow mapping provides a dramatic display of
both blood flow and cardiac anatomy. To achieve
these remarkable images, the technique combines
two-dimensional ultrasonic imaging and pulsed wave
Doppler methods
 In the most widely accepted color code, red indicates
flow toward the transducer and blue indicates flow
away from the transducer.
 Increasing flow velocities are displayed by various
hues; high-velocity flow toward the transducer is
displayed as yellow, and high velocity flow away from
the transducer is displayed as cyan.
 Flow with directional variance, as in areas of
turbulence, is displayed as green.

54. Thank you