Recent advancements in ultrasound technology and principle behind doppler ultrasound is discussed here.

1. Sudil Paudyal
M.Sc. MIT (12)
IOM, MMC
1
DOPPLER ULTRASOUND AND
ADVANCES IN USG
TECHNOLOGY

2. INTRODUCTION
 Doppler effect: Change in the perceived frequency of sound
emitted by a moving source.
 First described by Christian Doppler in 1843.
 Same effect that causes a siren on a fire truck to sound high
pitched as the truck approaches the listener (the wavelength
is compressed) and a shift to a lower pitch sound as it passes
by and continues on (the wavelength is expanded).
2

3.  In ultrasound, the Doppler effect used to measure blood
flow velocity.
 Ultrasound reflected from red blood cells will change in
frequency according to the blood flow velocity.
 When direction of blood flow is towards the transducer,
the echoes from blood reflected back to the transducer
will have a higher frequency than the one emitted from
the transducer.
 When the direction is away from the transducer, the
echoes will have a lower frequency than those emitted.
 The difference in frequency between transmitted and
received echoes is called the Doppler frequency shift,
and this shift in frequency is proportional to the blood flow
velocity.

4. 4

5. DOPPLER FREQUENCY SHIFT
 The Doppler shift is the difference between the incident
frequency and reflected frequency.
 When the reflector is moving directly away from or toward
the source of sound, the Doppler frequency shift (fd) is
calculated as
where fI is the frequency of the sound incident on the reflector
and fr is the frequency of the reflected sound.
 Thus, the Doppler shift is proportional to the velocity of
the blood cells.
5

6.  When the sound waves and blood cells are not
moving in parallel directions, the equation must be
modified to account for less Doppler shift.
 The angle between the direction of blood flow and
the direction of the sound is called the Doppler
angle.
 This reduces the frequency shift in proportion to the
cosine of this angle. If this angle is known then the
flow velocity can be calculated.
6

7. FACTORS AFFECTING DOPPLER SHIFT
1. Doppler angle
2. Transducer frequency
3. Scattering of US by blood
4. Blood flow characteristic

8. 1. DOPPLER ANGLE
 Also known as the angle of insonation.
 Estimated by a process known as angle correction,
which involves aligning an indicator on the duplex
image along the longitudinal axis of the vessel.
 Few considerations that affect the performance of a
Doppler examination:
 The cosine of 90° is zero, so if the ultrasound beam is
perpendicular to the direction of blood flow, there will be no
Doppler shift and it will appear as if there is no flow in the
vessel
 The angle of insonation should also be less than 60° at all
times, since the cosine function has a steeper curve above
this angle, and errors in angle correction will be magnified

9. ANGLE EFFECTS
 Maximum Doppler shift at 0 degrees minimum at 90
degrees – proportional to the Cosine of the angle
between the beam and direction of travel.
Direction of movement

10. Effect of the Doppler angle in the sonogram. Higher-frequency Doppler signal is
obtained if the beam is aligned more to the direction of flow. In the diagram, beam
(A) is more aligned than (B) and produces higher-frequency Doppler signals. The
beam/flow angle at (C) is almost 90° and there is a very poor Doppler signal. The
flow at (D) is away from the beam and there is a negative signal.

11. 11
If the beam direction is perpendicular to the
direction of flow, the Doppler frequency is ZERO!

12. 2. TRANSDUCER FREQUENCY
 Increase in transducer frequency causes increased
doppler frequency shift.
 At frequencies between 2-10 MHz, doppler shift
comparatively small & in audible range (shift from 0-
10 KHz) for most physiological motion (for velocity
range from 0-100 cm/s).
 Change of frequency → measurable → movement of
reflector towards/away from transducer.
 Depending on ↑ or ↓ in frequency → direction of
movement.

13. c
cosθv2f
F o
D 
13

14. 3. SCATTERING OF US BY BLOOD
 Smooth wall of blood vessel → specular reflection
→ strong echoes.
 Us wavelength > size of RBCs → scattering of
wave in all directions (Rayleigh-Tyndall scattering).
Size of echo from blood → ↓.
 Intensity of scattered us ↑ with 4th power of
frequency as images of vessel lumen differ
significantly with instruments of different frequency.

15. 4. CHARACTERISTICS OF BLOOD FLOW
 Blood (viscous medium) → wall exerts drag effect on
moving blood → slow movement near the wall than center.
 Non pulsatile flow with low velocity → parabolic velocity
profile → laminar flow.
 Fast /accelerated flow → same velocity all over → plug
flow.
 Major artery → plug flow during systole & laminar flow
during diastole. Venous flow → laminar.

16. FLOW PATTERNS
 Laminar flow
 Highest in center
 Zero at wall
 Turbulent flow
 Larger distribution of
velocities
16

17. BASIC EQUIPMENT
 Same probe can be used for Doppler Scanning.
 High Q transducer material (transducer will produce
narrow range of frequency)
 Air backing can be used for maximal sound
reflection from backing layer.
 Lower frequency probe. Usually 3.5MHZ probe.
17

18. TYPES OF DOPPLER OPERATION
1. Continuous wave doppler
2. Pulsed wave doppler
3. Duplex scanning
4. Color flow doppler imaging
5. Power doppler
18

19. 1. CONTINUOUS WAVE DOPPLER
 Simplest and least expensive device for measuring
blood velocity
 Two transducers required, one transmitting the incident
ultrasound and other detecting the resultant continuous
echoes.
 Two elements in one transducer at inclination.
 High Q transducer with no backing block
 Suffers from depth selectivity with accuracy affected by
object motion within the beam path.
 Multiple overlying vessels will result in superimposition,
making it difficult to distinguish a specific Doppler signal.
19

20. 20

21. Advantages:
 Simple, Good quality
 low noise signal,
 No aliasing.
Disadvantages:
 Lacks depth resolution,
 Confusing superimposition,
Application: Superficial structures,e.g carotid artery,
limb arteries.
21

22. 2. PULSED WAVE DOPPLER
 Combines the velocity determination of continuous wave
Doppler systems and the range discrimination of pulse-
echo imaging.
 Transducer is used in a pulse-echo format, similar to
imaging.
 The SPL is longer (a minimum of 5 cycles per pulse up to
25 cycles per pulse) to provide a higher Q factor and
improve the measurement accuracy of the frequency shift
(although at the expense of axial resolution).
 Depth selection is achieved with an electronic time gate
circuit to reject all echo signals except those falling within
the gate window, as determined by the operator.
22

23.  Each Doppler pulse does not contain enough
information to completely determine the Doppler
shift, but only a sample of the shifted frequencies
measured as a phase change.
 Stationary objects within the sample volume do not
generate a phase change in the returning echo
when compared to the oscillator phase, but a
moving object does.
 Repeated echoes from the active gate are analyzed
in the sample/hold circuit, and a Doppler signal is
gradually built up.
23

24. 24

25. 25

26.  Depth (range) controlled by time between pulse
transmission & gating on. Axial length ( thickness)
determined by time the gate is open.
 Width of sampling volume (gated Doppler acquisition
area) → width of Doppler beam (pear shaped).
 7 μs for ultrasound to travel 1 cm (average soft tissue)
 PRF determines the maxm. depth for Doppler shift. So
↑PRF → ↓depth.
 Doppler shift detection in pulsed Doppler = 1/2 of PRF.
 If Doppler shift frequency > detectable frequency in
deep vessels→ aliasing (incorrect shift).

27. 27

28.  The discrete measurements acquired at the PRF produce
the synthesized Doppler signal.
 According to Nyquist sampling theory, a signal can be
reconstructed unambiguously as long as the true frequency
(e.g., the Doppler shift) is less than half the sampling rate.
 Thus, the PRF must be at least twice the maximal Doppler
frequency shift encountered in the measurement.
 For Doppler shift frequencies exceeding one-half the PRF,
aliasing will occur, causing a potentially significant error in
the velocity estimation of the blood.
 Thus, a 1.6-kHz Doppler shift requires a minimum PRF of 2
*1.6 kHz =3.2 kHz.
 One cannot simply increase the PRF to arbitrarily high
values, because of echo transit time and possible echo
ambiguity.
28

29. Aliasing of the spectral Doppler display is characterized by "wraparound“
of the highest velocities to the opposite direction when the sampling (PRF)
is inadequate. Right: Without changing the overall velocity range, the
spectral baseline is shifted to incorporate higher forward velocity and less
reverse velocity to avoid aliasing. The maximum, average, and minimum
spectral Doppler display values allow quantitative determination of
clinically relevant information such as pulsatility index and resistive index.

30. Advantages:
 Identification of source.
 Small signal crystal transducer (cardiology).
 Blood flow signal from ranges gate
Disadvantages:
 Quality may suffer d/t background noise (switching).
 Aliasing.

31. 3. DUPLEX SCANNING
 Combination of 2D B-mode imaging and pulsed Doppler
data acquisition.
 Operates in the imaging mode and creates a real-time
image.
 The Doppler gate is positioned over the vessel of
interest with size (length and width) appropriate for
evaluation of blood velocity, and at an orientation (angle
with respect to the interrogating US beam) that
represents the Doppler angle.
 When switched to Doppler mode, the scanner
electronics determines the proper timing to extract data
only from within the user-defined gate.
31

32.  Most often, electronic array transducers switch
between a group of transducers used to create a B-
mode image and one or more transducers used for the
Doppler information.
 The duplex system allows estimation of the blood
velocity directly from the Doppler shift frequency, since
the velocity of sound and the transducer frequency are
known, while the Doppler angle can be estimated from
the B-mode image and input into the scanner computer
for calculation.
 Once the velocity is known, flow (in units of cm3/s) is
estimated as the product of the vessel’s cross-
sectional area (cm2) times the velocity (cm/s).
32

33.  Errors in the flow volume may occur. The vessel
axis might not lie totally within the scanned plane,
the vessel might be curved, or flow might be altered
from the perceived direction.
 The beam-vessel angle (Doppler angle) could be in
error, which is much more problematic for very
large angles, particularly those greater than 60
degrees
 The Doppler gate (sample area) could be
mispositioned or of inappropriate size, such that the
velocities are an overestimate (gate area too small)
or underestimate (gate area too large) of the
average velocity.
 Noncircular cross sections will cause errors in the
area estimate, and therefore errors in the flow
volume. 33

34.  Advantages:
 Selection of site & sample volume for Doppler.
 No overlap of information from other vessels/structures.
 Measurement of vessel angle in 2-3 sec.
 Disadvantages:
 Angle restriction if same transducer for imaging &
Doppler.
 Flow information from one site in image

35. 4. COLOUR DOPPLER FLOW IMAGING.
 Provides a 2D visual display of moving blood in the
vasculature which is superimposed on the conventional
gray scale image.
 Imaging of flow through entire real-time image.
 Allowing visualization of blood vessels and their flow
characteristics + image of tissue surrounding.
 Multiple gate in receiving transducer circuit each gate
is controlled by time delay circuit.
 These gate arrange close to each other so they can
simultaneously sample Doppler shift information across
entire lumen of large vessels.
 Multiple gate+ real time 35

36.  Velocities and directions are determined for multiple
positions within a subarea of the image, and then color
encoded (e.g., shades of red for blood moving toward
the transducer, and shades of blue for blood moving
away from the transducer).
36

37. Advantages:
 Vessels small on gray scale image can be seen (presence of flow
detected with relative ease)
 Differentiation between and other structure simplified.
 Improved definition of lumen.
 Improved measurement of stenosis.
Limitations:
 Compute mean velocity and image not corrected for doppler angle
so it is qualitative .
 PRF limited
 Detailed study of vessels not possible.
 May obscure vascular pathology due improper adjustment.
 Other motion like peristalsis, cardiac motion may represented as
color which may obscure signal.
 High cost.
 spatial resolution poorer than gray scale image, noise of slowly
moving structure can affect the small echoes returning from the
moving blood cell. 37

38. 5. POWER DOPPLER
 A signal processing method that relies on the total
strength of the Doppler signal (amplitude) and ignores
directional (phase) information.
 The power (also known as energy) mode of signal
acquisition is dependent on the amplitude of all Doppler
signals, regardless of the frequency shift.
 This dramatically improves the sensitivity to motion (e.g.,
slow blood flow) at the expense of directional and
quantitative flow information.
 Does not give the flow direction or the velocity, but is
more sensitive to detecting small amounts of flow, as
noise in the image is reduced.
 Aliasing artifacts do not occur in Power Doppler
 3-dimensional Power Doppler is also possible 38

39.  Power Doppler produces images that have more
sensitivity to motion and are not affected by the Doppler
angle (largely nondirectional),
 Aliasing is not a problem as only the strength of the
frequency shifted signals are analyzed (and not the
phase).
 Greater sensitivity allows detection and interpretation of
very subtle and slow blood flow.
 On the other hand, frame rates tend to be slower for the
power Doppler imaging mode, and a significant amount
of "flash artifacts" occur, which are related to color
signals arising from moving tissues, patient motion, or
transducer motion.
39

40. Color flow (top) and power Doppler (bottom)
images of the same phantom under the same conditions.
The directions of flow toward and away from
the transducer are seen in the color flow image (top).
The power Doppler image (bottom) displays only the
intensity of the Doppler shift

41. Advantages:
 No aliasing
 Angle independent
 Increased sensitivity to detect low- velocity flow
 Useful in imaging tortuous vessels
 Increases accuracy of grading stenosis
Disadvantages:
 Do not provide velocity of flow
 Donot provide direction of flow
 Very motion sensitive( poor temporal resoultion)
41

42. SPECTRAL ANALYSIS
 The Doppler signal is typically represented by a
spectrum of frequencies resulting from a range of
velocities contained within the sampling gate at a
specific point in time.
 With the pulsatile nature of blood flow, the spectral
characteristics vary with time.
 Interpretation of the frequency shifts and direction of
blood flow is accomplished with the fast Fourier
transform, which mathematically analyzes the detected
signals and generates amplitude versus frequency
distribution profile known as the Doppler spectrum

43.  The intensity of the Doppler signal at a particular
frequency and moment in time is displayed as the
brightness at that point on the display.
 Velocities in one direction are displayed as positive
values along the vertical axis, and velocities in the other
direction are displayed as negative values. As new data
arrive, the information is updated and scrolled from left
to right.

44. Pulsed-wave US spectrum displays the maximum, minimum,
and average calculated blood flow velocities. The pulsatility
index, resistivity index, and systolic-to-diastolic ratio are
calculated from these values

45. The PI will increase as flow is impeded by a stenosis. Care must be
taken when the PI is used. Proximal and distal stenoses as well as
natural flow resistance from the vascular bed may affect PI
measurement. The RI is easier to calculate and is used to evaluate
a number of physiologic conditions. Both of these indexes are used
to assess the resistance to flow in the vascular system

46. ADVANCEMENTS IN
USG TECHNOLOGY
46

47. HARMONIC IMAGING
 Harmonic frequencies are integral multiples of the frequencies
contained in an ultrasound pulse (a f MHz, upon interaction
with a medium, will contain high-frequency harmonics of 2f,3f,
4f and so on, etc.)
 These higher frequencies arise through the vibration of
encapsulated gas bubbles used as ultrasound contrast agents
or with the nonlinear propagation of the ultrasound as it travels
through tissues.
 Harmonic imaging enhances contrast agent imaging by using
a low-frequency incident pulse and tuning the receiver (using
a multi frequency transducer) to higher-frequency harmonics.
 For harmonic imaging, longer spatial pulse lengths are often
used to achieve a higher transducer Q factor.
 Improve the sensitivity to the ultrasound contrast agent.
47

48.  Body wall region close to transducer →less harmonics.
 At depth → less harmonics (increasing attenuation of
higher order harmonics). Strongest harmonics at greatest
pressure amplitudes (near pulse center).
 Resultant effect → at near surface good rejection of
artifacts & clutter from multiple pulse reflections.
 Most useful in technically difficult patients i. e. thick &
complicated body wall structures.
 Conventional imaging → hazy image (distortion of the
transmitted beam by shallow surface layers or to
reverberations between the skin and ribs). The
distortions and reverberations consist entirely of us
energy at the fundamental frequency.

49.  Peculiarities of harmonic image:
 Increase signal-to-noise ratio with better
interpretation of image.
 Superior lateral & elevational resolution as
compared to the fundamental images.
 Removal of clutter and haze with more clear and
defined image due to side-lobe level reduction in
the second harmonic beam. Harmonic beams are
narrower with lower side-lobe levels than
fundamental ones.

50. 51

51. EXTENDED FOV IMAGING
 The transducer is slowly translated laterally across
the large anatomic region of interest.
 During this motion, multiple images are acquired
from many transducer positions.
 The proper relative positions of the multiple images
are determined in the regions of overlap between
successive images.
 The registered image data are accumulated in a
large image buffer and then combined to form the
complete large FOV image
 Can be used to view whole course of vessels.
52

52. 53

53. CODED PULSE EXCITATION
 Short, highly focused ultrasound pulses that optimize spatial
resolution are generally obtained at higher frequencies.
 Higher frequency-more attenuation.
 Coded ultrasound pulses are a potential means of
overcoming this limitation, providing good penetration at the
higher frequencies necessary for high spatial resolution.
 The coded pulses are produced with a very specific,
characteristic shape, and the resulting echoes will have a
similar shape.
 These pulse shape locations may be determined with a tight
spatial tolerance and are assumed to correspond to the
locations of reflective structures in the body.
 The end result is an image with good echo signal and good
spatial resolution at large depths.
54

54. Conventional B-mode and coded pulse US images of the liver. The spatial
resolution of the coded pulse image is very comparable with that of the 13-MHz
conventional image . However, the useful imaging depth is about 7.5 cm for the
coded pulse image compared with only about 2.8 cm for the conventional image.

55. 3D US
 3D ultrasound imaging acquires 2D tomographic image data
in a series of individual B-scans of a volume of tissue.
 Forming the 3D dataset requires location of each individual
2D image using known acquisition geometries.
 3D ultrasound works by taking thousand of slices in a series
(called volume of echoes) the volume are then digitally
stored and shaded to produce 3D images that look more life
like.
56

56. 57
Volume sampling can be achieved in several ways with
a transducer array:
(1) linear translation,
(2) freeform motion with external localizers to a
reference position,
(3) rocking motion, and
(4) rotation of the scan

57. 4D ULTRASOUND
 4D Ultrasound represents the difference between video
and a still photograph.
 Through this technology, three-dimensional image is
continuously updated, providing a "live action" view.
 The entirely digital platform and very fast processors
cope with the large volume of data required to
reconstruct 3D images again and again, giving the
impression of a moving image.
 4D Ultrasound takes multiple 2-dimensional ultrasound
images, creates a 3-dimensional image and adds the
element of time to the process. The result: live action
images of any internal anatomy.
58

58. Chewing
Sleepy
Firstwhinge
Smiling
59

59. ELASTOGRAPHY
 Stiffness and compliance of different tissue can be
assessed .
 A set of digital RF echo data from ROI is obtained and
the tissue is then compressed usually by transducer and
further set of RF echo data obtained.
 This is then cross correlated with initial data and any
changes in arrival time of pulses from equivalent volume
of tissue can be obtained.
 An estimate of local tissue strain can be asssessed and
from this the degree of tissue stiffness can be assessed.
 Tissue stiffness is described by the Young modulus
expressed in kilopascals (E = 3γC2).
 The elastography methods are based on a common
approach: measurement of deformation induced in a
tissue by a force.
60

60.  Elastography is therefore an application, which
produces the force coupled with a measurement
system for the deformities caused by the force.
 There are several types of forces or applications:
 static compression induced externally by manual
compression or internally by organ motion (heart,
vessel, breathing);
 dynamic compression induced with a continuous
vibration at a given frequency;
 impulse compression (transient vibration): induced
externally by a transient mechanical impulse
(FibroScan®) or internally by an ultrasound impulse
(ARFI, SWE), both compression types producing shear
waves.
61

61. ELASTOGRAPHY TECHNIQUES
 Impulse elastography:
 Uses an external mechanical device (FibroScan) or an
internal acoustic radiation force (ARFI and SWE) to induce
shear waves in the tissue to be explored.
 Shear wave propagation velocity (Vs) is then measured in
m/s using ultrasound imaging in the tissue being studied in
order to assess its stiffness.
 Uni-dimensional transient elastography: FibroScan
 Developed around 10 years ago
 Based on shear wave, which is generated by an external
mechanical impulse and whose speed is measured by an
ultrasound one-dimensional probe.
 The one-dimensional probe (3.5 MHz) is mounted along the
axis of an electro-dynamic transducer (vibrator).
62

62. 63
• The FibroScan® estimates liver stiffness by measuring the
velocity of elastic shear waves in the liver parenchyma
generated by the mechanical push.
• The propagation velocity is directly related to the stiffness of the
medium, defined by the Young modulus.
• Stiff tissues exhibit higher shear wave velocities than soft
tissues.

63.  Acoustic Radiation Force Impulse (ARFI) Imaging
mode elastography:
 A new method for quantifying mechanical properties of tissue,
without manual compression, by measuring the shear wave
velocity induced by acoustic radiation and propagating in the
tissue.
 Developed by Siemens.
 Provides a single uni-dimensional measurement of tissue
elasticity like the FibroScan, although the measurement area
can be positioned on a two-dimensional Bmode image.
 The region is a 1 × 0.5 cm rectangular, which can be freely
moved in the two-dimensional Bmode image to a maximum
depth of 8 cm from the skin plane.
 The measurement is expressed in m/s, expressing shear
wave speed, travelling perpendicular to the shear wave
source.
 The technique has been implemented on the ultrasound
probe designed for abdominal imaging.
64

64. 65

65.  Shear Wave Elastography (SWE):
 Was introduced in 2005.
 Relies on the measurement of the shear wave propagation
speed in soft tissue; like ARFI, does not require an
external vibrator to generate the shear wave. Based on the
generation of a radiation force in the tissue to create the
shear wave.
 The ultrasound probe produces a very localized radiation
force deep in the tissue of interest that induces a shear
wave, which then propagates from this focal point.
 Several focal points are then generated almost
simultaneously, in a line perpendicular to the surface of the
patient's skin.
 This creates a conical shear wave front, which sweeps the
image plane, on both sides of the focal point. The
progression of the shear wave is captured by the very
rapid acquisition of ultrasound images (up to 20,000
images per second), called UltraFast Imaging.
66

66. 67
 A high-speed acquisition is necessary to capture the shear wave as it
moves at a speed in the order of 1 to 10 m/s.
 Comparison of two consecutive ultrasound images allows the
measurement of displacements induced by the shear wave and creates
a “movie” showing the propagation of the shear wave whose local speed
is intrinsically linked to elasticity.
 The propagation speed of the shear wave is then estimated from the
movie that is created and a two-dimensional color map is displayed, for
which each color codes either the shear wave speed in meters per
second (m/s), or the elasticity of the medium in kilopascals (kPa).
 This color map is accompanied by an anatomic reference gray scale (or
B-mode) image. This quantitative imaging technique is a real-time
imaging mode.

67.  Static elastography:
 Developed by Hitachi.
 The operator manually applies gentle pressure with the
ultrasound probe in order to induce in the underlying tissues a
deformation.
 Only the deformed tissue subject to the manual compression is
measured, rather than a direct measurement of elasticity. The
deformation is considered to be inversely proportional to elasticity.
 A color map of tissue elasticity is obtained: this is a qualitative
approach. In more recent systems, the deformation of the liver
parenchyma as a result of vascular beating or respiration alone
has also been used.
68

68. TRANSDUCER DEVELOPMENTS
69
 Multielement array transducers:
 Possible for US beam focus and stear electronically,
different group of elements can be used for different
tasks e.g pulse doppler.
 Beam can be manipulated in two direction thus
improving resolution.
 Now days 2D array are available possible for volume
scan(3D and 4D possible)

69.  Small sized transducers:
 Can be mounted on catheter to pass into coronary
arteries.
 Specialized transducer like trans rectal and TVS(endo
cavitary).
70

70. ECHO-ENHANCING AGENT
 Most agents comprised of encapsulated microbubbles of
3 to 5 micrometer diameter containing air, nitrogen, or
insoluble gaseous compounds such as
perfluorocarbons.
 Encapsulation materials, such as human albumin,
provide a container for the gas to maintain stability for a
reasonable time in the vasculature after injection.
 Response of US to microbubble depends on acoustic
power.
 At low power (MI -0.1-0.3) they reflect and scatter Us.
 At moderate power (MI abt 0.5) they resonate frequency of
US.
 At high power (MI-0.7-0.8) microbubble oscillate nonlinear
fashion and production of harmonic signal which are specific
to agent .
 More than this power micro bubble disrupted and brust.
71

71. SPATIAL COMPOUND IMAGING
 Aims to improve image quality by averaging several
coplanar ultrasound frames into a single image.
 Mechanism:
 Repeated us beam steering in same tissue by an
array transducer using parallel beams oriented in
different directions→ echoes from multiple
aquisition of same tissue → averaged → single
composite image.
 Multiple beams for same tissue (vs one beam in
conventional B-mode imaging) hence more time for
data acquisition & reduced frame rate.

72. set of us beam lines for conventional imaging
Two additional set of us beam lines for spatial compound imaging. Upto nine sets
are used.

73.  Advantages of compound imaging:
 greater spatial details of lesions and tissue in the FOV
with decreased image graininess (due to speckle).
Speckle varies with beam line direction, averaging
echoes from different directions average out and
smooth the speckle with less grainy image.
 Improved contrast & margin definition.
 Reduction of enhancement & shadowing artifacts.
Conventional image of breast mass Spatial compound imaging of breast
mass

74. ELECTRONIC SECTION FOCUSING
 Electronic focusing of US pulse in the lateral direction by transducer
arrays produces great benefits compared with mechanical focusing.
 Most transducers in current clinical use still employ mechanical
focusing (curved piezoelectric elements or acoustic lenses) in section
thickness direction → resultant highly variable section thickness →
great difficulty in accurately visualizing small structures.
 Electronic focusing is employed with more than one-dimensional
single row of piezoelectric elements {referred to as 1.25D, 1.5D,
1.75D, or full 2D (two-dimensional) arrays} as per the number of
element rows and the level of independence with which the individual
rows may be excited.
 Full-size, filled 2D array transducers are not yet commercially
available, only 1.25D arrays are available.
 The greater the number of rows, the greater the ability for full
electronic focusing which provide multiple, user-selectable elevational
focusing and more uniform section profiles.

75. US images of a phantom with small anechoic spheres in conventional B mode &
electronic focusing in section thickness direction.

76. MINIATURIZATION
 Modern full-size US scanners are relatively portable
and inexpensive.
 The general trend toward hardware miniaturization
and the use of dedicated integrated circuitry is
making possible even smaller and less expensive
US scanners, with few (if any) compromises in
general image quality and available features.
 This trend toward lower cost and smaller systems
has great potential to radically alter the overall role
of US in medicine.

77. Commercially available small US scanners from two vendors. The left scanners
are 13.3 in (33.8 cm) tall and weigh 5.7 lb (2.6 kg), whereas the right scanners
weigh about 3 lb (1.4 kg). The dedicated electronics module attached to the
transducer cable weighs 10 oz (0.3 kg) and is 7.6 in (19.3 cm) long.

78. FUSION TECHNOLOGY
 An emerging technique in the field of abdominal imaging with
translation possibilities to neuroradiology.
 Involves co-registered display of live ultrasound with a
reference series from another modality, such as CT, MRI or
PET.
 As the ultrasound exam is performed the fusion system
continuously generates reformatted planes from the reference
series matching the oblique imaging planes of the ultrasound
transducer.
 The reformatted planes are displayed either as an overlay or
side-by-side with the live ultrasound.
 This display enhances interpretation of ultrasound by enabling
a direct comparison with the reference images from the same
view angle.
79

79.  Fusion imaging makes use of a tracking system to
localize ultrasound transducers and other devices
relative to the patient.
 Optical and electromagnetic systems are available,
the latter being most commonly used.
 Various software tools are also used to bring the
reference series into alignment with the tracking
system for fusion display.
 Tracking sensors are also incorporated into some
interventional devices such as introducers and
ablation needles, enabling the display of needle
location as an overlay on live ultrasound image.
 For the fusion imaging technique, a variety of
tracking methods are available, including optical,
image-based, and EM tracking.
80

80. 81
Fusion imaging and contrast-
enhanced ultrasonography (US)-
guided radiofrequency ablation
(RFA) of a 1-cm hepatocellular
carcinoma (HCC) in a patient with
a hepatitis B virus carrier

81. 82

82. WIRELESS TRANSDUCER
 They feature proprietary ultra-wideband (UWB) wireless
radio to help ensure images are transferred at high
speeds, with full data integrity and free from interfering
with other medical equipment—and
all without cables.
 These breakthrough cable-free innovations help provide
uninterrupted, hassle-free, real-time imaging that allows
you to scan in the position that is comfortable for you
and safe for your patient.
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83. SMARTPHONE ULTRASOUND
 Inexpensive, which will lead to even
wider use, especially in rural and
third-world areas
 Widespread use in Emergency
Rooms, and in the surgical and
medical wards, as well as in office
practice
 A great start for diagnosing all types
of medical problems, as a screening
device, such as vascular problems,
gallstones, kidney stones, abdominal
masses, and other problems.
 The model shown is a
Mobisante which is the world’s first
smartphone-based ultrasound
imaging system, the MobiUS SP1
ultrasound system. 84

84. CONCLUSIONS
 Modern US equipments are based on many of the
same fundamental principles employed in the initial
devices used for human imaging over 50 years ago.
 USG is relatively inexpensive, portable, safe, and
real-time in nature, all of which make it one of the
most widely used imaging modalities in medicine.
 B-mode US continues to experience very significant
evolution in capability with the US science,
technology, and applications are expanding at a
brisk pace and are far from mature with exciting
developments in future.

85. FIND MORE AT:
 The essential physics of medical imaging;
Bushberg JT, Seibert JA et.al.
 AAPM/RSNA Physics Tutorial for Residents: Topics
in US
 Ultrasound elastography in liver; Frulio N, Trilaud H.
 Fusion imaging of real-time ultrasonography with
CT or MRI; Lee MW
 http://e-ultrasonography.com
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86. 87