Its is useful for studying the basic concepts of ultrasound for medical imaging, very helpful for interns and sonographers

Its is useful for studying the basic concepts of ultrasound for medical imaging, very helpful for interns and sonographers

1. Introduction
Chandana.R
Dept. of MIT

2. Contents
•Principles of Sound
•Types of Sound
•Transducer Frequencies
•Continuous Wave, Pulsed
•Ultrasound Terminology, Amplitude, Intensity,
Propagation Speed -Density and Stiffness

3. WHAT IS SOUND...
•Sound is a vibration that typically propagates
as an audible wave of pressure, through a
transmission medium such as a gas, liquid or
solid.
•Humans can hear sound waves with
frequencies between about 20 Hz to 20 kHz.
•Sound above 20 kHz is ultrasound and below
20 Hz is infrasound. Animals have different
hearing ranges.

4. ULTRASOUND WAVES
•Acoustic waves are mechanical pressure waves
•Ultrasound waves are pressure waves that travel through a
medium at a frequency greater than 20 kHz .
Humans
•Can typically hear frequencies between 20 Hz to 20 kHz
•Children can detect higher frequencies than adults
Animals
•Bats use a variety of ultrasonic ranging (echolocation)
techniques to detect their prey. They can detect frequencies
beyond 100 kHz, possibly up to 200 kHz

5. Principles of Sound
•Medical ultrasound is based on the use of high-frequency sound
to aid in the diagnosis and treatment of patients. Ultrasound
frequencies range from 2 to approximately 15 MHz, although even
higher frequencies may be used in some situations.
•The ultrasound beam originates from mechanical oscillations of
numerous crystals in a transducer, which is excited by electrical
pulses (piezoelectric effect). The transducer converts one type of
energy into another (electrical <--> mechanical/sound).

6. •The ultrasound waves (pulses of sound) are sent from the
transducer, propagate through different tissues, and then return to
the transducer as reflected echoes. The returned echoes are
converted back into electrical impulses by the transducer crystals
and are further processed to form the ultrasound image presented
on the screen.
•Ultrasound transducers contain a range of ultrasound frequencies,
termed bandwidth. For example, 2.5-3.5 MHz for general
abdominal imaging and 5.0-7.5 MHz for superficial imaging.

7. •Ultrasound waves are reflected at the surfaces between the
tissues of different density, the reflection being proportional to the
difference in impedance. If the difference in density is increased,
the proportion of reflected sound is increased, and the proportion
of transmitted sound is proportionately decreased.
•If the difference in tissue density is very different, then the sound is
completely reflected, resulting in total acoustic shadowing.
Acoustic shadowing is present behind bones, calculi (stones in
kidneys, gallbladder, etc.) and air (intestinal gas)
(See Fig. 1 with acoustic shadowing).
•Echoes are not produced if there is no difference in a tissue or
between tissues. Homogenous fluids like blood, bile, urine,
contents of simple cysts, ascites and pleural effusion are seen as
echo-free structures.

8. Types of Ultrasound
1. 2D Ultrasound
•It is the traditional ultrasound scanning. It means the probe sends and
receives ultrasound frequency waves in one plane. Waves which are
reflected back are black-and-white images in a flat plane.

9. 2. 3D Ultrasound
•More advanced development of imaging technology has promoted
volume data or differing two-dimensional images which are
created by reflected waves at angles which differ from one
another. High-speed computing software then integrates this
information to create a 3D image.

10. •3D ultrasound advantages over the conventional 2D ultrasound machines
such as:
=> Virtual planes enable enhanced visualization of fetal heart structures.
=> Better diagnosis of fetal face, skeletal and neural tube defects.
=> This technology helps to identify structural congenital anomalies in the 18-20
week scan.
=> Reduced time for standard plane visualization.
=> Less dependence on operator’s experience and skill for diagnosing fetal
anomalies.
=> Recorded data is available for remote viewing.

11. 3. 4D Ultrasound
•This ultrasound technology enables live streaming of 3D
images. In other words, patients can view the live motion
of the fetal valves, heart wall blood flow, etc. 4D
ultrasound technology is 3D ultrasound in motion. A
3D transducer is utilized.

12. Advantages of using 4D ultrasound include:
•Shorter duration required for fetal heart screening/diagnosis
•Volume data storage capability for expert review, screening,
remote diagnosis, and teaching
•Enhances parental bonding with unborn baby
•Promotes healthier behavior as a result of viewing the baby
in real time
•Better identification of fetal anomalies

13. 4. 5D Ultrasound
•Currently, Samsung is the main player in the 5D ultrasound
technology arena. Their ultrasound portfolio includes the
Samsung WS80A Elite.
•2D ultrasound captures axial images, whereas 3D relies on
volume. 4D images combine volume and time while 5D attempts
to bring a new level of workflow, which borders on automation.
Samsung entered the ultrasound arena after considering which
exams are very time-consuming.

14. 5. Doppler Ultrasound
•Whenever there is relative
motion between a sound
source and a listener the
frequency heard by the
listener differs from that
produced by the source

15. Doppler equipment is commonly used for evaluating &
detecting blood flow in arteries and veins
Transducer is placed externally on the skin beam is
directed towards the vessel
Beam is at an angle θwith respect to the axis of the
vessel
RBC flowing in the vessel scatter us waves giving rise to
echo signal –detected by the same transducer

16. Clinical application:
•We use this principle to see how fast the
blood cells are moving.

17. TYPES
1. Continues wave doppler
2. Pulse doppler
3. Dupplex Scanner
4. Power doppler
5. Color doppler

18. CONTINUOUS WAVE
DOPPLER

19. CW
TRANSMITTER
TRANSDUCER
AMPLIFIER
DEMODULATOR
WALL FILTER
SPEAKER

21. CW doppler transducer

22. Advantages
•Detection of high flow velocities
•Inexpensive
Narrow spectrum - high measurement accuracy
•No aliasing artifact

23. Disadvantages
• Lack of depth discrimination
•Errors due to motion within path of
Continuous Wave US beam

24. Applications
•Superficial structures (carotid, vessels
in limb).
•Used for arteries with in the eye ,
female breast
•Obstetrics - To detect fetal heart motion

25. pulse DOPPLER

26. ❑ velocity and position.
❑One transducer element is
used.
❑Newer pulse is not
transmitted until the echoes
from previous is received.
PULSE DOPPLER:

27. ❑ A sample volume or depth gate is used to obtain
flow information from a selected depth.
❑ After transmission receiving transducer is turned
on (Gate On) for short period.
❑ Operator controls the depth by selecting the time
of the system.
PULSE DOPPLER:

28. Fig: Pulsed Doppler Instrumentation.

29. PULSED WAVE DOPPLER OF LIPV:

30. ADVANTAGES: DISADVANTAGES:
Precise depth at which flow is detected can
be specified.
Does not provide the information about
the structure
Flow information from a small portion of a
vessel can be isolated and analyzed without
interference from flow in adjacent areas.
Does not provide the site of origin of an
echo.
ADVANTAGES & DISADVANTAGES OF PULSE DOPPLER:

31. ❑ Performed by coupling the
ultrasound and pulse Doppler.
❑Real time Ultrasound image is
obtained and the image is frozen
then the Doppler mode is
switched on.
DUPLEX SCANNER:

32. ❑ Operator positions the location &axial length from which the
Doppler signal will be obtained by, locating the appropriate
cursor on the frozen image.
❑ Clinical applications of this concept may be difficult, because
arteries are not always nice and straight, and blood flow may
not be exactly parallel to the wall of the vessel.
DUPLEX SCANNER:

33. COLOUR DOPPLER Vs POWER DOPPLER:

34. Transducer Frequencies
•Ultrasound frequencies in diagnostic radiology range from
2 MHz to approximately 15 MHz.
•It is important to remember that higher frequencies of
ultrasound have shorter wavelengths and are
absorbed/attenuated more easily. Therefore, higher
frequencies are not as penetrating. This explains why
high frequencies are used for the superficial body
structures and low frequencies are used for those that are
deeper.

35. Medical ultrasound transducers contain more than one operating
frequency. The following frequencies are a guide to frequencies typically
used for ultrasound examination:
•2.5 MHz: deep abdomen, obstetric and gynecological imaging
•3.5 MHz: general abdomen, obstetric and gynecological imaging
•5.0 MHz: vascular, breast, pelvic imaging
•7.5 MHz: breast, thyroid
•10.0 MHz: breast, thyroid, superficial veins, superficial masses,
musculoskeletal imaging.
•15.0 MHz: superficial structures, musculoskeletal imaging.

37. AMPLITUDE
•The amplitude of an ultrasound pulse is the range of
pressure excursions, related to the energy content.
•In diagnostic applications it is necessarily to know only the
relative amplitude of ultrasound pulse.
•Unit is decibels(dB )
Ultrasound Terminology

38. WAVELENGTH AND FREQUENCY
WAVEVLENGTH
•The length of one period of the wave; e.g. from one
pressure peak to the next. The wavelength depends on
the frequency and the medium in which the sound wave
propagates.
FREQUENCY
•The frequency of the sound wave is the number of
oscillations per unit of time.
•Unit of cycles/s (Hz)

39. INTENSITY
•Intensity of sound is determined by the length of oscillation
(movement back and forth in a regular rhythm) of particles
conducting the waves
•Greater the amplitude of the oscillation, the more intense the
sound.
• RELATIVE SOUND INTENSITY: Sound intensity measured in
decibels { dB }

40. Reflection : it’s a phenomenon of propagating wave
(light/sound) being reflect back from its surface .
Refraction : the change in direction of wave due to a
change in its transmitted medium .
Acoustic impedance : it’s the product of density and
velocity minimize the acoustic impedance difference
between patient and transducer . Acoustic coupling gel
used .

41. Propagation Speed - Density and Stiffness
•The propagation speed of sound waves through tissue is
an important element of ultrasound scans. Ultrasound
machines assume sound waves travel at a speed of 1540
m/sec through tissue. In reality, the speed of sound is
affected by the density and elasticity of the medium
through which it is traveling and these factors are not
constant for human tissues. The propagation speed of
sound is higher in tissues with increased stiffness and
reduced density.

42. Examples of propagation velocities in different tissues are
given below :
•Air: 330 m/sec
•Fat: 1450 m/sec
•Water: 1480 m/sec
•Liver: 1550 m/sec
•Kidney: 1560 m/sec
•Blood: 1570 m/sec
•Muscle: 1580 m/sec
•Bone: 4080 m/sec

43. Thank You