An easy guide for Instrumental Physics and Medical Imaging regarding Basics of Ultrasound Physics

1. Nouman Ahmed
MIT FMH CM&D

2.  Ultrasound or ultrasonography is a medical
imaging technique that uses high frequency
sound waves and their echoes.
 Known as a ‘pulse echo technique’
 The technique is similar to the echolocation
used by bats, whales and dolphins, as well as
SONAR used by submarines etc.

3. 1. The ultrasound machine transmits high-frequency (1 to
12 megahertz) sound pulses into the body using a
probe.
2. The sound waves travel into the body and hit a
boundary between tissues (e.g. between fluid and soft
tissue, soft tissue and bone).
3. Some of the sound waves reflect back to the probe,
while some travel on further until they reach another
boundary and then reflect back to the probe .
4. The reflected waves are detected by the probe and
relayed to the machine.

4. 5. The machine calculates the distance from the
probe to the tissue or organ (boundaries) using the
speed of sound in tissue (1540 m/s) and the time
of the each echo's return (usually on the order of
millionths of a second).
6. The machine displays the distances and
intensities of the echoes on the screen, forming a
two dimensional image.

5.  All the energy comes from the transducer
 All we “see” are reflections and scatter.

6. •Sound waves consist of mechanical vibrations containing
condensations (compressions) & rarefactions
(decompressions)that are transmitted through a medium.
•Sound is mechanical.
•Sound is not electromagnetic.
•Matter must be present for sound to travel

8. •Infrasound (subsonic) below 20Hz
•Audible sound 20-20,000Hz
•Ultrasound above 20,000Hz
•Non-diagnostic medical applications
<1MHz
•Medical diagnostic ultrasound >1MHz

9.  Produces electrical Voltage bursts that are sent
to the transducer.
 Sends upto 10,000 voltage bursts per second
 RVPM(rapid voltage pulse system

10.  Piezo-electric crystal
Converts electric signals to mechanical &
vice versa
 Transmits pulses of sound into tissue and
listens for echos
 Most of the time is spent listening for
echoes

11.  Receives echo signal and amplifies it to read
through machine

12.  Puts image data together.
 Each retuning data is read in the form of pixel
or grain mode.
 Signal received is stored in the memory
allocation known as “pigeon hole”
 Receiver signal is evaluated for two reasons.
 Time(location)
 Strength(brightnes)

13.  All bits of data is accumulated until a complete
image is formed.
 When its done, it is then sent to display on
monitor.
 Strong echoes are seen as bright spots
 Mid level echoes as gray
 Weak or no echoes as black spots on the
image

15.  Used to obtain a permanent record of scan
 Different recoding devices can be used
 Film or digital cameras
 Videos
 Optical discs
 Digital data drives
 PACS

16. Transducer Power on Power off
Transducer receiving
echoes10-6
sec
10-3
sec

18.  A mechanical process that is caused by vibration
phenomena.
 Adjacent formal particles hit later particles and
propagate or transfer their energy to other
 unit=frequency (Hz)
 number of waves repetition in one second.
 Infrasounds (below audible range i.e. <20kHz)
 Audible sounds(with in human range 20-20kHz)
 Ultrasound (above 20,000Hz)

19.  Waves on the surface of water
 Contraction waves in myometrium
 Crowd waves
 Radio Waves
As a sonographer you should know:
 Longitudinal waves
 Transverse waves

20.  Displacement of Particles is 90 degree
perpendicular to the direction of wave travel.
 Electromagnetic radiation travel as tranverse
waves.

21.  Particle Displacement is parallel to the
propagation of wave.
 Sound is a longitudinal wave.

22.  Mechanical Wave
 Longitudinal Wave
 Pressure Wave
 Form of Energy
 Converge and Diverge
 Reflect
 Non-Ionizing
 Not an electromagnetic wave.

23.  Waves carry energy from one point to another.
 Acoustic Variables show the measurable
characteristics of a medium of propagation.
 Acoustic Variables are:
 Pressure
 Density
 Particle Motion
 Temperature

24.  Pressure:
 Amount of force in a given area.
 Unit:
 Pascal (Pa)
 Pounds per square inch(lbs/in sq)
 Newton per square meter(N/m sq)
 Density:
 Mass per unit volume.
 Unit:
 Kilogram per cubic meter (kg/m3)
 Gram per cubic centimeter (g/cm3)

25.  Temperature:
 Concentration of heat energy.
 Unit
 Fahrenheit
 Celsius
 Kelvin
 Particle Motion:
 Distance moved by particles in a medium

26. Amplitude
Compression
Rarefaction

27.  Compression:
 High Density or peak where particles lie in
abundance point
 Relaxation(rarefaction):
 Areas where pressure density is low
 Amplitude:
 Strength of a wave
 In sound, it is called loudness.

28.  Number of events occurring in a specific
duration of time.
 Number of Acoustic Variable Cycles that occur
in one second.
 Number of Vibrations per second.
 Units:
 Hertz
 Cycles per second

29.  General Abdomen 2 – 5
 Gallbladder 3 – 5
 Ob/Gyne 3 – 3.5
 Adult Heart 2 – 3
 Pedriatic Heart 3 – 5
 Neck, Breast, Scrotum 5 – 15
 Eye 7 – 15
 Endoluminal Ultrasound 15 – 30
Frequency is
directly proportional
to Resolution and
Inversely
Proportional to
Penetration

30.  Distance over which one complete wave cycle
occurs.
 Distance between any two consecutive points.

31.  Wavelength is directly proportional to speed of
sound and inversely proportional to the
frequency.
 By using the speed of in sift tissue (1540m/s or 1.54
mm/µs) we can determine the wavelength of different
tissues at different frequencies.
Wavelength =
Speed of sound
Frequency