Welcome to the presentation on the Physical Principles of Ultrasound. Today, we will discuss the fundamental principles underlying medical ultrasound imaging, a crucial tool in radiology. Sound waves with frequencies higher than the upper audible limit of human hearing are called ultrasound. 

1. Physical Principle of
Ultrasound
Presenter: Dr. Dheeraj Kumar
MRIT, Ph.D. (Radiology and Imaging)
Assistant Professor
Medical Radiology and Imaging Technology
School of Health Sciences, CSJM University, Kanpur

2. Introduction
• Welcome to the presentation on the Physical Principles of Ultrasound.
Today, we will discuss the fundamental principles underlying medical
ultrasound imaging, a crucial tool in radiology. Sound waves with
frequencies higher than the upper audible limit of human hearing are
called ultrasound.
• The limit varies from person to person but is approximately 20,000 Hertz. The
physical properties of ultrasound are similar to the normal audible sound.
Monday, 16 October 2023 Physical Principle of Ultrasound By- Dr. Dheeraj Kumar 2

3. • Significance: Understanding these principles is essential for radiology
professionals as it forms the basis for image formation and
interpretation.
• Agenda: We will explore ultrasound waves, their generation, the
piezoelectric effect, transmission through tissues, reception, and
imaging modes.
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4. Ultrasound Waves
• Ultrasound Waves:
Ultrasound is a high-frequency
sound wave beyond the range
of human hearing (>20,000
Hz). In medical imaging,
frequencies typically range
from 2 to 18 MHz.
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5. • Properties: Ultrasound waves have
properties such as frequency (number of
cycles per second), wavelength (distance
between two wave cycles), and speed
(typically 1540 m/s in soft tissues).
• Inaudible Sound: These waves are
inaudible to the human ear, making them
safe for diagnostic purposes.
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6. Ultrasound Frequency
Definition: Ultrasound frequency refers to the number of
sound waves or cycles that pass through a point in one second.
It is typically measured in Hertz (Hz) and falls within the
range of sound frequencies beyond the upper limit of human
hearing, typically above 20,000 Hz.
• Example: Medical ultrasound imaging commonly uses
frequencies in the range of 2 to 18 megahertz (MHz). For
instance, a medical ultrasound machine operating at 5 MHz
emits 5 million sound waves per second.
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7. Amplitude
Definition: Amplitude in ultrasound refers to the maximum
displacement of particles in a medium from their equilibrium
position as a sound wave passes through. It indicates the
strength or intensity of the ultrasound wave. A higher amplitude
corresponds to a more powerful wave, while a lower amplitude
indicates a weaker wave.
• Example: In medical ultrasound, the amplitude of the sound
wave determines the brightness of the images produced.
Higher amplitude waves may be used to visualize structures
with greater detail, such as when assessing the heart's valves
and chambers, while lower amplitude waves are suitable for
imaging soft tissues like the liver or kidneys.
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8. Wavelength
Definition: Wavelength in ultrasound refers to the distance
between two successive points that are in phase, meaning they
are at the same point in their respective cycles. It is inversely
related to frequency, meaning higher frequencies have shorter
wavelengths and vice versa.
• Example: If an ultrasound system emits waves at a frequency
of 10 MHz, the corresponding wavelength in soft tissue will
be approximately 0.15 millimeters. Shorter wavelengths are
advantageous for high-resolution imaging because they can
detect smaller structures, while longer wavelengths are better
for deeper penetration, as they suffer less attenuation.
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9. Relationship
The relationship between velocity (v), frequency (f), and wavelength (λ) in medical
ultrasound can be expressed using the following formula:
v = f x λ
Where:
• v represents the velocity of sound in the medium (typically soft tissue in medical
ultrasound, approximately 1540 m/s).
• f is the frequency of the ultrasound wave.
• λ is the wavelength of the ultrasound wave.
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10. Tissue Type Ultrasound Velocity (m/s)
Soft Tissue (Muscle) 1540 m/s
Adipose (Fat) Tissue 1450 m/s
Blood 1570 m/s
Bone (Cortical) 4080 m/s
Bone (Trabecular) 3080 m/s
Brain 1540 m/s
Liver 1550 m/s
Kidney 1560 m/s
Lung 480 m/s
Water 1480 m/s
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11. Generation of Ultrasound
• Generation: Ultrasound waves are generated
using a transducer. A transducer is a critical
component in an ultrasound machine, and it
operates based on the piezoelectric effect.
• Transducer: The transducer contains
piezoelectric crystals that convert electrical
energy into mechanical vibrations.
• Vibration: When an electrical current is
applied, the crystals vibrate, generating
ultrasound waves that travel into the patient's
body.
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12. (A) An ultrasound wave is depicted as a sine wave, propagating through tissue. Its wavelength depends on frequency,
inversely related to it. Amplitude measures the energy or pressure change in the wave, influencing loudness (amplitude) and
pitch (frequency). (B) Frequency determines pitch, while amplitude represents loudness in sound waves.
(C) Pulse length is inversely related to transducer frequency, with higher frequencies producing shorter pulses. These pulses
are emitted at a specific rate known as pulse repetition frequency.
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13. Piezoelectric Effect
• Piezoelectric Effect: This effect is central to
ultrasound technology. It refers to the ability of
certain materials (e.g., quartz, PZT) to generate an
electric charge when subjected to mechanical
stress.
• Two-Way Process: The piezoelectric effect is a
two-way process. It generates mechanical
vibrations when an electric current is applied (for
ultrasound transmission) and generates electrical
signals when mechanical vibrations are received
(for ultrasound reception).
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14. Ultrasound Transmission
• Transmission Through Tissues: Ultrasound waves travel
through the body, encountering different tissues. They can
be transmitted, reflected, refracted, and scattered.
• Refraction: When ultrasound waves change direction as
they pass through tissues with varying acoustic properties.
• Reflection: When waves bounce back at tissue boundaries
(e.g., bone-soft tissue interface), leading to echo formation.
• Scattering: Random redirection of waves due to small
structures within tissues.
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15. Ultrasound Reception
• Receiving Ultrasound Echoes: The same transducer used for transmission
also receives echoes. Here's how it works:
• When ultrasound waves encounter tissues, some are reflected back.
• These returning waves cause mechanical vibrations in the transducer's piezoelectric
crystals.
• These mechanical vibrations are then converted into electrical signals.
• Echo Formation: The time it takes for the ultrasound waves to return and
the amplitude of the returning waves are used to form an image.
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16. Ultrasound Imaging Modes
• Imaging Modes: Ultrasound can produce various imaging modes, each
with a specific clinical application.
• B-Mode (Brightness Mode): This is the most common mode, providing a
2D cross-sectional image of tissues. It relies on the intensity of returning
echoes to create brightness variations.
• Doppler Mode: Used to assess blood flow by detecting frequency shifts in
echoes caused by moving blood cells.
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17. Monday, 16 October 2023 Physical Principle of Ultrasound By- Dr. Dheeraj Kumar 17

18. • M-Mode (Motion Mode): This mode displays
motion over time, suitable for cardiac imaging.
• Color Doppler: Combines color and Doppler
modes to visualize blood flow direction and
velocity.
• 3D and 4D Imaging: Advanced techniques
that offer three-dimensional and real-time
images of structures, enhancing diagnostic
capabilities.
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19. Advantages of Ultrasound
Understanding the physical principles of ultrasound helps us appreciate its numerous advantages in
medical imaging.
• Non-Invasive: Ultrasound is non-invasive, avoiding the use of ionizing radiation.
• Real-Time Imaging: It provides real-time imaging, making it suitable for dynamic processes.
• High Spatial Resolution: Ultrasound has excellent spatial resolution, enabling fine detail
visualization.
• Safe for All Ages: It is safe for patients of all ages, including pregnant women and infants.
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20. Limitations
Despite its advantages, ultrasound has some limitations:
• Depth Limitations: Limited depth penetration in obese patients or when imaging deep structures.
• Sound Attenuation: Ultrasound waves weaken as they travel through tissues, potentially leading
to reduced image quality at greater depths.
• Artifacts: Ultrasound images can have artifacts like shadowing, reverberation, and refraction
artifacts.
• Operator-Dependent: Image quality can vary based on the operator's skill.
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21. Conclusion
In conclusion, understanding the physical principles of ultrasound is
vital for radiology professionals. It forms the foundation of medical
ultrasound imaging and is central to providing safe, high-quality patient
care.
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22. References
1. Kremkau, F. W. (2015). Sonography: Introduction to Normal Structure and Function. Saunders.
2. Hagen-Ansert, S. (2019). Textbook of Diagnostic Sonography: 2-Volume Set. Mosby.
3. Rumack, C. M., Wilson, S. R., & Charboneau, J. W. (2017). Diagnostic Ultrasound. Elsevier.
4. Oelze, M. L. (2008). Introduction to Infrasound: Piezoelectric Sensors. CRC Press.
5. Sauerbrey, G. (1959). Use of quartz vibration in microbalance studies. Journal of Physics and Chemistry of
Solids, 4(2), 206-212.
6. Stuart, D. A., Yuen, J. M., & Lyandres, O. (2008). In vivo nanoimaging of membrane-associated
biomolecules. Accounts of Chemical Research, 41(12), 1722-1731.
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23. Thank You
Monday, 16 October 2023 Physical Principle of Ultrasound By- Dr. Dheeraj Kumar 23