Ultrasonography, or ultrasound, utilizes high-frequency sound waves to create real-time images of internal organs, primarily by employing a transducer that emits and receives sound echoes. It has various applications in pregnancy, diagnostics, and therapeutic procedures but has limitations in imaging certain body parts. The physics of sound waves, including frequency, amplitude, and acoustic impedance, significantly influence the quality and characteristics of the ultrasound images produced.

1. Introduction to Ultrasonography
Introduction to Ultrasonography
Dr Gameli Kofi Seadzi

2. Ultrasound, also called sonography, uses sound
waves to develop images of internal organs of the
body.
A component of the equipment called transducer
emits high-frequency sound, (inaudible to human
ears) and then records the echoes as the sound
waves reflected back.
The reflected wave is used to determine the size,
shape, and consistency of soft tissues and organs.
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3. • This information is relayed in real time to
produce images on a computer screen.
• Ultrasound technicians, or sonographers,
have special training in how to perform the
test.
• Then a radiologist or doctor will interpret
the ultrasound images.
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4. Uses of the ultrasound
Uses of the ultrasound
• Pregnancy.
– Dating: age of pregnancy; due date.
– Type of conception:
• twins or other multiples
• ectopic pregnancies.
– Birth defects and congenital malformations
– Placental characteristics,
– Presentation: breech cephalic or transverse.
– Sex determination
– Size of baby is just before delivery.
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• Other uses of sonography in medicine
– Diagnostics. Doctors employ ultrasound imaging in
diagnosing a wide variety of conditions affecting the
organs and soft tissues of the body
– Use during medical procedures. Ultrasound
imaging can help doctors during procedures such as
needle biopsies
– Therapeutic applications. Ultrasounds sometimes
are used to detect and treat soft-tissue injuries.

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• Ultrasounds have some diagnostic limitations,
because sound waves do not transmit well
through
–parts of the body that may hold air or gas, such as the
lungs or bowel.
–Fatty tissue in obese patients.

7. Other types of ultrasound
Other types of ultrasound
• Most ultrasounds are done using a transducer
on the surface of the skin.
• Sometimes, a better diagnostic image is
obtained by inserting a special transducer into
one of the body's natural openings:
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8. – In a transvaginal ultrasound, a transducer wand is
placed in a woman’s vagina to get better images of
her uterus and ovaries.
– A transrectal ultrasound is sometimes used in the
diagnosis of prostate conditions.
– A trans esophageal echocardiogram uses the
transducer probe in the esophagus so that the
sonographer can obtain clearer images of the heart
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Physics of sound waves:
Sound speaker produces sound by vibrating in-out repeatedly.

11. • Sound wave: of peaks and troughs that propagate
through the transmitting medium, eg air.
• Frequency – number of waves passing a given point
per unit time (sec). Measured in cycles per sec = Hz
• Wavelength – the distance between two peaks of the
sound wave.
• Period: the time between two peaks; measured in
seconds
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• Frequency X Wavelength = Speed
– The speed of sound is fairly constant in any medium,
and so frequency is inversely proportional to the
wavelength.
– so to increase the frequency reduce the wavelength.
– and to decrease the frequency, increase the
wavelength.
– Sound of lower frequency travel farther from the
source

14. Amplitude – the height of each wave and depicts the
Amplitude – the height of each wave and depicts the
loudness of the sound.
loudness of the sound.
The Amplitude has no mathematical relationship with
The Amplitude has no mathematical relationship with
either the frequency or the wavelength.
either the frequency or the wavelength.
It is the extent to which particles are displaced in the
It is the extent to which particles are displaced in the
transmitting medium eg air.
transmitting medium eg air.
The amplitude determines the loudness of the sound
The amplitude determines the loudness of the sound
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15. • Sound frequency ranges
– Audible range 20 – 20,000Hz (sonic range)
– Sub-sonic or infra –below 20Hz
– Ultra-sonic – above 20,000Hz
• Ultrasound defined as the sound waves above the
audible limit. i.e. 1 mHz to 20 mHz
• In ultrasonography a transducer produces the
ultrasound by crystals changing shape when electric
current is passed through. (Piezo Electric Effect).
• The transducer can also covert sound waves back to
electricity.
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16. Behaviour of sound in tissue
Behaviour of sound in tissue
Ultrasound transducer
• Converts electrical impulse into (ultra) sound
waves
• US waves sent through tissue and reflected back
to transducer (echo)
• Received wave is converted back into electrical
energy
• Transmitted to the screen monitor in real time
and image formed on screen (the skin line).
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17. • At standard temperature and pressure (STP)
sound travels at 343m/sec through air.
• Lungs transmit sound at 600m/sec
• Bone transmit at 4,080m/sec
• Soft tissue averages 1,540m/sec
• 13 micro sec - round trip travel time from
transducer to a 1 cm thick tissue and return.
– 26 micro sec = 2 cm of tissue
– 130 micro seconds = ?
– 1300 micro seconds = ?
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18. • Depth – function of the distance travelled to and fro
transducer
• Brightness – volume or intensity of the returning echo.
louder echo results in brighter image
silent echo produces darker image
• Skin line – processed reflected echo at each linear plain
of reflection.
• Several skin lines used to form a 2D image on the screen.
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19. • Resolution of image: how detailed the image is; and
ability to differentiate between two images.
• Penetration: how deep the image goes
• Increasing frequency improves resolution.
• Decreasing frequency decreases resolution.
• Converse true for penetration
• Increase frequency reduces penetration..
• Increasing the frequency improves resolution but
reduces penetration.
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20. Spatial Resolution
Spatial Resolution
• Ability to differentiate between two different points
in space
• Higher frequency better resolution
• Concept of focal zone of transducer – waves
converge then divert. The narrowest portion of
convergence known as the focal zone.
• Best resolution obtained at the focal zone at any
frequency.
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21. Acoustic Impedance
Acoustic Impedance
• This is the resistance to the travel of sound through a
tissue.
• Sound is reflected or transmitted depending on the
acoustic impedance of the two tissues that are in
proximity.
• The larger the difference two different tissues in close
proximity, the higher the resolution.
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22. Types of reflection
Types of reflection
• Spectral reflection
– Lots of waves reflected
– Smooth
– Homogenous
– bright
• Diffused reflection
– Wave scattered
– Less amount returned
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23. Refraction
Refraction
• Bending of sound beam as the speed of travel
changes.
• Slow into fast:
– Produces a wide angle of deflection
• Fast into slow:
– The angle of deflection is narrow
• Refraction is important in the recognition of artefacts.
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24. Attenuation
Attenuation
• Decrease in the amplitude of sound over a distance.
• For example in audible sounds attenuation results in
not hearing the sound when farther away from the
source.
• Increasing the frequency increases the attenuation of
sound.
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25. Questions
Questions
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