RT 200 Finals Topic 2: Ultrasound

by **Joshua** Mon Oct 05, 2009 5:02 pm

Topic
2: Ultrasound

Nature
of Sound:

Sound
– Vibrations that travel through the air and are detectable (at
certain frequencies) by the ear.
Synonyms:
Resonance, Echo, Noise
hertz(Hz)
is a unit of frequency.
20-20,000
hertz (Hz) the normal range of hearing of a human – range is in
audible sound.
Any
sound with higher frequency of the audible (Audible- loud enough to
be heard) sound range is called ultrasound.
Subsonic
is a sound in the 0 to 20 Hz range.

The
First Use of Ultrasound:

Ultrasound
was used to detect submarines during WWI (SONAR – SOund NAvigation
and Range), WWII testing begin on human tissue for diagnostic
purpose.

History
of Ultrasound

1870,
the first artificial ultrasound done by curie brothers Jacque and
Pierre who first describe the piezoelectric effect.
Piezo
is a greek word mean press.
The
piezoelectric effect – the change in electric charge distribution
of crystalline materials following a mechanical stress or
electrically polarized when stressed.
Between
1940-1950’s 3 physicians discovered ultrasound waves could form an
image, through sending the waves thru the body and echoes
reflecting.
The
piezoelectric effect is the fundamental physical principle for all
medical ultrasound.

The
Fundamental Physical Principle:

Sound
waves are vibrations passing through a material.
A
sound beam is like an x-ray beam, composed of waves that transfer
energy from one point to another. (radiation passes through vacuum,
sound wave pass through matter)
Ultrasound
imaging utilizes high-frequency sound waves to form an image.
Components
needed to produce an ultrasonic image are transducer, an ultrasound
beam and a cathode ray tube or TV monitor for the display of image.
The
transducer serves two purpose: To transmits sound in pulses or burst
and sense the echoes returning from the previous pulse.
X-rays
are produced when electrons are accelerated to a very high speed and
then decelerated or suddenly stopped. Sound waves are produce in the
transducer by a vibrating crystal.
Vibrations
are passed from one layer of tissue to another. Image structures
depend on the physical characteristics of the tissue such as atomic
number or thickness. (Stiffness, Elasticity, Compressibility)
Impedance
- Total Resistance to the flow of the current.
Acoustic
Impedance (Z) – The reflection of the sound at an interface.

Difference
between ultrasound and radiography: ultrasound pulses continually
loses energy as it passes through the body, where x-ray photon loses
its energy all at once