Introduction
1.How Ultrasound Works?
2.What is Ultrasound?
3.Different Types of Ultrasound
4.Major Uses of Ultrasound
5.An Ultrasound Examination
How Ultrasound Works :
There
are many situations in which ultrasound is performed. Perhaps you
are pregnant, and your obstetrician wants you to have an ultrasound
to check on the developing baby or determine the due date. Maybe
you are having problems with blood circulation in a limb or your
heart, and your doctor has requested a Doppler ultrasound to look
at the blood flow. Ultrasound has been a popular medical imaging
technique for many years.
What
is Ultrasound?
Ultrasound
or ultrasonography is a medical imaging technique that uses high
frequency sound waves and their echoes. The technique is similar
to the echolocation used by bats, whales and dolphins, as well
as SONAR used by submarines. In ultrasound, the following events
happen:
The ultrasound machine transmits high-frequency (1 to 5 megahertz)
sound pulses into your body using a probe.
The sound waves travel into your body and hit a boundary between
tissues (e.g. between fluid and soft tissue, soft tissue and bone).
Some of the sound waves get reflected back to the probe, while
some travel on further until they reach another boundary and get
reflected.
The reflected waves are picked up by the probe and relayed to
the machine.
The machine calculates the distance from the probe to the tissue
or organ (boundaries) using the speed of sound in tissue (5,005
ft/s or1,540 m/s) and the time of the each echo's return (usually
on the order of millionths of a second).
The machine displays the distances and intensities of the echoes
on the screen, forming a two dimensional image like the one shown
below.
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| Different
Types of Ultrasound |
The ultrasound that we have described so far presents a two dimensional
image, or "slice," of a three dimensional object (fetus,
organ). Two other types of ultrasound are currently in use, 3D ultrasound
imaging and Doppler ultrasound.
3D Ultrasound Imaging
In the past two years, ultrasound machines capable of three-dimensional
imaging have been developed. In these machines, several two-dimensional
images are acquired by moving the probes across the body surface
or rotating inserted probes. The two-dimensional scans are then
combined by specialized computer software to form 3D images.
3D
imaging allows you to get a better look at the organ being examined
and is best used for:
- Early
detection of cancerous and benign tumors
- examining the prostate gland for early detection of tumors
- looking for masses in the colon and rectum
- detecting
breast lesions for possible biopsies
- Visualizing a fetus to assess its development, especially for
observing abnormal development of the face and limbs
- Visualizing blood flow in various organs or a fetus
Doppler
Ultrasound
Doppler ultrasound is based upon the Doppler Effect. When the
object reflecting the ultrasound waves is moving, it changes the
frequency of the echoes, creating a higher frequency if it is
moving toward the probe and a lower frequency if it is moving
away from the probe. How much the frequency is changed depends
upon how fast the object is moving. Doppler ultrasound measures
the change in frequency of the echoes to calculate how fast an
object is moving. Doppler ultrasound has been used mostly to measure
the rate of blood flow through the heart and major arteries.
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Major
Uses of Ultrasound |
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Ultrasound has been used in a variety of clinical settings, including
obstetrics and gynecology, cardiology and cancer detection. The
main advantage of ultrasound is that certain structures can be observed
without using radiation. Ultrasound can also be done much faster
than X-rays or other radiographic techniques. Here is a short list
of some uses for ultrasound:
Obstetrics and Gynecology
- measuring
the size of the fetus to determine the due date
- determining the position of the fetus to see if it is in the normal
head down position or breech
- checking the position of the placenta to see if it is improperly
developing over the opening to the uterus (cervix)
- seeing the number of fetuses in the uterus
- checking the fetus's growth rate by making many measurements over
time
- detecting ectopic pregnancy, the life-threatening situation in
which the baby is implanted in the mother's Fallopian tubes instead
of in the uterus
- determining whether there is an appropriate amount of amniotic
fluid cushioning the baby
- monitoring the baby during specialized procedures - ultrasound
has been helpful in seeing and avoiding the baby during amniocentesis
(sampling of the amniotic fluid with a needle for genetic testing).
Years ago, doctors use to perform this procedure blindly; however,
with accompanying use of ultrasound, the risks of this procedure
have dropped dramatically.
- seeing tumors of the ovary and breast
Cardiology
- seeing the inside of the heart to identify abnormal structures
or functions
- measuring blood flow through the heart and major blood vessels
Urology
- measuring blood flow through the kidney
- seeing kidney stones
- detecting prostate cancer early
In addition to these areas, there is a growing use for ultrasound
as a rapid imaging tool for diagnosis in emergency rooms.
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An
Ultrasound Examination |
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For
an ultrasound exam, you go into a room with a technician and the
ultrasound machine. The following happens:
- You remove your clothes (all of your clothes or only those over
the area of interest).
- The
ultrasonographer drapes a cloth over any exposed areas that are
not needed for the exam.
- The
ultrasonographer applies a mineral oil-based jelly to your skin
-- this jelly eliminates air between the probe and your skin to
help pass the sound waves into your body.
- The
ultrasonographer covers the probe with a plastic cover.
- He/she
passes the probe over your skin to obtain the required images.
Depending upon the type of exam, the probe may be inserted into
you.
- You
may be asked to change positions to get better looks at the area
of interest.
- After
the images have been acquired and measurements taken, the data
is stored on disk. You may get a hard copy of the images.
- You
are given a towelette to clean up.
- You
get dressed.
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