- University of Virginia
- Physics Department
A Physical Science Activity
2003 Virginia SOLs
- become familiar with the technological applications of sound; specifically
fetal ultrasound and its purpose in diagnostic procedures.
Ultrasound is a technique that uses sound waves to "look" inside a
human body. Sound waves are bounced into your body and the
reflections of the waves are captured by a machine which transform
them into an image that can be read. Ultrasound is commonly used on
pregnant women to help determine the general health of the fetus. The
sound waves hit the baby and are reflected back to a sensor that
translates the reflections into a picture. Real-time scanners are
used to produce a continuous picture of the moving fetus which is
then depicted on a monitor screen. Very high frequency sound waves of
between 3.5 to 7.0 megahertz (i.e. 3.5 to 7 million cycles per
second) are generally used for this purpose. The sound waves are
produced and received by a small "transducer" that resembles a soap
bar connected by a cable to the machine. It is responsible for
converting the returning sound waves into signals that the machine
can interpret. The transducer also converts signals from the machine
into pulses of sound.
Gel is commonly used when a person gets an ultrasound. The gel is
used to "couple" skin with the ultrasound transducer. The sound
frequencies that are used could not pass through an air-body
interface. The gel acts as a bridge between the machine and the
person getting the ultrasound.
To print out the Student Copy only,
- Complete the following activity sheet.
To print out the Activity Sheet only,
- How does an ultrasound use sound to make a picture?
- Why do you think doctors use ultrasounds instead of
x-rays to take pictures of fetuses?
- Brainstorm different reasons for having a sonogram.
What information could you get from the image?
- The following three images are sonograms at different
stages of pregnancy. Put them in order from youngest
fetus to oldest fetus.
- What parts of the body can you see in each of the
sonograms? At what point do you think that you could
determine the gender of the baby?
- The following image is a three-dimensional sonogram.
Is it easier or harder to see the fetus in this sonogram?
How old do you think that the fetus is, compared to the
above pictures? Label the body parts that you can see.
- The following images are also three-dimensional
sonograms. What interesting thing was discovered about
this baby by using a sonogram?
- What can you determine about the pregnancy from the
Answers to Worksheet
- Ultrasound works similarly to sonar mapping. A sound wave is sent into the
womb, where it bounces off the fetus and comes back. The amount of time that
the sound takes to return and the manner in which the sound reflects off of
the fetus are used to make the image.
- Doctors use ultrasounds because they are much safer than
x-rays. X-rays can be harmful to humans, which is why people
usually wear heavy aprons when getting x-rays of bones. Fetuses
are very sensitive, so x-rays are even more dangerous to them. But
sound waves are not very dangerous at all, and there are no known
side effects of ultrasounds.
- Some uses of ultrasounds are:
- Determine the gender of the baby
- Check for the number of fetuses in the womb
- Check the growth of the child to verify the due date
- Diagnose certain birth defects
- Help select the delivery method
- Guide amniocentesis or chorionic villus sampling
- The order from youngest to oldest is: #1 (8 weeks), #3 (14
weeks), #2 (19 weeks).
- In the sonograms you can see the head, body (chest/stomach),
arms, hands, legs, and feet. If you look closely, you can see
facial features in picture #2. You can determine the gender of the
baby during the second trimester (weeks 13 - 27), so picture #2 or
later is a good estimate.
- It is much easier to see the fetus in the three-dimensional
sonogram. This fetus is 10 weeks old, so it is in-between image #1
and image #3.
- This baby has six toes!
- This is a sonogram of twins.
Look on the internet for information on ultrasounds and for more
sonograms, and have the students analyze them.
is a good site with samples from each trimester. The above pictures
which has a lot of information as well as images. Have the students
bring in sonograms of themselves, if their parents kept them.
Brainstorm other medical uses for sonar, which can also be found on
Students with Special Needs
Each student should be able to participate in this activity.
Click here for further
information on laboratories with students with special needs.
Activity sheet to be completed during the laboratory.