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Medical Physics - Ultrasound
Bats use ultrasounds to navigate in the darkness.

Medical Physics - Ultrasound

This Physics quiz is called 'Medical Physics - Ultrasound' and it has been written by teachers to help you if you are studying the subject at senior high school. Playing educational quizzes is one of the most efficienct ways to learn if you are in the 11th or 12th grade - aged 16 to 18.

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Electronic systems can be used to produce ultrasound waves, which have a frequency higher than the upper limit of hearing for humans (you should know that the range of human hearing is about 20 Hz to 20,000 Hz). Ultrasound can be used as a useful tool in medical imaging; the scientific word for this is ultrasonography but if you don't remember that, don't worry, it won't lose you any exam marks.

1.
Ultrasound waves travel approximately 1,500 m/s in water. A boat sends out an ultrasound wave to the bottom of the ocean. It takes 0.5 seconds for the wave to hit the bottom of the floor and reflect back to the detector. How deep is the ocean floor below the boat?
350 m
375 m
500 m
675 m
This is an example of a non-medical use that you need to know in senior high school. We can use ultrasound to determine depths and distances to underwater obstructions or to detect other vessels
2.
Which of the following are medical uses of ultrasound?
Pre-natal screening
Breaking down kidney stones
Neither of the above, X-rays are used
Both of the above
Pre-natal (also called ante-natal) means 'before the birth', the opposite is post-natal which refers to the time after a birth
3.
The speed of ultrasound in air is 330 m/s. How far away is a car if an ultrasound wave is sent to it along a road and takes 0.1 s to return?
10 m
14.5 m
16.5 m
20 m
distance = speed x time so the answer to this calculation is 330 x 0.05 m. When dealing with echoes, remember that you will often need to half the time otherwise you will be calculating the distance of the journey of the sound there and back
4.
The speed of ultrasound in metal is 5,000 m/s. How far away is a crack in the metal if an ultrasound wave is sent through the metal and is reflected back from the crack to the detector in 0.01 ms?
0.025 m
50 m
50 cm
25 cm
Such short time periods can only be measured electronically
5.
Which of the following can be a use of ultrasound waves?
Sonar
Animal communication
Fetal scanning
All of the above
Ultrasound is not just useful in medical applications
6.
What is the frequency above which a sound wave is known as ultrasound?
5,000 Hz
10,000 Hz
15,000 Hz
20,000 Hz
This frequency is above the limit at which the human ear can hear, however many other animals can hear it easily
7.
Which of the following is/are disadvantages of ultrasound?
Limited resolution
Reflected strongly when passing from tissue to gas
Does not pass well through bone
All of the above
Whilst ultrasound has some disadvantages such as those listed above, the advantages far outweigh them for the applications for which they are used. Using a non-invasive imaging technique for delicate medical issues such as fetal scanning is much more preferred than an intrusive procedure which could cause unnecessary complications
8.
Which formula correctly relates speed, distance and time?
Speed = Distance x time
Distance = Time/speed
Speed = Distance/Time
Speed = Time/ Distance
This equation is used by medical ultrasound scanners to build up an image
9.
Which of the following is/are advantages of ultrasound used in medical scanning?
Non invasive - it is all done from the outside of the body
Inexpensive compared to other scanning methods
It is non-ionising
All of the above
It is safe enough to use to scan a fetus in the womb to check on its progress
10.
Which of the following statements is correct?
Ultrasound waves are partially reflected when they are incident upon a boundary between two different mediums. The time it takes for the reflections to hit a detector can be used to determine the distance the boundary is from the detector
Ultrasound waves are fully reflected when they are incident upon a boundary between two different mediums. The time it takes for the reflections to hit a detector can be used to determine the distance the boundary is from the detector
Ultrasound waves are partially reflected when they are incident upon a boundary between two identical mediums. The time it takes for the reflections to hit a detector can be used to determine the distance the boundary is from the detector
Ultrasound waves are fully reflected when they are incident upon a boundary between two identical mediums. The time it takes for the reflections to hit a detector can be used to determine the distance the boundary is from the detector
If the ultrasound waves were fully reflected, the method would be of no use as you would only be able to observe the first boundary it hits
Author:  Martin Moore

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