Ultrasound imaging

Which one of these non‑invasive medical scans does not expose the patient to ionising radiation?

A CAT

B PET

C Ultrasound

D X‑ray

Your answer

A beam of ultrasound is incident normally at a boundary between two tissues F and G.

The table below shows some data on the two tissues.

	Tissue F	Tissue G
Density of tissue		1.2
Speed of ultrasound in tissue	c	1.5c

What percentage of the intensity of the ultrasound is reflected at the boundary?

A 0.83%

B 8.2%

C 9.1%

D 29%

Your answer

The Doppler effect is used to measure the speed of blood flow in arteries.

Which medical diagnostic method uses this technique?

A barium scan

B CAT scan

C PET scan

D ultrasound scan

Your answer

This question is about the medical use of ultrasound.

In ultrasound scanning, explain what is meant by impedance (acoustic) matching and how it may be achieved.

There are several different types of ultrasound scanning techniques.

Explain how an A-scan could be used to measure the thickness of a patient’s eye lens. You may draw a diagram to help with your answer.

Explain how an ultrasound transducer can emit ultrasound. You do not need to describe the design of the transducer.

Explain how the reflection of ultrasound at a boundary between two tissues depends on the physical properties of the tissues.

Describe the Doppler effect.

Explain how ultrasound is used to measure the speed of blood flow in an artery.

Use Fig. 6.2 to show that the speed of the loudspeaker is 7.5 m s^–1. (i)

The speed of sound in this experiment is 330 m s^–1. (ii)

Calculate the maximum change in frequency f of the sound detected by the microphone.

Hence complete the scale on the y-axis of Fig. 6.2.

Mark with an X on Fig. 6.1 the position of the loudspeaker which corresponds to the

point X on Fig. 6.2.

In their laboratory notes, one student writes about the accuracy of the measurements whereas the other writes about their precision.

Define these terms.

The table shows some data on two tissues in a patient.

Tissue	Density	Acoustic impedance
X		1.5 Z
Y	1.3	Z

Ultrasound in tissue X is incident at the boundary between the tissues X and Y.

What is the percentage of the ultrasound intensity reflected at the boundary?

A 1.7 %

B 4.0 %

C 13 %

D 20 %

Your answer