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'A' Level Medical Option Questions - Ultrasound

Q9.

(a) State the two physical properties of a material which determine its acoustic impedance.

density of the material
speed of sound in the material

(b) Under what condition is ultrasound strongly reflected at a boundary between two types of material?

When there is a large difference in acoustic impedance

(c) State where a coupling medium or gel is used in an ultrasound scan and explain why it is necessary.

The gel must be placed between the probe and the skin of the patient The gel has similar acoustic impedance to human tissue.
Without the gel being in position there would be trapped air between the probe and the skin. These two media result in a large difference in acoustic impedance. Therefore withair excluded there is maximum transmission of the yltrasound into the patient.

(Total 6 marks)