| Date | November 2015 | Marks available | 1 | Reference code | 15N.3.HL.TZ0.18 |
| Level | Higher level | Paper | Paper 3 | Time zone | Time zone 0 |
| Command term | Define | Question number | 18 | Adapted from | N/A |
Question
This question is about the use of ultrasound.
Define acoustic impedance.
State the significance of acoustic impedance in the use of ultrasound techniques.
Medical practitioners select the frequency of the ultrasound depending on the diagnosis they are undertaking. Outline the importance of using ultrasound of the appropriate frequency.
Markscheme
product of the density of a substance and the speed of sound in that substance;
if impedance is not matched, large percentage of energy loss at interface;
difference in acoustic impedances necessary for imagery/reflection from organs;
attenuation increases with frequency / deeper objects require lower frequencies;
resolution increases with frequency;
balance required between energy loss/attenuation and image quality/resolution;
Examiners report
Often well answered with clear outlying of the frequency appropriateness in different depths of organs displayed.
Often well answered with clear outlying of the frequency appropriateness in different depths of organs displayed.
Often well answered with clear outlying of the frequency appropriateness in different depths of organs displayed.
