| Date | May 2011 | Marks available | 4 | Reference code | 11M.3.HL.TZ1.21 |
| Level | Higher level | Paper | Paper 3 | Time zone | Time zone 1 |
| Command term | Define, Explain, and State | Question number | 21 | Adapted from | N/A |
Question
This question is about medical imaging.
A patient is suspected of having a partial blockage in his intestine as it leads away from his stomach. Possible medical imaging techniques include X-ray photography, ultrasound and the use of an endoscope.
When producing the X-ray photograph, the dose is kept to a minimum by a technique called enhancement.
(i) Outline why the dose needs to be kept to a minimum.
(ii) Describe one possible enhancement technique.
(iii) Discuss any extra procedures that are needed to get an appropriate image of the intestine in this situation.
A successful ultrasound scan relies on changes of acoustic impedance around the structure being imaged.
(i) Define acoustic impedance.
(ii) State the SI unit in which it is measured.
(iii) Explain, in terms of acoustic impedance, why gel needs to be applied on the surface of the skin before the ultrasound scan.
Markscheme
(i) X-rays cause ionisations;
which could cause cell damage / increased risk of cancer;
(ii) intensifying screen placed next to the film;
X-rays absorbed by screen and energy re-radiated as light to film;
(iii) barium meal;
to increase contrast between inside and outside the intestine;
(i) density of material×speed of ultrasound in material;
(ii) kgm−2s−1;
(iii) strong reflections take place where there is a large change in acoustic impedance;
gel eliminates air gap between source/receiver of ultrasound and skin surface / acoustic impedance of gel matches that of skin (and
source/receiver);
