TE Enriched Sample (E)

Non-ionizing Medical Imaging 2 80 Fig. 2.35 Bundles with different densities of fibres image formed by the objective lens resolution: bending: low less high more Uses A typical use of an endoscope is to examine hollow organs, e.g. the stomach and the colon. The endoscope is inserted directly into these organs through natural openings such as the throat (Fig. 2.36) or rectum. An endoscope is also used in keyhole surgery, where only a few small cuts are made in the human body. Surgical instruments are passed through the endoscope or through additional small holes in the body (Fig. 2.37) Fig. 2.36 Inserting an endoscope into the stomach through the throat oesophagus endoscope Web links Google ‘hkbh minimally invasive surgery’ to learn more about minimally invasive surgery. Fig. 2.37 Using an endoscope in keyhole surgery on chest cavity Resolution As we have seen, each fibre in the coherent bundle transmits light incident on it. Light transmitted in each fibre mixes up and forms a basic unit of the image that can no longer be resolved. Therefore, the resolution depends on how closely the fibres are packed. For a fixed diameter of a bundle, the more and finer the fibres are packed, the higher the resolution (Fig. 2.35). Also, the finer the fibres, the more the bundle can be bent. ( MC: DSE 2013 Q4.3) A typical coherent bundle has a diameter between 0.5 mm and 3 mm, and contains 5000 to 40 000 fibres. See Ex. Q8 on p. 83. Teaching notes Remind Ss that a bundle with finer fibres does NOT give a much brighter image. (See DSE 2013 Q4.3) Teaching notes Remind Ss that, according to DSE 2015 Q4.2, viewing the inner surface of the chest cavity or abdominal cavity is also regarded as viewing the inner surface of an organ with cavity. Sample © United Prime Educational Publishing (HK) Limited, Pearson Education Asia Limited 2023 All rights reserved; no part of this publication may be reproduced, photocopied, recorded or otherwise, without the prior written permission of the Publishers.