Topic 15: A peep inside

1. Siemens Education Topic 15: A peep inside

2. A peep inside • Course requirements for GCSE Physics • Students should: • Develop knowledge and understanding of the relationship between the properties of electromagnetic waves and their uses • Use scientific theories, models and evidence to develop hypotheses, arguments and explanations • Develop and use models to explain systems, processes and abstract ideas

3. A peep inside • Learning objective • We are learning to: • Explain how MRI scanners produce images • Apply their understanding of waves and particles to this application • Describe typical uses of MRI images

4. A peep inside • How can a doctor make the best possible diagnosis?

5. A peep inside • The importance of images • There are various situations in which medical diagnosis will be assisted by detailed imaging, such as broken bones, tumours, etc and the pros and cons of various imaging technologies, such as ultrasound, CT scans, X-rays and MRI scans, need to be considered • X-rays are often used for the imaging of hard material such as bones • Ultrasound is quick and easy but gives lower resolution images • CT scans are high quality but only work in one plane, whereas MRI scans can work in any plane, producing high quality images of the inside of the body from the desired perspective • CT and X-ray imaging uses ionising radiation

6. A peep inside MRI Scan CT Scan Ultrasound Scan X-ray image

7. A peep inside A hydrogen atom A carbon atom • Atomic structure

8. A peep inside • What does an MRI scanner consist of? • There are four key components: • A powerful permanent magnet • Gradient coils, which produce a variable magnetic field • Radio frequency (RF) coils, which produce radio waves • Scanner, which detects energy emitted from the body

9. A peep inside • How does MRI work? (1) • Although there are many different elements in the body, hydrogen is very common. It is present in water and in fats. Hydrogen nuclei are the key to the production of MRI scans. • Normally, these nuclei spin in random directions around their individual magnetic fields.

10. A peep inside • How does MRI work? (2) • The MRI scanner has a powerful magnet, which produces a magnetic field, many times stronger than that of the Earth. In this magnetic field the nuclei line up either north or south. About half go each way, but there are a few unmatched ones.

11. A peep inside • How does MRI work? (3) • When radio waves are produced by the RF coils, the unmatched nuclei spin the other way. The gradient magnets alter the magnetic field so that images can be produced from any direction.

12. A peep inside • How does MRI work? (4) • When the radio frequency coils are switched off and the pulse of RF waves stops, the extra nuclei return to their normal position, emitting energy.

13. A peep inside • How does MRI work? (5) • The energy released by these nuclei is detected by the scanner, which sends a signal to the computer, which converts it to an image.

14. A peep inside • What advantages does MRI offer? • It can work in any plane: think of the different directions one could slice an apple in. Each slice is a two dimensional view; this is what the images are like. Being able to select the plane offers medical staff real advantages • The images have a very high resolution: the detail is good and it can discriminate between matter that is similar • There are no known biological hazards with MRI: it doesn’t use ionising radiation

15. A peep inside • What are the drawbacks? • Noise: continuous hammering around • Patient has to be still for anything up to 90 minutes: movement causes blurring and requires a repeat scan • Expensive: complex equipment which needs skilled operation and takes time to scan • Claustrophobic: some patients find it unpleasant • Dangerous: magnetic materials can be caused to fly across the room

16. A peep inside • Typical diagnostic application: slipped disc

17. A peep inside Nerves in this area are compromised from the pressure of the prolapsed disc • Typical diagnostic application: slipped disc

18. A peep inside • Typical diagnostic application: sprained wrist (One of the bones in the wrist) (if compressed gives pain, swelling and restriction of movement) (Tendons of the wrist) (Nerve and artery of the ulna bone run through here to the hand)

19. A peep inside • Sample assessment task • This diagram shows a simplified cutaway view of an MRI scanner • Explain how it produces images for clinical diagnosis (6)