Book contents
- Frontmatter
- Contents
- Acknowledgements
- 1 MR: What's the attraction?
- Part A The basic stuff
- 2 Early daze: your first week in MR
- 3 Seeing is believing: introduction to image contrast
- 4 The devil's in the detail: pixels, matrices and slices
- 5 What you set is what you get: basic image optimization
- 6 Improving your image: how to avoid artifacts
- 7 Spaced out: spatial encoding
- 8 Getting in tune: resonance and relaxation
- 9 Let's talk technical: MR equipment
- 10 But is it safe? Bio-effects
- Part B The specialist stuff
- Appendix: maths revision
- Index
- Plate section
10 - But is it safe? Bio-effects
Published online by Cambridge University Press: 08 October 2009
- Frontmatter
- Contents
- Acknowledgements
- 1 MR: What's the attraction?
- Part A The basic stuff
- 2 Early daze: your first week in MR
- 3 Seeing is believing: introduction to image contrast
- 4 The devil's in the detail: pixels, matrices and slices
- 5 What you set is what you get: basic image optimization
- 6 Improving your image: how to avoid artifacts
- 7 Spaced out: spatial encoding
- 8 Getting in tune: resonance and relaxation
- 9 Let's talk technical: MR equipment
- 10 But is it safe? Bio-effects
- Part B The specialist stuff
- Appendix: maths revision
- Index
- Plate section
Summary
Introduction
For centuries magnets have been attributed with alleged healing and hypnotic powers despite a lack of any scientific evidence or hypotheses on mechanisms. Magnets certainly don't make you better, but are they harmful? In the course of undergoing a clinical MR examination, the patient will be exposed to a static field, time-varying gradient fields and RF fields. Staff normally will only be exposed to the fringe field from B0. In 25 years of MR, there have been ten documented fatalities related to magnet safety, seven of these involving persons with cardiac pacemakers, one involving displacement of an aneurysm clip and one involving a projectile and the other from an unknown cause. You must thoroughly know your institution's safety practices and patient screening procedures, as outlined in chapter 2. Carrying out a metal check on yourself and others will be second nature to you by now, but you can never be too vigilant. The purpose of this chapter is to provide background on the underlying potential biological effects of magnetic fields. In particular we show that:
The main effect of RF exposure is tissue heating. This is restricted to less than 1 °C by monitoring and limiting the SAR (specific absorption rate). Care is required to avoid the heating of leads used for physiological monitoring.
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- Information
- MRI from Picture to Proton , pp. 192 - 200Publisher: Cambridge University PressPrint publication year: 2006