Book contents
- Frontmatter
- Contents
- List of contributors
- Introduction
- Section 1 Image essentials
- Section 2 Biomedical images: signals to pictures
- Ionizing radiation
- 4 Nuclear medicine
- 5 X-rays
- Non-ionizing radiation
- Exogenous contrast agents
- Section 3 Image analysis
- Section 4 Biomedical applications
- Appendices
- Index
- References
4 - Nuclear medicine
Published online by Cambridge University Press: 01 March 2011
- Frontmatter
- Contents
- List of contributors
- Introduction
- Section 1 Image essentials
- Section 2 Biomedical images: signals to pictures
- Ionizing radiation
- 4 Nuclear medicine
- 5 X-rays
- Non-ionizing radiation
- Exogenous contrast agents
- Section 3 Image analysis
- Section 4 Biomedical applications
- Appendices
- Index
- References
Summary
Physics
The modern structure of an atom was first described in 1932 by Niels Bohr with the shell model. In this model, the electrons revolve in stable orbits, or shells, around a positive core, the nucleus. The nucleus, which consists of positively charged protons and electrically neutral neutrons, is the source of gamma rays used in nuclear imaging. In terms of size, the atom is of the order of 10–8 cm while the nucleus is about five orders of magnitude smaller at 10–13 cm. The most successful model used to describe the nucleus is a shell model analogous to the shell model of the atom, except instead of electrons we now have protons and neutrons. The shell model of the nucleus has been used to describe the discrete energy levels present in nuclei depending upon the physical state of the protons and neutrons.
The nucleus has two fundamental forces which determine its stability, the repulsive Coulomb (electromagnetic) force between the same-charge protons, and an attractive strong nuclear force between all neutrons and protons. The strength of these two forces depends upon the number of neutrons (N) and protons (Z) present in the nucleus. We find that in stable light nuclei the number of neutrons and protons is about the same, whereas in heavier nuclei the number of neutrons to provide nuclear stability is larger than the number of protons.
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- Information
- Introduction to the Science of Medical Imaging , pp. 117 - 132Publisher: Cambridge University PressPrint publication year: 2009