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Physics for medical imaging
Published in Ken Holmes, Marcus Elkington, Phil Harris, Clark's Essential Physics in Imaging for Radiographers, 2021
The electrons in any atom ‘orbit’ the nucleus in energy bands called electron shells. If this did not happen the electrons would exist remotely from the nucleus and randomly within matter. Many aspects of modern physics, including the way X-rays are produced and interact with matter provide us with a strong indication that electron orbitals provide the most likely structural framework for those electrons which are bound to atoms. Everything about modern physics points to the existence of discrete energy bands each of which can contain a predictable maximum number of electrons.
Magnetic Resonance Imaging
Published in Suzanne Amador Kane, Boris A. Gelman, Introduction to Physics in Modern Medicine, 2020
Suzanne Amador Kane, Boris A. Gelman
The spin-up and spin-down states acquire different energies in a magnetic field. We will use and to denote the energies of the spin-up and spin-down states, respectively. The measurements used in MRI utilize changes between possible energy states of the body's nuclei. The spin-up orientation has a lower energy relative to the spin-down one (Figure 8.8a). To describe this situation, we can label an energy diagram for the nucleus's different orientation, just like the energy diagram for electron orbitals in Chapter 3, showing how the presence of the external magnetic field creates two energy levels (possible values of the nucleus's energy).
Dictionary
Published in Mario P. Iturralde, Dictionary and Handbook of Nuclear Medicine and Clinical Imaging, 1990
Chemical shift. (δ) The change in the Larmor frequency of a given nucleus when bound in different sites in a molecule, due to the magnetic shielding effects of the electron orbitals. Chemical shifts make possible the differentiation of different molecular compounds and different sites within the molecules in high-resolution NMR spectra. The amount of the shift is proportional to magnetic field strength and is usually specified in parts per million (ppm) of the resonance frequency relative to a standard.
The use of magnetic resonance spectroscopy for assessing the effect of diet on cognition
Published in Nutritional Neuroscience, 2018
Claire J. Scavuzzo, Christopher J. Moulton, Ryan J. Larsen
Nuclear magnetic resonance (NMR) spectroscopy can be performed on atomic nuclei that possess an intrinsic magnetic moment. The simplest such atom is hydrogen, the nucleus of which contains a single proton. NMR requires the adsorption and re-emission of electromagnetic radiation by the nucleus in the presence of a magnetic field. Because the resonance frequency of each atomic nucleus is sensitive to the particular arrangement of the electron orbitals near the nucleus, each molecule exhibits a characteristic distribution of resonant frequencies, or spectrum, which depends on the structure of the molecule.