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Basic Physics of Radionuclide Imaging
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4 Basic Physics of Radionuclide Imaging CRAIG LEVIN Molecular Imaging Program, Stanford University School of Medicine, Stanford, California
I. WHERE DO THE NUCLEAR EMISSIONS USED IN IMAGING COME FROM?
I. Where Do the Nuclear Emissions Used in Radionuclide Imaging Come From? II. Relevant Modes of Nuclear Decay for Medical Radionuclide Imaging III. Production of Radionuclides for Imaging IV. Interactions of Nuclear Emissions in Matter V. Exploiting Radiation Interactions in Matter for Emission Imaging VI. Physical Factors That Determine the Fundamental Spatial Resolution Limit in Nuclear Imaging
A. Nuclear Constituents The atomic nucleus consists of neutrons and protons, also known as nucleons. The proton has one unit of fundamental electronic charge, whereas the neutron is electrically neutral. The size and shape of the nucleus depends on the number of neutrons (N) and protons (Z), their particular energy states, and the angular momentum of the nucleus. A typical nuclear diameter is on the order of 10–12–10–13 cm and the density of nuclear matter is roughly 1014 g/cm3. The total number of nucleons in a nucleus (A) is known as the mass number. A nuclide has a particular nuclear composition with mass number A, atomic number Z and neutron number N. The notation we use to identify a particular nuclear composition of an atomic element E with atomic number A = Z + N is ZAE, ZEA, or just AE. Atomic species with identical chemical properties (same Z) but distinct masses (different A) are called isotopes. Nuclides with the same A are called isobars; those with the same N are called isotones. Because chemical reactions involve primarily the outermost orbital electrons of the atom, in general, labeling a compound with a radioactive isotope will not change its chemical behavior. Likewise, the chemical state of an atom
Radioisotope imaging is the in vivo imaging of physiological function using radiation emanating from radionuclides in tracer quantity inside the subject. Physics is involved in almost every step, from the production and decay of the radionuclide to the formation and analysis of the resulting images. In this chapter we discuss some basic physics topics that are relevant to imaging of nuclear emissions. More in-depth discussions can be found in the references given at the end of this chapter, especially in Rollo (1977) and Sorenson and Phelps (1987). Because later chapters deal with the topics of radiation detectors (Part IV) and imaging systems (Parts II, III, and V) used in nuclear emission imaging, we do not cover the topics of radiation detector and imaging system instrumentation physics in full detail in this chapter.
EMISSION TOMOGRAPHY
53
Copyright 2004 Elsevier Science (USA). All rights reserved.
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4 Basic Physics of Radionuclide Imaging CRAIG LEVIN Molecular Imaging Program, Stanford University School of Medicine, Stanford, California
I. WHERE DO THE NUCLEAR EMISSIONS USED IN IMAGING COME FROM?
I. Where Do the Nuclear Emissions Used in Radionuclide Imaging Come From? II. Relevant Modes of Nuclear Decay for Medical Radionuclide Imaging III. Production of Radionuclides for Imaging IV. Interactions of Nuclear Emissions in Matter V. Exploiting Radiation Interactions in Matter for Emission Imaging VI. Physical Factors That Determine the Fundamental Spatial Resolution Limit in Nuclear Imaging
A. Nuclear Constituents The atomic nucleus consists of neutrons and protons, also known as nucleons. The proton has one unit of fundamental electronic charge, whereas the neutron is electrically neutral. The size and shape of the nucleus depends on the number of neutrons (N) and protons (Z), their particular energy states, and the angular momentum of the nucleus. A typical nuclear diameter is on the order of 10–12–10–13 cm and the density of nuclear matter is roughly 1014 g/cm3. The total number of nucleons in a nucleus (A) is known as the mass number. A nuclide has a particular nuclear composition with mass number A, atomic number Z and neutron number N. The notation we use to identify a particular nuclear composition of an atomic element E with atomic number A = Z + N is ZAE, ZEA, or just AE. Atomic species with identical chemical properties (same Z) but distinct masses (different A) are called isotopes. Nuclides with the same A are called isobars; those with the same N are called isotones. Because chemical reactions involve primarily the outermost orbital electrons of the atom, in general, labeling a compound with a radioactive isotope will not change its chemical behavior. Likewise, the chemical state of an atom
Radioisotope imaging is the in vivo imaging of physiological function using radiation emanating from radionuclides in tracer quantity inside the subject. Physics is involved in almost every step, from the production and decay of the radionuclide to the formation and analysis of the resulting images. In this chapter we discuss some basic physics topics that are relevant to imaging of nuclear emissions. More in-depth discussions can be found in the references given at the end of this chapter, especially in Rollo (1977) and Sorenson and Phelps (1987). Because later chapters deal with the topics of radiation detectors (Part IV) and imaging systems (Parts II, III, and V) used in nuclear emission imaging, we do not cover the topics of radiation detector and imaging system instrumentation physics in full detail in this chapter.
EMISSION TOMOGRAPHY
53
Copyright 2004 Elsevier Science (USA). All rights reserved.