Radiation counting systems are used for a variety of purposes in nuclear medicine. In vitro (from Latin, meaning “in glass”) counting systems are employed to measure radioactivity in tissue, blood, and urine samples; for radioimmunoassay and competitive protein binding assay of drugs, hormones, and other biologically active compounds; and for radionuclide identification, quality control, and radioactivity assays in radiopharmacy and radiochemistry. In vitro counting systems range…

Nuclear medicine studies are performed with a variety of types of radiation measurement instruments, depending on the kind of radiation source that is being measured and the type of information sought. For example, some instruments are designed for in vitro measurements on blood samples, urine specimens, and so forth. Others are designed for in vivo measurements of radioactivity in patients ( Chapter 12 ). Still others…

Most of the radiation measurement systems used in nuclear medicine use pulse-height analysis ( Chapter 8 , Section C) to sort out the different radiation energies striking the detector. This is called pulse-height or energy spectrometry. It is used to discriminate against background radiation, scattered radiation, and so on, and to identify the emission energies of unknown radionuclides. In this chapter we discuss the basic principles…

All measurements are subject to measurement error. This includes physical measurements, such as radiation counting measurements used in nuclear medicine procedures, as well as in biologic and clinical studies, such as evaluation of the effectiveness of an imaging technique. In this chapter, we discuss the type of errors that occur, how they are analyzed, and how, in some cases, they can be minimized. A Types of…

Most of the radiation detectors used in nuclear medicine are operated in a “pulse mode”; that is, they generate pulses of electrical charge or current that are counted to determine the number of radiation events detected. In addition, by analyzing the amplitude of pulses from the detector, it is possible with energy-sensitive detectors, such as scintillation and semiconductor detectors and proportional counters, to determine the energy…

When radiations from a radioactive material pass through matter, they interact with atoms and molecules and transfer energy to them. The transfer of energy has two effects: ionization and excitation. Ionization occurs when the energy transferred is sufficient to cause an orbital electron to be stripped away from its parent atom or molecule, thus creating an ion pair (a negatively charged electron and a positively charged…

The two most important general types of radiation emitted during radioactive decay are charged particles , such as α particles and β particles, and electromagnetic radiation (photons), such as γ rays and x rays. These radiations transfer their energy to matter as they pass through it. The principle mechanisms for energy transfer are ionization and excitation of atoms and molecules. Most of this energy ultimately is…

Most of the naturally occurring radionuclides are very long-lived (e.g., 40 K, T 1/2 ~ 10 9 years), represent very heavy elements (e.g., uranium and radium) that are unimportant in metabolic or physiologic processes, or both. Some of the first applications of radioactivity for medical tracer studies in the 1920s and 1930s made use of natural radionuclides; however, because of their generally unfavorable characteristics indicated here,…

Radioactive decay is a spontaneous process; that is, there is no way to predict with certainty the exact moment at which an unstable nucleus will undergo its radioactive transformation into another, more stable nucleus. Mathematically, radioactive decay is described in terms of probabilities and average decay rates. In this chapter we discuss these mathematical aspects of radioactive decay. a Activity 1 The Decay Constant If one…

Radioactive decay is a process in which an unstable nucleus transforms into a more stable one by emitting particles, photons, or both, releasing energy in the process. Atomic electrons may become involved in some types of radioactive decay, but it is basically a nuclear process caused by nuclear instability. In this chapter we discuss the general characteristics of various modes of radioactive decay and their general…

Radioactivity is a process involving events in individual atoms and nuclei. Before discussing radioactivity, therefore, it is worthwhile to review some of the basic concepts of atomic and nuclear physics. a Quantities and Units 1 Types of Quantities and Units Physical properties and processes are described in terms of quantities such as time and energy. These quantities are measured in units such as seconds and joules.…

a Fundamental Concepts The science and clinical practice of nuclear medicine involve the administration of trace amounts of compounds labeled with radioactivity (radionuclides) that are used to provide diagnostic information in a wide range of disease states. Although radionuclides also have some therapeutic uses, with similar underlying physics principles, this book focuses on the diagnostic uses of radionuclides in modern medicine. In its most basic form,…