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Chapter 22 dealt with the radiation dose received by patients undergoing nuclear medicine procedures. This chapter deals primarily with the exposure of personnel who work in nuclear medicine clinics and research laboratories and who are exposed to radiation in their normal working environment. Stored radioactive materials, handling of calibration sources, preparation of radioactive materials for patients and phantoms, and proximity to patients or phantoms to whom…
Absorption of energy from ionizing radiation can cause damage to living tissues. This is used to advantage in radionuclide therapy, but it is a limitation for diagnostic applications because it is a potential hazard for the patient. In either case, it is necessary to analyze the energy distribution in body tissues quantitatively to ensure an accurate therapeutic prescription or to assess potential risks. The study of…
The spatial distribution of a radiotracer in the body is time varying and depends on a number of components such as tracer delivery and extraction from the vasculature, binding to cell surface receptors, diffusion or transport into cells, metabolism, washout from the tissue, and excretion from the body. Thus the temporal component often is very important in nuclear medicine studies, and the timing of the imaging…
Image processing refers to a variety of techniques that are used to maximize the information yield from a picture. In nuclear medicine, computer-based image-processing techniques are especially flexible and powerful. In addition to performing basic image manipulations for edge sharpening, contrast enhancement, and so forth, computer-based techniques have a variety of other uses that are essential for modern nuclear medicine. Examples are the processing of raw…
Virtually all modern positron emission tomography (PET) scanners and an increasing number of single photon emission computed tomography (SPECT) systems are integrated with an x-ray computed tomography (CT) scanner. These hybrid imaging systems are capable of acquiring PET or SPECT images, along with spatially registered CT images, in quick succession. This chapter discusses the features of these hybrid systems and describes how the CT scans not…
A basic problem in conventional radionuclide imaging is that the images obtained are two-dimensional (2-D) projections of three-dimensional (3-D) source distributions. Images of structures at one depth in the patient thus are obscured by superimposed images of overlying and underlying structures. One solution is to obtain projection images from different angles around the body (e.g., posterior, anterior, lateral, and oblique views). The person interpreting the images…
Image quality refers to the faithfulness with which an image represents the imaged object. The quality of nuclear medicine images is limited by several factors. Some of these factors, relating to performance limitations of the gamma camera, already have been discussed in Chapter 14 . In this chapter, we discuss the essential elements of image quality in nuclear medicine and how it is measured and characterized.…
The performance of a gamma camera system is defined by the sharpness and detail of the images it produces, the efficiency with which it detects incident radiation, its ability to measure the energy of the incident γ rays (to minimize scatter), and the counting rate it can handle without significant dead time losses. A gamma camera is not capable of producing “perfect” images of the radionuclide…
Radionuclide imaging is the most important application of radioactivity in nuclear medicine. Radionuclide imaging laboratories are found in almost every hospital, performing hundreds and even thousands of imaging procedures per month in larger institutions. In this chapter, we discuss briefly some general aspects of radionuclide imaging, and we describe the basic principles of the most widely used imaging device, the gamma camera, also known as the…
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…