FIGURE 7.1 Parametric image of brain that shows the progression of abnormality of proteins in patients with Alzheimer’s disease. SOURCE: Courtesy of Henry Huang, UCLA.

thing is present (i.e., reading an image and making a diagnosis based on where the activity is located and the relative accumulation of the radiotracer to other tissues), and the goal of the estimation task is to determine how much of it is present (e.g., to measure the rate of glucose metabolism from a fluorine-18 fluorodeoxyglucose (FDG)-positron emission tomography (PET) study). The first step to achieve these goals is to acquire the data by accurately measuring the activity of the radioactive tracer in the patient. Once the data are acquired, image reconstruction algorithms are required to generate tomographic image sets of the spatial distribution of radiotracer within the body.

Recent developments involve modeling the physical characteristics of the camera into the iterative reconstruction process to improve image quality and radionuclide quantification. Finally, in addition to basic image display and analysis tools, advanced compartmental modeling tools are needed for those applications in which it is necessary to relate tracer uptake kinetics to physiologic or biochemical measures such as perfusion or receptor concentration, etc. (see Figure 7.1). Thus nuclear medicine imaging will gain from a continuum of improvements. These range from advances in solid-state materials for radiation detectors to increase sensitivity,1 faster


Sensitivity of the instrument is defined as the percentage of radioactive decays that are detected. The sensitivity of a scanner depends on a number of factors, including geometric solid angle coverage and efficiency of the detectors. For single photon emission computed tomography (SPECT) the sensitivity also depends on the collimator, which is needed to define the direction of the gamma ray.

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