and single photon emission computed tomography (SPECT) has further expanded the utility and accuracy of nuclear medicine imaging. By using combined-modality PET/CT and SPECT/CT devices, functional processes can be localized within the body to an anatomically identified or, in some instances, as yet unidentifiable structural alteration. These devices have enhanced the accuracy with which disease can be detected, aided in the determination of the extent and severity of disease, enhanced the accuracy for identifying disease-related risk, and improved the ability to monitor patient response to therapy.
This section describes the use of nuclear medicine imaging for three types of diseases to illustrate its impact on patient diagnosis and management and to identify emerging priorities. The three types of disease are cancer (Section 3.2.1), cardiovascular disease (Section 3.2.2), and neurological disorders (e.g., Alzheimer’s disease) (Section 3.2.3). In addition, the use of nuclear medicine imaging in drug development is discussed in Section 3.2.4.
Cancer develops when cells begin to divide out of control. One hallmark of cancer cells is that they consume larger amounts of glucose than normal cells, because of a shift in energy production. This shift is known as “the Warburg effect” (Sidebar 3.1). Fluorine-18-fluorodeoxyglucose (FDG)-
The Warburg Effect
Cells generate energy in two main ways: oxidative phosphorylation in mitochondria and glycolysis in the cytoplasm. In oxidative phosphorylation, 38 adenosine triphosphate (ATP) moleculesa are generated per glucose molecule. In contrast, two ATP molecules are produced per glucose molecule through glycolysis (a less efficient way of generating energy that requires a greater amount of glucose to produce the same number of ATP molecules). Although cells use both pathways, they primarily switch to glycolysis at times of oxygen deprivation. Nobel Prize-winning German biochemist Otto Warburg observed that cancer cells preferentially generate energy through glycolysis, even in the presence of oxygen. This phenomenon is known as the Warburg effect (Garber 2004).