Signal sources in PET.

Abstract

Positron emission tomography (PET) is the most accurate and versatile tracer method to measure in-vivo physiological variables in human brain. Since only tracer amounts of indicator substances are used, not only blood flow and energy metabolism can be measured, but also neurotransmitter synthesis (e.g., dopa decarboxylase activity with 18F-6-fluoro-L-dopa) and neuroreceptor binding capacity (many tracers, most frequently labeled with 18F or 11C have been described, for comprehensive reviews see Frost, 1990, Stöcklin et al., 1992). Recently, experimental competition studies of receptor ligands with endogeneous ligand, released by pharmacological stimulation, have been performed successfully (Carson et al., 1995). Yet, this brief overview will concentrate on measurements of blood flow and energy metabolism that are of more direct relevance to optical imaging methods. Table 1 shows commonly used isotopes and tracers to measure cerebral blood flow (CBF), glucose metabolism (CMRGlu), and oxygen metabolism (CMRO2). The short half-life times permit application of significant doses (up to 200 MBq 18F, up to 5000 MBq 15O) resulting in low-noise images due to high countrates with effective whole body doses of less than 5 mSv (the value tolerated for investigations in normal volunteers by current german law, and 1/10 of the dose tolerated for yearly professional exposure). Modern tomographs acquire data three-dimensionally (without septa between planes) with high efficiency from the whole brain simultaneously (Townsend et al., 1991).KeywordsPositron Emission TomographyPositron Emission Tomography MeasurementLocal Cerebral Blood FlowCerebral Blood Flow ChangeBrain Positron Emission TomographyThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.