D3 Positron emission tomography (PET)

Topic

Positron emission tomography quantifies specific metabolic or molecular processes by administering a radiotracer whose kinetics within the tissue are described by standard compartmental models. Within the tissue, the radiotracer occupies a "free-tracer" compartment that exchanges radiotracer with the plasma: the radiotracer enters this free-tracer compartment from the plasma and can also return from the free-tracer compartment to the plasma. Optionally, the radiotracer may also occupy a second compartment—the specific-binding compartment—when it binds to specific receptors or target proteins, as is the case with radiotracers designed to bind specifically to beta-amyloid or tau protein.

The amount of radiotracer accumulating in each tissue region is clinically summarized by the standardized uptake value, the most widely used semi-quantitative metric in clinical practice: the more radiotracer that accumulates in a region, the higher that region's standardized uptake value.

When the radiotracer also occupies the specific-binding compartment, a metric more specific than the standardized uptake value exists: binding potential, which quantifies the density of binding sites available to the radiotracer in that region. The more binding sites available in a region, the higher the binding potential measured in that region.

There is a variant of positron emission tomography that uses a glucose analogue as the radiotracer; based on the Sokoloff model, this variant allows for the estimation of the regional cerebral metabolic rate of glucose based on the amount of the glucose-analogue radiotracer taken up by each region of brain tissue. The greater the uptake of this glucose-analogue radiotracer in a region, the higher the estimated cerebral metabolic rate of glucose for that region. This regional cerebral metabolic rate of glucose is a sensitive measure of early neuronal dysfunction, making it a useful marker for the neurodegenerative diseases described in other models in this catalog. Ultimately, it is the radiotracer administered during positron emission tomography—whether quantified via standardized uptake value, binding potential, or regional cerebral metabolic rate of glucose—that enables the detection of specific metabolic or molecular processes, including the early neuronal dysfunction characteristic of these diseases.

ID:4299