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Figure 3

Figure 3. [3H](R)-PK11195 autoradiography overlaps mainly with CD68 labeled activated microglia/macrophages. From: Molecular imaging of microglia/macrophages in the brain.

Combined autoradiography with [3H](R)-PK11195 and immunostaining was performed on a frozen brain section obtained from the frontal cortex of a patient with AD. Immunostaining was performed for astrocytes (GFAP, red) and activated microglia/macrophages (CD68, green). [3H](R)-PK11195 specific binding (black grains) overlapped mainly with CD68 labeled activated microglia/macrophages (merge).

Sriram Venneti, et al. Glia. ;61(1):10-23.
Figure 2

Figure 2. PET imaging of brain activated microglia/macrophages with ligands that bind TSPO. From: Molecular imaging of microglia/macrophages in the brain.

Translocator protein -18 kDa (TSPO) is located at the outer mitochondrial membrane and has a putative five transmembrane helical structure. It forms a hetero-oligomeric complex with the voltage dependent anion channel (VDAC) and the adenine nucleotide transporter (ANT) constituting the putative mitochondrial permeability transition pore. [11C]-labeled TSPO ligands (green) bind to TSPO located in activated microglia/macrophages. The [11C]-radionuclide decays by the emission of a positron, which combines with a free electron, resulting in the annihilation of both particles. Two gamma ray photons (purple) are simultaneously emitted at an angle of 180° from each other. The positron emission tomography (PET) scanner detects both gamma rays from the annihilation to help generate the 3-dimensional PET image.

Sriram Venneti, et al. Glia. ;61(1):10-23.
Figure 1

Figure 1. Principles of Positron Emission Tomography. From: Molecular imaging of microglia/macrophages in the brain.

A simple scheme for PET radiotracer synthesis involves the labeling of a precursor molecule with a chemical synthon (e.g. methyl iodide) containing the PET radionuclide (e.g. carbon-11) to produce the desired radiotracer (top). PET radionuclides such as carbon-11 decay by positron emission to a stable nuclide. A positron is emitted from the decaying nucleus with a characteristic energy spectrum and quickly loses energy by inelastic scattering with electrons in the surrounding medium. Once the positron is in thermal equilibrium with its surroundings (thermalization) it is most likely to interact with a free electron, briefly forming a bound state called positronium before both particles mutually annihilate. The annihilation of the electron and positron results in the conversion of the rest masses of both particles into energy, manifested as the emission of two gamma ray photons each having an energy of 511 kilo-electron volts (keV). The 511 keV annihilation photons travel in opposite directions along a line, forming the basis for PET imaging (middle). A PET scanner is comprised of rings of radiation detectors that are triggered by the coincident detection of two 511 keV gamma rays, forming a line-of-response (LORs) between the detectors in coincidence. LORs are collected and sorted by the scanner in order to reconstruct the radioactivity distribution within the source object (bottom).

Sriram Venneti, et al. Glia. ;61(1):10-23.

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