PET

PET (Positron emission tomography) a nuclear medical imaging technique that produces a three-dimensional image or picture of functional processes in the body. The system detects pairs of gamma rays emitted indirectly by a positron-emitting radionuclide (tracer), which is introduced into the body on a biologically active molecule. Three-dimensional images of tracer concentration within the body are then constructed by computer analysis. In modern scanners, three dimensional imaging is often accomplished with the aid of a CT X-ray scan performed on the patient during the same session, in the same machine.

PET neuroimaging is based on an assumption that areas of high radioactivity are associated with brain activity. What is actually measured indirectly is the flow of blood to different parts of the brain, which is, in general, believed to be correlated, and has been measured using the tracer oxygen-15. However, because of its 2-minute half-life, O-15 must be piped directly from a medical cyclotron for such uses, which is difficult. In practice, since the brain is normally a rapid user of glucose, and since brain pathologies such as Alzheimer’s disease greatly decrease brain metabolism of both glucose and oxygen in tandem, standard FDG-PET of the brain, which measures regional glucose use, may also be successfully used to differentiate Alzheimer’s disease from other dementing processes, and also to make early diagnosis of Alzheimer’s disease.

The advantage of FDG-PET for these uses is its much wider availability. PET imaging with FDG can also be used for localization of seizure focus: A seizure focus will appear as hypometabolic during an interictal scan. Several radiotracers (i.e. radioligands) have been developed for PET that are ligands for specific neuroreceptor subtypes such as [11C] raclopride, [18F] fallypride and [18F] desmethoxyfallypride for dopamine D2/D3 receptors, [11C] McN 5652 and [11C] DASB for serotonin transporters, [18F] Mefway for serotonin 5HT1A receptors, [18F] Nifene for nicotinic acetylcholine receptors or enzyme substrates (e.g. 6-FDOPA for the AADC enzyme). These agents permit the visualization of neuroreceptor pools in the context of a plurality of neuropsychiatric and neurologic illnesses.

See also

fMRI, EEG, dMRI

Papers

• Catana, Ciprian, et al. (2010). Toward implementing an MRI-based PET attenuation-correction method for neurologic studies on the MR-PET brain prototype. Journal of Nuclear Medicine, 51(9), 1431-1438.
• Studholme, C., Hill, D. L. G., & Hawkes, D. J. (1997). Automated 3D registration of MR and PET brain images by multi-resolution optimisation of voxel similarity measures. Med. Phys, 24(1), 25-35.
• Andersson, J. L., & Thurfjell, L. (1997). Implementation and validation of a fully automatic system for intra-and interindividual registration of PET brain scans. Journal of computer assisted tomography, 21(1), 136-144.
• Brooks, R. A., Sank, V. J., Di Chiro, G., Friauf, W. S., & Leighton, S. B. (1980). Design of a high resolution positron emission tomograph: the Neuro-PET. Journal of computer assisted tomography, 4(1), 5-13.
• Roelcke, U., & Leenders, K. L. (2001). PET in neuro-oncology. Journal of cancer research and clinical oncology, 127(1), 2-8.