Positron emission tomography—a new technique for studies of the central nervous system

Abstract

KEY WORDS. Positron emission tomography, positron camera, central nervous system, brain imaging, brain studies. S U M M A R YPositron emission tomography (PET) has become an important tool to study the central nervous system. Examples of such studies are cerebral blood flow and metabolism and determination of receptor characteristics of the brain. In the following the basic principles and the physics behind PET are given. Different aspects are discussed such as detector design, image reconstructions and data analyses. Since quantification is essential in PET, data have to be corrected for absorption, scatter and random coincidences. These corrections and their influence on image data are discussed.A review of state-of-the-art PET research of the brain is given.

Neuroimaging for drug addiction and related behaviors

“…PET is based on the physical principles of (1) positron emission and (2) coincidence detection (Eriksson et al, 1990; Burger and Townsend, 2003). The radionuclides which are used in PET imaging emit a positron (β + ), shortly after their generation by a particle accelerator or a cyclotron.…”

“…These radionuclides (e.g., 15 O, 11 C, and 18 F) generally have short half-lives (i.e., they degrade quickly) and can be built into biologically active molecules. The radionuclide-labeled molecules (e.g., glucose or water), also known as radiotracers, thus contain a positron emitting isotope, which decays by emitting a positron from its nucleus (Eriksson et al, 1990). …”

Fluorine-18 labeling of three novel d-peptides by conjugation with N-succinimidyl-4-[18F]fluorobenzoate and preliminary examination by postmortem whole-hemisphere human brain autoradiography

“…This hypothesis was proved to be true by Ernest Lawrence et al in Berkeley, California who had already started working with accelerating particles between two D-shaped magnets, called a cyclotron, to produce high energy protons and deuterons that could bombard elements to explore the nature of the atomic nucleus 5 The term molecular imaging can be defined as the non-invasive visualisation of biological processes in vivo at the molecular or cellular levels using specific imaging tracers 7,8 . Positron emission tomography (PET) is a non-invasive molecular imaging (in vivo) technique that allows for the localisation of a molecule labelled with positron emitting nuclides 9 , based on the detection of positron annihilation radiation and subsequently processing of raw data onto an image 10,11 . PET was developed at the end of 1970s [12][13][14] , but the full potential of the technique was not acknowledged outside the scientific community until 1990s 15 .…”

“…PET imaging agents are radiolabelled with positron emitting radionuclides, such as 11 C, 18 F, 13 N and 15 O, which are the radioisotopes of the stable natural elements of 12 C, 19 F, 14 N and 16 O, respectively, and they decay (with different half-lives, Table 1) by the emission of a positively charged particle, called positron. For example, 11 C-radioisotope decays by positron emission and forms the stable nuclide boron, 11 B. When the labelled compound (radiotracer or radioligand) is administered intravenously in vivo, the emitting positron from the radio-nuclide travels a short distance in the surrounding matter or wet tissue where it collides with its antiparticle, an electron, and consequently annihilates.…”

“…Photons, which are registered only in pairs (within few nanoseconds) by the PET scanner, are considered to be originated from the same source and thereby, the position of the positron. The distribution of the radioactivity is then visualised and quantified as a function of time 41 after reconstruction 11 and appropriate correction for scatter and random coincidences. The distance travelled by the positron in the surrounding tissue before annihilation is known as positron range.…”