Radioisotope positron-emitting

Positron-emitting radioisotope and gamma ray detector system. 

Oligonucleotides can be labeled with organic positron-emitting radioisotopes, such and Br. They are also labeled with metal positron-emitting radio-... 

PET can be used to measure quantitatively the chemical composition of tissues of the body by using appropriately selected compounds labeled with positron-emitting radioisotopes that rapidly distribute between the blood and the tissue of interest. The measurement is based on the determination of the tissue-to-blood partition coeflBcient of the tracer at equilibrium. Knowledge of the tissue-to-blood partition coeflBcient plus the concentration of the compoimd of interest in the vascular compartment permits the calculation of the actual tissue concentration. This concept has been tested by measuring brain carbon dioxide content using C-labeled carbon dioxide as a tracer (31). These measurements were... 

In vitro selectivity, in vivo biodistribution and tumour uptake of annexin V radio-labelled with a positron emitting radioisotope. Brit J Cancer 2003 89 1327-1333. Hickman JA. Apoptosis induced by anticancer agents. Cancer Metast Rev 1992 11 121-139. 

Table 11-12 Photonuclear reactions yielding positron emitting radioisotopes with half-lives close to 20, 10 and 2 minutes, liable to cause interferences in the case of nondestructive carbon, nitrogen or oxygen determination...

Positron emission tomography (PET) is an imaging technique that relies on the emission of positrons from radionucleotides tagged to an injectable compound of interest. Each positron emitted by the radioisotope collides with an electron to emit two photons at 180° from each other. The photons are detected and the data processed so that the source of the photons can be identified and an image generated showing the anatomical localization of the compound of interest. 

A small dose of a soluble fast-decay positron-emitting artificial radioisotope (produced as needed not too far from the PET instrument 6C11, 8015, 9F18 or 37Rb82) is put into human tissue (e.g., blood) the positron typically travels about 1 mm, meets an electron from within the human body, and the pair decays into two y photons of energy 0.51 MeV each, within microseconds to nanoseconds. Two spin states are possible for the positron— electron ion pair before their annihilation singlet and triplet. The annihilation rate for the triplet state depends sensitively on the electron density of the body tissue. Two y counters are set in coincidence mode, and several hundred thousand coincidence events are used to provide valuable tissue information (in addition to a CT scan). 

Another relatively recent technique, in its own way as strange as Mossbauer spectrometry, is positron annihilation spectrometry. Positrons are positive electrons (antimatter), spectacularly predicted by the theoretical physicist Dirac in the 1920s and discovered in cloud chambers some years later. Some currently available radioisotopes emit positrons, so these particles arc now routine tools. High-energy positrons are injected into a crystal and very quickly become thermalised by... 

Studying these isotopes provides fertile ground for physicists and chemists to gain a better understanding of the properties and behavior of nuclei. This field of research also has important applications. For example, radioisotopes—radioactive isotopes—that emit certain particles are critical in some medical treatments such as radiation therapy, which is used to kill cancer cells, and positron emission tomography (PET), which is extremely useful in imaging parts of the body. 

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