Positron-emitting isotopes

Alternatively, smaller on-site cyclotrons can provide immediate access to substantial quantities of short half-life positron-emitting isotopes such as... 

This measures the distribution of a previously administered positron-emitting isotope. PET could be regarded as a form of in vivo autoradiography except that the radioligand is not [ H] but [ 0], [ N], ["C] or [ F], all of which have short half-lives (2, 10, 20 and 110 min respectively) and so the labelled ligand can only be prepared just before use. After intravenous injection the ligand can be located in the brain in a particular place... 

The main feature of the short-lived positron-emitting isotope F is the relative long half-life of 110 min. The ultrashort-lived isotopes C, N, and O have half-lives of 2-20 min, and they must subsequently be produced in the vicinity of the PET scanner(s). Radiopharmaceuticals labeled with F, on the contrary, can be shipped to distant satellite PET centers that are notequippedwith a cyclotron. Several commercial companies are today producing 2-[ F]fluoro-2-deoxy-D-glucose... 

A recent development in nuclear medicine that illustrates how advances in basic research are transformed into practical applications is positron emission tomography or PET. PET creates a three-dimensional image of a body part using positron emitting isotopes. Positrons, positively charged electrons, are a form of antimatter. Antimatter consists of particles that have the same mass as ordinary matter, but differ in charge or some other property. For example, antipro-... 

In PET, positron-emitting isotopes such as C-11, N-13, 0-15, and F-18 are used. Each of these unstable isotopes is characterized by lacking a neutron compared to its stable form for example, C-11 needs one more neutron to become C-12. They undergo positron emission when a proton changes into a neutron ... 

Several direct aromatic fluorinations are carried out with the positron-emitting isotope 18F which is an essential component in the operation of Positron Emitting Tomography (PET). Tyrosine is dissolved in hydrogen fluoride and when fluorinated with 18F-F it produces mainly 3-[ 8F]fluorotyrosine (8) without losing its optical activity. The use of nonacidic solvents reduces the yields considerably.52 3,4-Dihydroxyphenylalanine is similarly fluorinated either in hydro-... 

Fluorine is one of the elements which does not have any natural isotopes, occurring only as 19F. It is possible, however, to generate artificially the positron-emitting isotope 18F either from the lsO isotope or from the Ne atom. 

With positron emission tomography (PET), a positron emitting isotope, e.g. is substituted for a stable atom without altering the chemical behaviour of the molecule. 

PET techniques offer the important advantage in that the drug under study can be firmly labeled with the appropriate positron emitting isotope, usually nC or 1SF. Thus, deposition reflects the pharmaceutical itself, without interference from free isotope. Fluticasone dipropionate, triamcinolone acetonide, and zanamivir have all been labeled and their dose and distribution in the respiratory tract and/or the nasal cavity assessed with PET [48,50,123],... 

Positron emission tomography (PET) imaging is one type of nuclear imaging that utilizes short-lived, positron-emitting isotopes to allow visualization and quantification of biological processes or drug ki-... 

If the source is a positron emitter, a peak at 0.511 MeV is always present. The positron-emitting isotope Na is such an example. It emits only one gamma with energy 1.274 MeV, yet its spectrum shows two peaks. The second peak is produced by 0.511-MeV annihilation photons emitted after a positron annihilates (Fig. 12.8). 

The decay of radioactive isotopes via electron emission, so-called beta decay, is a well-known phenomenon, hi this mode imstable nuclei that have an excessive number of neutrons, for example can emit fast electrons, particles, in order to attain a stable nuclear configuration. Nuclei with insufficient neutrons, such as can obtain stability by emitting fast positrons, particles (the anti-matter equivalents of electrons). Both processes are classified as radioactive f) decay. In each case, the mass munber of the nucleus remains constant but the atomic number changes. There exist several positron emitting isotopes, of which and in particular... 

There exist several positron emitting isotopes of which and... 

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