Production of positron-emitting

McCarthy TJ, Welch MJ (1998). The state of positron emitting radionuclide production in 1997. Semin Nucl Med XXVIF235... 

C22-0047. Identify the product of each of the following decay processes (a) Fe emits a positron and a y 55 59... 

The apphcations described here illustrate the wide range of uses for robotic systems. This chapter is not intended to he exhaustive there are many other examples of successful applications, some of which are referenced below. For instance, Brodach et al. [34] have described the use of a single robot to automate the production of several positron-emitting radiopharmaceuticals and TTiompson et al. [3S] have reported on a robotic sampler in operation in a radiochemical laboratory. Both of these apphcations have safety imphcations. CHnical apphcations are also important, and Castellani et al. [36] have described the use of robotic sample preparation for the immunochemical determination of cardiac isoenzymes. Lochmuller et al. [37], on the other hand, have used a robotic system to study reaction kinetics of esterification. 

When a PET isotope is administered to tissue, it emits positrons. These positrons encounter electrons found in tissue, the interaction of an electron and positron results in mutual annihilation and the production of beams of gamma rays directly opposite to each other (Figure 17.10). The... 

Our production parameters for this generator are presented. The Xe-122/l-122 combination, a convenient source of a short-lived (3.6m) positron emitting iodine, is also discussed. Recent developments in rapid iodination procedures will broaden the potential applications of this generator. Finally, preliminary investigations of another generator derived radionuclide that may have promise is described. Tellurium-118 (6d) is the parent of the 3.5 minute positron emitter Sb-118 which may be useful for first pass angiography. 

The production of artificially produced radioactive elements dales back to the early work of Rutherford in 1919 when it was found that alpha particles reacted with nitrogen atoms to yield protons and oxygen atoms. Curie and Joliot found (1933) that when boron, magnesium, or aluminum were bombarded with alpha particles from polonium, the elements would emit neutrons, protons, and positrons. They also found that upon cessation... 

JOLIOT-CURIE. IRENE 11897-195ft. A French nuclear scientist who won the Nohel prize for chemistry with her husband Frederick Joliet-Curie. Their joint work involved production of artiliciul radioactive elements by using t/-rays to bombard boron. They discovered that hydrogen-containing material when exposed to what they considered p rays would emit protons. Tliev were involved in many firsts they gave Ihe first chemical proof of aitillcial transmutation and of capture of alpha particles, and were the firsi to prepare positron emitter. Her career started with a Sc.D. at the Univ ersity of Paris, and included scores of honors and awards. 

Carbon-11 has a very short half-life (just 20.4min) but the chance to substitute a carbon atom in any biological molecule by a positron-emitting nC is a very interesting possibility. This has led to a substantial development of nC-labeled tracers. The short half-life conditions everything and only PET centers equipped with a cyclotron can have a chnical program with nC tracers. The production of the radiopharmaceutical must in these cases be performed just before the imaging study and is usually not started until the patient is already on the PET scanner. 

The first reactor-based slow positron beam was developed by Lynn at Brookhaven [13]. In this system, housed in the reactor building, a copper ball was irradiated in the reactor core (63Cu(n,y)64Cu) and transferred automatically into the source chamber. It was dropped into a cmcible and evaporated on to a tungsten backing. The strong MCu source therefore acted as a self-moderator for the production of slow positrons. At the Munich reactor positrons are produced by pair production by gamma rays emitted in the reaction "3Cd(n,Y)"4Cd [14]. 

The production of short-lived positron emitters has been described in section 12.2. By interaction with electrons, the positrons are annihilated and two y-ray photons of 511 keV each are emitted simultaneously in opposite directions. By measuring these photons by means of a suitable arrangement of detectors, exact localization of the radionuclides in the body is possible. This is the basis of positron emission tomography (PET), which has found broad application in nuclear medicine. The most frequently used positron emitters are listed in Table 19.2. They are preferably produced by small cyclotrons in the hospitals or nearby. 

Positron emitting nuclides have very short half lives, on the order of minutes to tw o hours. This makes operation of a cyclotron and a radiochemistry laboratory essential to the use of PET scanners. is the longest radionuclide with a half-life of 1.87h, making a central production facility within a city feasible for radiopharmaceuticals employing this nuclide. Most clinical PET facilities have on-site cyclotrons and radiopharmaceutical laboratories to allow the use of short-lived isotopes in clinical studies. 

Apart from the electron capture reaction, the 7Be that is produced is partly consumed by proton capture via 7Be(p, a)8B reaction. Under solar conditions, this reaction happens only 0.02% of the time. The proton capture on 7Be proceeds at energies away from the 640 keV resonance via the direct capture process. Since the product 7Li nucleus emits an intense y-ray flux of 478 keV, this prevents the direct measurement of the direct capture to ground state 7-ray yield. The process is studied indirectly by either the delayed positron or the breakup of the product 8B nucleus into two alpha particles. This reaction has a weighted average 5(0) = 0.0238 keVbarn [49]. The 7 Be(p,a)8B reaction cross section measurement has been attempted both by direct capture reactions as well as by the Coulomb dissociation of 8B. For a comparison of the 5 (0) factors determined by the two methods and a critical review of the differences of direct and indirect methods, see [50]. 

More than 3,000 nuclides are known, of which approximately 270 are stable and the remainder are radioactive. The majority of radionuclides are artificially produced in the cyclotron and reactor. In PET technology, only positron-emitting radionuclides are required, and only a few positron emitters of all radionuclides have been suitably utilized in the clinical studies. These radionuclides include 11C, 13N, 18F, 150, etc., and are produced in the cyclotron. The operation of a cyclotron and the production of useful positron emitters are described below. 

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