PET radiochemistry

With the development of new instrumentation and understanding of reaction behavior under microwave conditions more PET radioligands and PET radiopharmaceutical research are now carried out under microwave enhanced conditions. Two important reviews [8, 9] are available for an up-to-date picture whilst here we discuss some noteworthy, and more recent examples. The benefits of microwaves to PET radiochemistry are also highlighted in other general review articles [111-114]. 

Basic radiochemistry for PET, SPECT — Principles of labeling with radioisotopes and typical successful ligands. ... 

PET radiopharmaceuticals offer enhanced spatial resolution and quantification capabilities compared with SPECT agents. To probe Pgp transport activity, PET-based radiopharmaceuticals have been actively investigated on three fronts (1) use of SPECT scaffolds capable of accommodating PET radionuclides, (2) bioinorganic radiochemistry, and (3) conventional PET organic radiochemistry. 

Nowadays, nuclear medicine has become an indispensible section of medical science, and the production of radionuclides and labelled compounds for application in nuclear medicine is an important branch of nuclear and radiochemistry. The development of radionuclide generators made short-lived radionuclides available at any time for medical application. New imaging devices, such as single photon emission tomography (SPET) and positron emission tomography (PET) made it possible to study local biochemical reactions and their kinetics in the living human body. 

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. 

However, as mentioned earlier, owing to the short half-life of positron emitters ( N—10min, O—2 min, "C—20 min, and F—110 min), ready access to a close by cyclotron and radiochemistry facility is required. This has restricted the wide spread use of the PET in aerosol studies. However, with the rapid growth of PET cyclotrons to meet the demand of the rapid expansion of clinical PET, access to this technology has improved considerably. 

It requires a great deal of logistics in scheduling PET studies at different sites using a mobile PET scanner. The 18F-FDG must be delivered early in the morning, and enough of it should be available to complete the day s schedule. The mobile PET company may have its own cyclotron and radiochemistry laboratory that supplies 18F-FDG to the van, or it may be purchased from another cyclotron facility. 

Figure 8.3. A schematic block diagram showing different components in the 18F-FDG synthesis box. (Reproduced with kind permission of Kluwer Academic Publishers from Crouzel C et al (1993) Radiochemistry automation PET. In Stocklin G, Pike VW (eds) Radiopharmaceuticals for positron emission tomography, Kluwer Academic, Dordrecht, The Netherlands, p 64. Fig. 9)...

The cyclotron facility should be situated at the farthest location from the inside traffic in the PET center, since its operation is not directly related to the patient and the level of radiation exposure is relatively high in this area. It should consist of minimum four rooms cyclotron room, control room, cooling room, and radiochemistry laboratory. The size of these rooms depends on the size of equipment and space available at the facility, and they should be adjacent to each other. 

Advancement in radiochemistry methods has made it possible to develop several probes to study biology. The development of PET radiopharmaceuticals for use in cancer and cancer therapeutics studies is presented in the next section. 

Radionuclides are primarily produced in cyclotrons or reactors, depending on the nuclear reaction required. Very short-lived radionuclides such as C, and are available only in institutions that have a cyclotron facility, and this limits their widespread use. Remote facilities rely on commercially available long- and medium-lived radionuclides In, Ga, etc.) and radionuclides produced by generators (e.g., " Tc). The most commonly used radionuclides in PET and SPECT imaging are listed in Table 1.1. A complete discussion about radionuclide production, labeling conditions, and recent progresses in radiochemistry can be found elsewhere (18-20). 

Schwarz SW, Anderson CJ. Radiochemistry and radiopharmacology. In Christian PE, Bernier D, Langan JK, eds. Nuclear Medicine and PET Technology and Techniques. St. Louis Mosby, 2004 157-183. 

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