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Nuclear imaging

Dernière mise à jour : lundi 29 août 2011, par Aline NONAT

Positron Emission Tomography (PET) and Single Photon Emission Computed Tomography (SPECT) [1] are highly sensitive imaging techniques (fM-pM) and offer the potential for whole body scanning. However, they have the disadvantage of poor spatial and temporal resolution. Both modalities are based on the use of a radiopharmaceutical and the emission of a γ radiation.
In TEP, a positron-emitting radionucleide (β+) is used (18F, 11C, 64Cu,...). The annihilation of a positron with an electron releases two γ rays which are emitted 180° apart. In SPECT, β emitters are used (99mTc, 111In, 67Ga,...).
In both cases, the emitted γ rays are detected by a γ camera to produce tridimensional images of the radiotracer’s location within the organism.

To date, 18F labelled DFG (DeoxyFluoroGlucose) [2] is the only clinically approved PET radiotracer but its application is limited by the short lifetime of 18F (t1/2 = 109.7 min). However, 64Cu has a significantly longer half-life (t1/2 = 12.7 h) and has the potential for use in PET , (β+, 17.8%, 653 KeV) as well as for radiotherapy, due to the additional high-energy β- particle (38.4%, 579 KeV).

Several families of ligands have been studied in order to optimise the in vivo stability of the 64Cu-radiolabeled complexes and their efficiency as radiopharmaceuticals. Four requirements have been identified : (i) high kinetic and thermodynamic stabilities, (ii) high selectivity for Cu(II) in comparison to other endogenous cations, (iii) a low reduction potential and (iv) a fast kinetic of complexation. [3] [4]

[1C. J. Anderson, M. J. Welch, Chem. Rev. 1999, 99, 2219-2234

[2B M. Gallagher, A. Ansari, H. Atkins, V. Casella, D. R. Christmann, J. S. Fowlers, T. Ido, R. R. McGregor, P. Som, C. N. Wan, A. P. Wolf, D. E. Kuhl, M. J. Reivich, J. Nucl. Med. 1977, 18, 990-996

[3T. J. Wadas, E. H. Wong, G. R. Weisman, C. J. Anderson, Chem. Rev. 2010, 110(5), 2858-2902

[4B. M. Zeglis, J. S. Lewis, Dalton Trans., 2011, 40, 6168-6195