Technetium-99m (99mTc) is a generator-produced isotope that is readily available and has a number of advantages over 201Tl for gamma camera imaging.

Imaging in Drug Development

James Nairne, ... Andreas Meijer, in Progress in Medicinal Chemistry, 2015 3.1.1 Technetium-99m Tracers Technetium-99m is produced relatively inexpensively using a generator. Molybdenum-99 suspended on an alumina column decays (t½ = 66 h) to form technetium-99m. The singly charged 99mTcO4− is eluted in preference to the doubly charged 99MoO42− using saline. Commercially available technetium-99m radiotracers are generally prepared by the simple addition of technetium-99m eluted from the generator to a kit vial containing a freeze-dried formulation of the active ingredient. The technetium-99m half-life of 6 h allows time for preparation of the radiotracer, distribution and patient imaging. The energy of the γ-ray emission (140 keV) is ideal for imaging using gamma cameras. Technetium has a rich coordination chemistry with several potential oxidation states [19]. Most nuclear imaging agents contain technetium-99m in the + 5, + 3 or + 1 oxidation states, although it is also present in the + 7 oxidation state in the thyroid imaging agent 99mTcO4−, as formed in the generator. Technetium has good affinity for nitrogen, oxygen, phosphorus and sulphur in the most common oxidation states. The preparation of technetium-99m imaging agents is relatively straightforward (Scheme 1); a kit comprising a reducing agent, usually stannous chloride, a weak chelating agent and the cheland is treated with the generator eluate and the mixture incubated for a short time, often at room temperature, giving a preparation that is ready for injection without purification.

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