Before trying these nuclides for PET imaging it is common to wonder what quality images will result from the lower positron abundance and higher energy of I-124 and Zr-89 in comparison to C-11 and F-18. Iodine and Zr both produce 23 percent positron emission, at 680 and 397 KeV, for positron ranges of 1.5 and 1.1 mm, respectively. By comparison F-18 and Cu-64 have energies of 250 and 280 KeV and ranges of about 1 mm. Both iodine and zirconium compare favorably to Ga-68 (see Disselhorst et al., J. Nucl. Med., 51, 4,610-617 (2010), and others). When using very high resolution small animal PET scanners, the intrinsic resolution of the system is slightly reduced when changing from F-18 to I-124. However, in most real-world imaging situations and with the counting statistics generally available the image quality is very similar. While F-18 is comparatively more crisp in high-count images, the difference is minor. Also, it has been uniformly reported that the alternative single photon emissions of these nuclides do not contribute significantly to image noise. The appropriateness of the half-life and labeling chemistry are the most decisive factors in the choice of nuclide. Of course, the availability at a distance is another important factor.
In comparison with Cu-64, Zr-89 has a 30% more abundant positron emission, higher positron energy, and additional higher energy gammas. It's half-life is 78hrs (3.2 days), as compared to Cu-64 at only 13 hours. Zr chelation for binding to biologicals is generally tight and facile, though it is best to use different chelation ligands than are used for copper.
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