Imaging with non-standard positron emitters

The commonly used positron emitters such as 18F, 11C, or 15O are characterised by a short half-life. Whereas this feature is advantageous in respect to the radiation dose, it is unfavourable if slow biological processes are to be observed. In this case, the non-standard positron emitters, 124I or 86Y, may be used due to their longer half-life of 4 days or 14 hours, respectively. Based on the expertise developed in the INM-5 (nuclear chemistry) over many years, these radionuclides can be produced at very high purity.

In contrast to the short-lived positron emitters, the non-standard positron emitters produce single photons, many of which are emitted in cascade, i.e. practically simultaneously, with the positrons. If the coincidence electronics measures these single photons simultaneously with the annihilation photons following the positron emission, false coincidence events are recorded leading, to a flat background that may disturb the image contrast, as well as the accuracy of quantification.

Previously, our group has performed numerous studies on the accuracy of imaging with 124I or 86Y and has suggested procedures to reduce errors related to the emission of high positron energy, which effects image resolution. First trials with our MR-PET scanners have shown a considerable improvement in image resolution, since the magnetic field leads to a reduced positron range perpendicular to its direction.