There seems to be a bit of flexibility regarding PSA criteria for a PSMA scan depending on an individual's circumstances and which hospital you attend. The higher the PSA and more dense the cancer cells, the greater the chance of these showing up on a PSMA scan. It is possible that cancer cells might show up with a PSA of 0.2 but with a low chance of this a hospital may well want to wait for the PSA to rise a little. With the 68 Gallium PSMA scan it was suggested to me that I have this scan when my PSA reached 0.70 (and this came from the people in Germany who formulated the scan) but improvement over time means a PSA of 0.50 could be a point to have this expensive scan. It does not necessarily mean that because no cancer cells can be seen that none are there. There could be some that are not sufficiently concentrated to be seen. Meanwhile, an MRI might be considered as being appropriate.