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Sorry, couldn't resist. But seriously, although the TOE is considered the 'gold standard', TTE is probably just as good for PFO visualising. Don't know which one the Victoria do, but I would have thought that they would have made sure you were aware of the risks involved during a TOE, so probably the non-invasive test there. There was a study not too long ago that detailed the risk vs. benefit of TOE tests for all divers, just in case, which IIRC concluded that it wasn't worth the risk.
There is another test, Transcranial Doppler, which is the most sensitive of the lot at detecting the presence of a shunt but this will pick up conditions other than PFO and is therefore only useful for ruling one out.
Good luck with the test. Let us know how it goes.