A review into the work of a locum consultant radiologist has so far identified "major discrepancies" affecting 12 cases.
A full lookback review of 13,030 radiology images was launched last month.
The doctor worked at hospitals run by the Northern Health Trust between July 2019 and February 2020.
The review steering group chair said it was "images in levels one and two that we are most concerned about".
"To date there are 12 level ones and twos [approximately 0.5% of the total number reviewed]," said Dr Seamus O'Reilly, the Northern Trust medical director.
"Most of thes