The consultant radiologist at the centre of a scans re-check at University Hospital Kerry, who worked at the hospital until recently, was a locum and not a permanent member of staff, RTÉ News has confirmed.
The doctor was employed through a locum agency based in Ireland.
RTÉ News has also established that the doctor worked as a consultant radiologist at the Mater Hospital in Dublin in January and February 2006.
The doctor also worked at the same hospital from June 1996 to July 1997.
Yesterday, the Health Service Executive said that no issue arose in relation to the doctor's time in two separate periods at an undisclosed public hospital, which RTÉ has now established is the Mater Hospital, a voluntary hospital funded by the HSE.
The consultant is on the specialist register of the Medical Council.
The doctor previously worked in the UK and in Canada.
The Mater Hospital says that it has instigated an initial internal review, of any variant outcomes, during the short period in question during which the consultant radiologist worked at the Mater.
In a statement, the Mater Misericordiae University Hospital said the radiologist in question worked as a locum in the hospital for a very brief period of time, from February until April 2006.
It said the doctor was also an intern in the hospital for one year from 1996-1997.
The Mater said it is important to note that there are no concerns regarding the quality of work of the radiologist from these brief periods at the hospital.
However, the hospital said that "in light of the situation that has emerged at University Hospital Kerry, the Mater has instigated an initial internal review of any variant outcomes during the short period in question."
It said that patient safety is always its greatest concern as it strives to be the safest hospital in Ireland.
Earlier, University Hospital Kerry said that because of patient confidentiality, it cannot go into the details of the treatment or status of any of the seven serious missed diagnoses cases identified so far.
Some of the cases involve serious missed cancer diagnoses.
The hospital has not confirmed that any of the patients are too ill for treatment.
The Irish Patients Association has said that the health watchdog HIQA should be asked to investigate the University Hospital Kerry scans review controversy.
They said that over the past decade, there had been six major events at hospitals involving radiology rechecks of over 145,000 images.
He asked what had happened regarding the lessons learned and new protocols.
Meanwhile, the hospital says that its review of 46,300 images is being conducted backwards chronologically from July 2017 to March 2016.
The review has almost completed all of the 2017 cases.
To date, over 20,170 images have been examined.
There are around 26,100 still to be reviewed.
The hospital helpline will operate today until 10pm. The number is 1800-742-900.
Lessons must be learned from scan review - ICS
The Head of Advocacy at the Irish Cancer Society has said lessons must be learned from the Kerry scan review.
Speaking on RTÉ's Drivetime, Donal Buggy said it is "disappointing that this is the fifth or sixth time over the last ten years" that a mass review of scans has been required.
He said significant progress has not been made "in dealing with the challenges that have been brought up by previous cases."
Mr Buggy said the fact that the consultant radiologist at the centre of the scans re-check at University Hospital Kerry, was a locum and not a permanent member of staff, "speaks of the challenges of resourcing the health system."
He said relationships built between GPs and consultants help to ensure that issues that arise "get dealt with very quickly."
He said he believes the Health Watchdog HIQA should be charged "with seeing why we have so many cases that require review."
However, Mr Buggy said he believes the Irish healthcare system is "a good one, once you're in it" and it should not be "talked down", rather he said lessons should be learned to ensure that "what is happening stays in the past."