Concern that patients could wait 20 months for some non-urgent scans at Dunedin Hospital was expressed at the Southern District Health Board hospitals' advisory committee.
Chief medical officer (Southland) Dr David Tulloch said long waits could pose a clinical risk.
The fact that a scan might be classed as routine did not mean to say there was not something wrong.
Balclutha GP Dr Branko Sijnja agreed, saying doctors ordered investigations for a reason.
The committee was told that at the end of December the waiting time for routine MRI scans, which was already of concern, had increased by 32 weeks since November, and stood at 20 months.
In her report, diagnostic and support services (Otago) general manager Sonja Dillon said the significant increase in these times was due to a combination of industrial action, increasing demand and the stopping of additional weekend sessions which were being held.
At the end of December, urgent CT scans were taking four weeks, when the target time is two weeks.
Southland fared better, seeing patients in one to two weeks, but it was not meeting its target of same-day service.
At the end of December, Dunedin patients were also having to wait 46 weeks for routine CT scans, up five weeks from the previous month.
In Southland, the comparable wait was six to eight weeks.
Chief operating officer (Otago) Vivian Blake told the committee that before last year's extended industrial action by radiographers, some progress had been made in reducing the wait times for MRI and CT scans.
There had also been an increase in referrals and complex cases.
There had been many referrals for neurology cases where some of the imaging took up to 90 minutes, which had an impact on how many appointments could be offered.
Work had begun on a recovery plan, but resource constraints and the limitations of the existing equipment were "quite an issue".
In her report Ms Dillon said addressing the waiting times would have "further resource implications".
Chief medical officer (Otago) Richard Bunton said one of the precepts for board services was equity of access across the whole region, but there was great disparity between Otago and Southland.
Mrs Blake said the clinical leaders and managers of both Dunedin and Southland hospitals were working together on the question.
Chief operating officer (Southland) Lexie O'Shea said a tender process had begun to see if there were private providers who could help out with ultra sound scans.
In Southland, people are waiting up to 40 weeks for routine ultrasound scans while in Dunedin the time ranges from 18 to 32 weeks.
