Southern District Health Board acting chief operating officer Hamish Brown said clinicians aimed to have only 221 cases on the waiting list, which equates to four weeks’ work for the Dunedin service.
However, the list now stands at 911 patients, 16 weeks of work for the service.
Those 911 people were waiting an average 77 days for a scan, Mr Brown said.
The survey of SDHB waiting lists had also highlighted a discrepancy for Maori patients: the 45 on the waiting list were on average waiting almost three weeks more for a scan than non-Maori.
Mr Brown said the board’s new MRI scanner for Dunedin Hospital, which it ordered last year, was on track to be in use by April, and building work to accommodate it was ongoing.
"This should address overall waiting times but differences between ethnicity groups will be carefully monitored, particularly due to cardiac scanning."
At Southland Hospital, 199 patients were waiting for MRI scans, their median waiting time of 30 days being half of the 60 days Dunedin patients were currently waiting for.
Dunedin also had a longer waiting time than Southland for CT scans, although Mr Brown said that figure was exacerbated by specialty procedures on the list which needed an anaesthetist.
Dunedin’s CT scanner waiting list was 353 patients, who were waiting an average of 44 days each, while Southland Hospital had 152 patients on its list, who were waiting an average of 27 days to be seen.
Last September, a new CT scanner was installed in Dunedin Hospital to address waiting lists, which were well ahead of Ministry of Health targets.
However, Southland, where there is a long-standing shortage of sonographers, had a much longer waiting list than Dunedin for ultrasound scans.
In Southland, 1414 patients were waiting an average 113 days to be seen, while in Dunedin 662 patients were on the waiting list with an average time to be seen of 54 days.
"We are looking to put out expressions of interest to increase outsourcing in Southland," Mr Brown said.
"Recruitment of permanent staff, locums and training is under way on both sites."