A hospital says delays in the reporting of X-ray results has resulted in "no cases of patient harm".
The Care Quality Commission (CQC) had raised concerns about waiting times for radiology results at Kettering General and two other NHS hospitals in England.
It has now called for a limit on how long it takes to report scan results.
Kettering's chief executive Simon Weldon said a backlog, caused in part by the move to a new reporting system in 2016, had "almost been dealt with".
He said: "This led to a large number of images being shown on our system as unreported - when in fact we believed that most of these related to circumstances where a report was not needed but had not been closed on the system.
"Where any delays have been found which could have impacted on patient outcomes we have undertaken a 'harm review' process which has established that so far there have been no cases of patient harm as a result of longer waiting."
The CQC found variations across the country in the time taken to examine and report on scans and X-rays:
- For urgent or fast track cases, this varied from two to five working days
- In A&E, the range was one hour to two working days
- And for GP referrals, while some trusts aimed to report back within 24 hours, others settled for 21 days
An inspection at Kettering General showed, in the year to October 2017, 13% of patients waited longer than four weeks for their report.
The review also said a shortage of radiologists was contributing to delays.
The CQC said it had serious concerns that delays were putting patients at risk at Worcester Royal Hospital, Queen Alexandra Hospital in Portsmouth, and Kettering General.
It has called for national standards for hospitals to ensure timely reporting.