Covid-19 may be causing lung abnormalities for months months after patients get infected, researchers suggest.
Experts look at 10 patients using a novel scanning technique to identify damage not picked up by conventional scans.
It uses a gas called Xenon during MRI scans to create images of lung damage.
Lung experts said a test that could spot long-term damage would make a huge difference to Covid patients.
The Xenon technique sees patients inhale the gas during a magnetic resonance imaging (MRI) scan.
Oxford University Prof Fergus Gleeson, who is leading the work, tried out his scanning technique on 10 patients aged between 19 and 69.
Eight of them had persistent shortness of breath and tiredness three months after being ill with coronavirus, even though none of them had been admitted to intensive care or required ventilation, and conventional scans had found no problems in their lungs.
The scans mapped the areas where air is not flowing easily into the blood in the eight who reported shortness of breath.
The results have prompted the university to look into 100 more people to see if the same is true of people who had not been admitted to hospital and had not suffered from such serious symptoms.
With the research scientists hope to discover whether lung damage occurs and if so whether it is permanent, or resolves over time.
Prof Fergus Gleeson said: “I was expecting some form of lung damage, but not to the degree that we have seen.”
The risk of severe illness and death increases markedly for the over 60s. But if the trial discovers that the lung damage occurs across a wider age group and even in those not requiring admission to hospital “it would move the goalposts,” Prof Gleeson added.
He believes the lung damage identified by the Xenon scans may be one of the factors behind long Covid, where people feel unwell for several months after infection.