Covid-19 could be causing lung abnormalities still detectable more than three months after patients are infected, researchers suggest.
A study of 10 patients at Oxford University used 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.
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.