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.
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.
The scans showed signs of lung damage – by highlighting areas where air is not flowing easily into the blood – in the eight who reported breathlessness.