Protracted bacterial bronchitis (PBB) is a problem in the lungs causing children to have a wet cough for more than 4 weeks. PBB is also known to start before and cause other lung diseases and to affect children's quality of life. It is difficult to know if a child has PBB. Listening to the lungs and measuring a child's breathing are usually normal and so a bronchoscopy (looking in the lungs with a camera) and a type of lung scan called CT are needed to diagnose PBB. These tests involve children being put to sleep under anaesthetic (bronchoscopy) or exposed to radiation (CT) and so are not performed often. PBB is difficult to treat and antibiotics are given for many weeks to make children better. Often this doesn't stop the cough and antibiotics need to be injected into the child to treat the infection. Children have to take large amounts of antibiotics and have regular physiotherapy to help their cough. The only way to know if a child is better is when their parents report their cough has improved which is often unreliable. In this study we will take pictures of children's lungs using a type of scan called MRI, which is safe and does not expose children to radiation. Children breathe in a gas called xenon which fills the lungs. If there is phlegm blocking parts of the lungs, the gas cannot get through and we can see the blockage. This type of picture is the best way to measure early lung disease in children with other lung conditions such as cystic fibrosis and bronchiectasis. Measuring lung disease early will make children with PBBs lives better and mean they have to take less antibiotics. In some children, it will also help to stop lifelong lung diseases such as bronchiectasis.

Inclusion Criteria:

Male and female children aged 5 to 17 years old

• High suspicion of PBB requiring bronchoscopy
• Be able to follow instructions
• English speaking family member

Exclusion Criteria:

Outside of age range

• Significant learning difficulties or inability to follow instructions
• Informed consent / assent has not been provided
• No English-speaking member of the family
• Contraindications for MRI scanning

Participants will be recruited from the Respiratory service at Sheffield Children's Hospital. There are approximately 200 children with PBB diagnosed a year, of which 50 are aged 5 or above. The majority of these children will be eligible for inclusion in the study as most undergo bronchoscopy. It is expected that a high proportion of families will opt for their children to take part in the study due to low risks associated with the 129Xe-MRI being carried out and the benefit of additional clinical information becoming available.