Cutting-edge MRI techniques that use hyperpolarised xenon are transforming respiratory illness trials in Oxford

Magnetic Resonance Imaging is a vital imaging technique that shows us the structure of the lung - but not how well it functions, because air is essentially invisible to MRI.

Patients with chronic respiratory disease have a range of disabling symptoms, including breathlessness and reduced exercise capacity which can lead to social isolation and dependence.  The commonest of these diseases is chronic obstructive pulmonary disease (COPD), which is responsible for about 25-30% of the total impact of chronic lung disease.

Lung function is currently assessed with tests such as spirometry. These tests measure the flow of air during breathing and use this to calculate inhalation and exhalation rates and the volume of air that is moving in and out of the lungs. They assess the severity of disease for the lungs as a whole, but they poorly predict the disability caused by lung disease and this is probably because they measure the lungs as a single unit, ignoring regional abnormalities. This general picture of the lungs is relatively insensitive to mild disease.

Imaging with a CT scan can be used in conjunction with lung function tests, to pinpoint a region of lung with anatomical abnormalities, a tumour for example. CT can also be useful in measuring the extent of emphysema and has relatively good correlation with conventional lung function tests. It is unfortunately limited by being a static imaging test, the dynamic changes seen during breathing cannot be quantified and interpretation of the images is subjective. It also exposes the patient to radiation and this prevents CT from being used repeatedly.

Magnetic resonance imaging has the advantage of being free of ionising radiation and therefore safe in repeated use.  Also it is a dynamic system of imaging, so the movement of the lungs can be seen in real time. Unfortunately, it currently has had limited use in respiratory disease because the functional areas of the lung consist mostly of air spaces that do not generate a magnetic resonance signal. But by inhaling a hyperpolarised inert gas such as xenon can allow the flow of gas into and out of the lung the lung to be seen on MRI.

Hyperpolarised xenon with MR imaging is a new technique that is available in only a few hospitals worldwide - and Oxford is the first in the UK to be in possession of such technology. The patient breathes in the hyperpolarised gas and as it fills the lungs the xenon can be seen filling the air spaces. This technique enables the anatomical changes identified on CT to be visualised on MRI - and will transform the face of clinical trials into respiratory illnesses.