Assessing pulmonary ventilation and perfusion properties with 19F-MRI

Abstract

Pulmonary imaging with conventional MRI remains challenging, owing to the low proton density of lung tissue and magnetic susceptibility gradients that exist at ubiquitous air-tissue interfaces. The use of exogenous gas agents can overcome these challenges by direct visualisation of inhaled gases within the airways, facilitating assessment of regional ventilation properties. To date, this has largely been achieved in research settings using hyperpolarised-gas MRI, a well-established technique that is capable of providing clinically useful metrics of lung function (e.g. the percentage ventilated lung volume, %VV). However, the requirement for specialised gas polarising equipment and expertise remains a barrier to widespread clinical adoption. Recently, 19F-MRI of inhaled perfluoropropane (PFP) has emerged as a viable approach to human ventilation imaging, offering an alternative to hyperpolarisation with potential for translation to clinical practice. This thesis presents methods for performing human 19F-MR ventilation imaging, focussing on the application of novel scan procedures in healthy volunteers, patients with asthma, and patients with chronic obstructive pulmonary disease (COPD). Initial experiments were conducted within the framework of a dual-centre study (LIFT), enabling the establishment of reproducible imaging methods in healthy volunteers for the evaluation of static %VV measurements across different study sites. The utility of these methods to quantify ventilation defects in patients with asthma and COPD, including bronchodilator response, is reported and discussed. In addition, this thesis explores the feasibility of performing dynamic ventilation and perfusion imaging, employing 19F-MRI of inhaled PFP in combination with a widely used intravenous gadolinium-based contrast agent. Experiments were conducted within the framework of two small feasibility studies (VQ MRI and LungGas). Initial results of these studies are presented, alongside a discussion of the wider implications for future assessment of regional pulmonary ventilation/perfusion properties. This work supports the use of 19FMRI as a novel imaging modality for the assessment of respiratory disease.