Magnetic resonance imaging in respiratory medicine

At present, pulmonary function tests (PFTs) and computed tomography (CT) are the two principal investigation modalities used in the management of chronic respiratory diseases. However, PFTs provides no spatial functional data, whilst the use of CT is hampered due to the risks associated with ionising radiation. Magnetic resonance imaging (MRI) is a non-invasive and non-ionising imaging modality. Conventional MRI, however, is of little value in imaging the lungs due to poor image quality. New MRI modalities have been developed over the past two decades to enhance the applicability of MRI in respiratory medicine. I undertook a series of studies with the broad aim of defining the practicalities, advantages, and disadvantages of using MRI in the management of patients with respiratory disease. A clinical study was conducted to assess the impact of posture on diaphragm morphology in patients with diaphragm weakness and COPD with hyperinflation on an open upright MRI system. The participants were comprised of 20 healthy individuals, five patients with COPD, and 12 patients with diaphragm weakness. In the healthy participants, the diaphragm morphology changed significantly with the respiratory cycle; posture-related changes were also demonstrated. Compared to healthy participants, however, significant differences in diaphragm morphology related to the breathing cycle were only observed in some of the parameters in the two patient cohorts, and no significant posture-related change was noted. Spirometry was measured in erect and supine positions. No significant correlation was found between the postural change in diaphragm morphology and that in FVC in any of the cohorts. The feasibility of assessing the impact of posture on diaphragm morphology in patients with diaphragm weakness and those with COPD with hyperinflation was demonstrated in this clinical study. Oxygen-enhanced MRI (OE-MRI) is another proton MRI modality studied. A longitudinal cohort clinical study titled ‘Advanced Lung Imaging and Function Testing in Ataxia telangiectasia (A-T)’ is currently ongoing at Nottingham University Hospitals (NUH). This study aims to assess the feasibility of OE-MRI in paediatric patients with A-T in order to evaluate the potential use of this MRI modality in clinical settings. The results of the first year of the study are presented in this dissertation. Ten participants were able to complete the scan process. Signal enhancement in response to the increased concentration of inhaled oxygen and signal inhomogeneity suggestive of ventilation abnormalities were noted on OE-MRI. No statistically significant correlation was found between the OE-MRI-derived parameters and lung clearance index (LCI), which is a lung function test for assessment of ventilation inhomogeneity. Although the initial findings demonstrate the feasibility of this approach, further work is required to optimise the scan sequences and assess the reproducibility of OE-MRI and its role in the long-term management of patients with A-T. Hyperpolarised xenon-129 MRI (129Xe-MRI) was the third modality studied. A clinical study titled ‘Functional Magnetic Resonance Lung Imaging Using Inhaled Hyperpolarised 129Xe’ is currently ongoing at the University of Nottingham. The study aims to develop and optimise 129Xe-MRI capabilities at the Sir Peter Imaging Centre – Queen Medical Centre site (SPMIC-QMC) and assess the safety, feasibility, and reproducibility of 129Xe-MRI. In this dissertation, the imaging data for the healthy participant cohort are presented. Ten healthy participants were scanned; they underwent a total of 106 scans during 28 scan visits. Extensive safety data were obtained, and no serious adverse events occurred. A relatively homogeneous pattern of gas distribution was seen. Dissolved phase spectroscopy and imaging were also obtained. Reproducibility was demonstrated in this healthy participant cohort. With the introduction of functional enhanced MR lung imaging modalities and UTE sequences, the use of MRI for diagnosis and management of respiratory diseases appears a real possibility. However, standardisation of MRI sequences and scan protocol and consensus on image analysis and interpretation are essential before these MR techniques can be used reliably in clinical settings