Measuring pulmonary gas exchange with hyperpolarised 129Xe magnetic resonance imaging and spectroscopy

The purpose of this thesis was to develop hyperpolarised 129Xe magnetic resonance imaging and spectroscopy (MRI/S) methodology for the assessment of pulmonary gas
exchange and haemodynamics. This was accomplished through the following five subprojects:

1. Validation and development of models to estimate the transfer factor of the lung for carbon monoxide (TLCO) from 129Xe metrics. Applying regression modelling on a voxel-wise level to create parametric TLCO maps provides a useful tool for regional visualisation and clinical interpretation of 129Xe gas exchange MRI.

2. Assessment of compressed sensing (CS)-accelerated dissolved-phase 129Xe imaging. CS reconstruction enabled acquisition time to be halved, and reduced background noise, whilst preserving key gas exchange metrics.

3. Development of a keyhole reconstruction technique to map the amplitude and phase of dissolved 129Xe red blood cell (RBC) signal oscillations in the lung vasculature from dissolved 129Xe MRI data. This may provide a means to probe the effects of the cardiac pulse wave in the pulmonary microvasculature.

4. Evaluation of RBC oscillation amplitude and phase mapping in post-COVID-19 and chronic thromboembolic pulmonary hypertension (CTEPH) patients and initial attempts to validate against established imaging methods and a computational model. 129Xe RBC oscillation amplitude and phase mapping showed potential sensitivity to lung damage at the microvascular level, and agreement with dynamic contrast enhanced MRI and numerical modelling in a small number of CTEPH patients.

5. Development of chemical shift saturation recovery (CSSR) spectroscopy, imaging and analysis techniques to assess pulmonary gas exchange and measure alveolar septal thickness (h) in healthy volunteers and patients with systemic sclerosis and/or pulmonary arterial hypertension. h was significantly greater for the patients than the healthy volunteers. Dynamic CSSR gas uptake imaging allowed for regional quantification of alveolar septal thickness, which could help identify fibrosis in heterogeneous lung disease.