Magnetic Resonance Imaging of Hyperpolarised 129Xe Gas in the Human Lungs

This thesis has mainly focused on methods for hyperpolarised xenon imaging in human lungs at both 1.5 T and 3 T clinical scanners. The results can be summarised briefly as followed: (i) 129Xe human lung imaging is feasible on both 1.5 T and 3T clinical scanners and the ventilation images obtained show comparable SNR and qualitative images (Chapter 3) with slightly higher SNR observed at 3 T. The susceptibility effect, however, does increase at a higher field strength of 3 T, resulting in smaller T2* values in the gas phase 129Xe in a static dephasing regime, and are highly dependent on lung inflation level. (ii) A whole body, unshielded, asymmetric, insert birdcage transmit receive xenon coil was developed for the in-vivo imaging of the human lungs for hyperpolarised 129Xe MRI at 1.5 T. It provides a homogeneous magnetic field and high quality hyperpolarised 129Xe ventilation images. The transparency of the coil to the proton body coil is utilised for localiser imaging prior to xenon lung imaging as well as co-registered 1H/129Xe images in a single breath hold. This coil has also been shown to work with an 8 Channel array coil. (iii) T2* of dissolved 129Xe gas in the human lungs at both 1.5 T and 3 T are very short, were measured at 1.6 ms and 1.0 ms respectively. To achieve better dissolved-phase 129Xe images, one must ensure the minimisation of echo time (TE), and taken into consideration of the chemical shift between 129XeRBC and 129Xeplasma. In conclusion, all findings of this thesis resulted in development and more understanding into the relatively new field of hyperpolarised 129Xe lung imaging. The work built the groundwork towards improvement of 129Xe MRI as a useful and reliable imaging modality.