Simultaneous MRI of Hyper-Polarised 3He and 129Xe in Lungs

R. H. ACOSTA; S. HAN; P. BLÜMLER; S. APPELT; H.W. SPIESS

Snowbird, Utah, EEUU

Congreso; 7th International Conference of Magnetic Resonance Microscopy; 2003

In the last years there is a growing interest in the application of LASER-polarised noble gases in clinical imaging, particularly for the study of the otherwise 'invisible' air spaces in the lung. Different authors use 3He or 129Xe for this purpose. Even though both nuclei are suitable for this studies, they posses unique characteristics that makes them very different in their applications. 3He has a high gyromagnetic ratio, thus providing high sensitivity. Polarization up to 90% can be achieved and it has no physiological effect. On the other hand, 129Xe has a low diffusion coefficient and is lipophilic, it perfuses and dissolves in the blood and even acts as an anesthetic and has a large chemical shift range. From the clinical point of view 3He is ideal for detailed observation of the anatomy of the lung, pore size determination (via self diffusion) and O2 concentration (via paramagnetic relaxation). 129Xe is suited for functionality and perfusion studies, the gas absorbers in blood, a process which can be accurately monitored through it’s chemical shift. The very different gyromagnetic ratio of both gases easily allow double-resonance experiments and hence simultaneous excitation and detection, in this way the information provided by each nuclei can be obtained in a single experiment. In this work we report first attempt to image both isotopes in a gas mixture simultaneously in a phantom and in animal lungs. For this purpose both gases have to be hyper-polarised and suitable partial pressures have to be chosen to compensate the very different signal-to-noise ratios.   The investigation of lungs with MRI methods require extensive procedures when performed on living animals (anesthesia, triggering of heart and breathing rate). On the other hand it is unlikely that one inhalation is exactly identical with the next. For sequence development one wishes to have a simple, static and reproducible model of a lung, which has an almost identical fractal morphology down to the size of the alveolae. We present the procedures for the fixation of entire lungs of small rodents up to pigs. Therefore the lung/heart complex is excorporated and filled with various liquids for fixation using a lower pressure on the outside.  Finally it is dried and can be stored in a non-collapsed state of inhalation. Light-, SEM-Microscopy and MRI techniques using hyperpolarised 3He were employed to verify the intact state of the alveolae on a microscopic level and the morphology of the entire lung.