Provision of hyperpolarized [sup 3]H⃗e and its application in MRI

Magnetic Resonance Imaging (MRI) usually relies on magnetization of hydrogen nuclei (protons) in water or molecules in tissue as source of the signal. Biological environments with low proton content, notably the lungs, are difficult to image. Inhaling of hyperpolarized 3He gas opens the possibility to investigate ventilated spaces by MRI. To overcome the loss in signal due to the low density of the gas the nuclear polarization of the 3He spins is greatly enhanced by laser Optical Pumping. For more than three decades Optical Pumping of noble gases has been investigated, using spin exchange scattering (SE) or metastability exchange scattering (ME). Since powerful resonant laser light is available for Optical Pumping, large quantities of 3He gas can be operated. The original interest was the development of dense spin polarized targets for fundamental research in physics. As a spin off, the possibility of MRI of lung tissue filled with hyperpolarized 129Xenon was demonstrated in 1994. Later 3He was used for MRI in a guineapig. While these authors have used the SE method to polarize noble gases, more recently 3He MRI in human lungs was reported by our group where the ME method is in use.