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Besides mapping the distribution of
water in human bodies, the use of MRI as diagnostic tool is increasingly
employing functional contrast agents to study or contrast entire mechanisms.
Hence the production of specialized contrast agents is of great importance.
Contrast agents in MRI can be classified in two categories. One type of contrast
agents alters the NMR signal of the protons in its surrounding, e.g. lowers the
T1 relaxation time. The other type enhances the NMR signal of specific nuclei.
For hyperpolarized gases the NMR signal is improved several orders of magnitude.
This enables us to image gas filled volume (e.g. lungs, airways,...) where the
proton spin density at Boltzmann-polarisation is far to low to be detected by
means of NMR or MRI. An example is given
by Fig.1. On the left a proton MRI of a chest is shown. On the right the inner
structure of the same chest can be seen by 3He MRI. This one of the
first 3He images in vivo (Ebert et al.; The Lancet, 347 1996)
Our group uses two hyperpolarised nuclei: 129Xe
and 3He. Both nuclei have Spin= 1/2 and can be laserpolarised. This
means that angular momentum from a circular polarised Laserbeam is transferred
to the nuclei. We are able to polarise 129Xe with a home-built
polariser (developed and built by S.Appelt et al.; FZ Jülich). The polarised
3He is provided by the group of Prof. Heil (Institute of physics;
University of Mainz).
During
the last years several topics of hyperpolarised gases imaging has been
investigated. The main results concern "simultaneous NMR-Imaging of
hyperpolarised 3He and 129Xe", "controlling the diffusion
of hyperpolarised gases by admixing buffer gases for biomedical applications",
"direkt molecular solution of hyperpolarised gases through hollow fiber
membranes". Additionally we are working on parahydrogen induced polarisation
(PHIP) and as the newest topic multiple quanten coherences in HP gases are
investigated.
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