Refrigeration – Storage of solidified or liquified gas – Including cryostat
Reexamination Certificate
2000-03-17
2001-09-25
Capossela, Ronald (Department: 3744)
Refrigeration
Storage of solidified or liquified gas
Including cryostat
C062S003100, C062S610000, C062S919000
Reexamination Certificate
active
06293111
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the preparation of hyperpolarized helium gas at high pressure.
BACKGROUND
Hyperpolarized helium is presently used in magnetometry for the detection and measurement of weak magnetic fields. A new application of hyperpolarized helium is the in vivo exploration of the respiratory airways in humans. The principle consists of the patient inhaling a gaseous mixture containing hyperpolarized helium, followed by performing magnetic resonance imaging (MRI) to visualize the pulmonary ventilation. The imaging can be performed in a conventional strong-field tomograph (>1 tesla) or in a tomograph with a weaker field, possibly dedicated to that application. The inventors have published a report in the Académie des Sciences de Paris, Vol. 230, Series IIb, p. 671-700, 1997, describing various aspects of
3
He gas NMR in the live lung as well as the equipment for the performance of an in vivo NMR. This type of application requires the production of hyperpolarized gas with a pressure that is sufficient to allow inhalation (P≧1 bar).
Also known in the art are various processes and installations for the production of hyperpolarized helium. The general principle is based on optical laser pumping. As an example, French patent FR 8914894 describes an atomic or molecular vapor cell for optical pumping according to the prior art. The gas from this cell is constituted of a mixture of helium-3 and helium-4. However, the apparatus of the prior art only allows polarization of helium gas at low pressure, which then must be compressed at the outlet of the cell. Compression without loss of polarization of the helium gas is delicate and requires complex or expensive equipment.
The prior art also discloses two solutions for compressing the hyperpolarized helium: a mechanical compression technique using a nondepolarizing device developed by the group of Professor E. Otten of the University of Mainz and a cryogenic compression technique described in French patent FR 9601973.
FR '973 concerns an installation for the production of polarized helium-3, comprising a storage reservoir of helium-3 in liquid phase. The production of helium-3 with this type of installation requires an accumulation phase, an optical pumping phase and an evaporation phase enabling delivery of polarized helium-3.
Thus, it would be highly advantageous to resolve these drawbacks and difficulties relative to noteworthy compression by developing a process which avoids the use of sophisticated mechanical compressors and allows the production of hyperpolarized helium at high pressure with simple equipment.
SUMMARY OF THE INVENTION
The invention relates to a process for the preparation of hyperpolarized helium gas at high pressure employing an optical pumping step using a resonant wavelength close to about 1083 nanometers in a helium gas formed by pure helium-3 isotope or by a mixture of helium-3 and helium-4 isotopes, characterized in that the helium gas is subjected to a magnetic field of about 0.01 to about 1 tesla during the optical pumping step, and confined during this optical pumping step to a pressure higher than about 10 millibar (1000 pascal).
Advantageously, the helium gas is confined in a cell of generally cylindrical form presenting a transparent front surface for excitation by a laser beam, the magnetic field being created by electric coils or by a permanent magnet, antennas or electrodes producing an RF field for the creation of a plasma.
The invention also concerns a device for the preparation of hyperpolarized helium gas at high pressure comprising a helium gas confinement cell and an excitation laser, characterized in that it also comprises means for generating a magnetic field of about 0.01 to 1 tesla during the optical pumping stage.
REFERENCES:
patent: 5642625 (1997-07-01), Cates, Jr. et al.
patent: 5934103 (1999-08-01), Ryan et al.
patent: WO 95/27438 (1995-10-01), None
patent: WO 97/29836 (1997-08-01), None
Normal and Abnormal Pulmonary Ventilation: Visualization at Hyperpolarized He-3 MR Imaging, Hans-Ulrich Kauczor, MD et al., Radiology, vol. 210, No. 2, pp. 564 568, Nov. 1996.
Darrasse Luc
Guillot Geneviève
Nacher Jean-Pierre
Tastevin Geneviève
Capossela Ronald
Centre National de la Recherche Scientifique
Schnader Harrison Segal & Lewis LLP
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