Refrigeration – Cryogenic treatment of gas or gas mixture
Reexamination Certificate
1998-09-30
2001-05-29
Doerrler, William (Department: 3744)
Refrigeration
Cryogenic treatment of gas or gas mixture
C062S062000, C600S420000, C600S431000
Reexamination Certificate
active
06237363
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to equipment and methods used to remove or dispense hyperpolarized gases from containers. The invention is particularly suitable for dispensing sterile or pharmaceutical hyperpolarized gases for Magnetic Resonance Imaging (“MRI”) applications.
BACKGROUND OF THE INVENTION
Conventionally, MRI has been used to produce images by exciting the nuclei of hydrogen molecules (present in water protons) in the human body. However, it has recently been discovered that polarized noble gases can produce improved images of certain areas and regions of the body which have heretofore produced less than satisfactory images in this modality. Polarized Helium-3 (“
3
He”) and Xenon-129 (“
129
Xe”) have been found to be particularly suited for this purpose. Unfortunately, as will be discussed further below, the polarized state of the gases is sensitive to handling and environmental conditions and can potentially rapidly decay from the polarized state.
Hyperpolarizers are used to produce and accumulate polarized noble gases. Hyperpolarizers artificially enhance the polarization of certain noble gas nuclei (such as
129
Xe or
3
He) over the natural or equilibrium levels, i.e., the Boltzmann polarization. Such an increase is desirable because it enhances and increases the MRI signal intensity, allowing physicians to obtain better images of the substance in the body. See U.S. Pat. No. 5,545,396 to Albert et al., the disclosure of which is hereby incorporated by reference as if recited in full herein.
The hyperpolarized gas is typically produced by spin-exchange with an optically pumped alkali metal. The alkali metal is removed from the hyperpolarized gas prior to introduction into a patient to form a non-toxic and/or sterile composition. Unfortunately, the hyperpolarized state of the gas can deteriorate or decay relatively quickly and therefore must be handled, collected, transported, and stored carefully.
The “T
1
” decay constant associated with the hyperpolarized gas' longitudinal relaxation time is often used to describe the length of time it takes a gas sample to depolarize in a given situation. The handling of the hyperpolarized gas is critical because of the sensitivity of the hyperpolarized state to environmental and handling factors and the potential for undesirable decay of the gas from its hyperpolarized state prior to the planned end use, i.e., delivery to a patient for imaging. Processing, transporting, and storing the hyperpolarized gases—as well as delivery of the gas to the patient or end user—can expose the hyperpolarized gases to various relaxation mechanisms such as magnetic gradients, contact-induced relaxation, paramagnetic impurities, and the like.
In the past, rigid containers have been used to transport the hyperpolarized gas from a polarization site to an imaging site such as a hospital. Unfortunately, these conventional transport containers can leave relatively large residual amounts of the gas in the container at the end use point. For example, absent active pumping (which generally introduces unacceptable depolarization to the hyperpolarized gas) an atmosphere of hyperpolarized gas typically remains in the transport vessel, in equilibrium with the ambient air pressure. As such, a larger volume of gas is typically transported to the imaging site to provide the volume desired for clinical use. Unfortunately, the hyperpolarized gas is relatively expensive to produce and this wasted residual gas can disadvantageously escalate the cost of the hyperpolarized product even further. Further, as noted above, conventional pump delivery systems which attempt to extract the gas from the transport container can cause the polarization of the hyperpolarized gas to rapidly decay, thereby limiting the life of the product and providing potentially severe time constraints in which successful clinical imaging can be performed.
Accordingly, there is a need to provide improved extraction systems and containers to minimize the depolarizing effect of the extraction system and to efficiently deliver the hyperpolarized gas to the desired subject.
OBJECTS AND SUMMARY OF THE INVENTION
In view of the foregoing, it is an object of the present invention to provide improved methods to extract hyperpolarized gases from collection and transport vessels in a way which minimizes the de-polarization of the gas attributed thereto.
It is another object of the invention to reduce the residual amounts of hyperpolarized gas in collection vessels or transport vessels at the end use site.
It is yet another object of the invention to provide improved gas dispensing methods and associated containers and apparatus to minimize any degrading effect that the dispensing may have on the polarized life of a hyperpolarized product so that the hyperpolarized product retains sufficient polarization at the end use site to allow effective imaging at delivery.
It is still another object of the present invention to provide dual purpose transport containers which are configured to both collect and transport the hyperpolarized gas.
It is another object of the present invention to provide improved containers which are configured to minimize depolarizing activity associated with the dispensing and delivery of the hyperpolarized gas to a subject.
It is yet another object of the invention to provide methods and apparatus which can minimize the de-polarizing effects on the hyperpolarized state of the gas attributed to active dispensing of the gas from a polarization cell, collection, or transport vessel.
It is an additional object of the present invention to provide a masking method which inhibits the direct contact of hyperpolarized gas with a potentially de-polarizing material or surface.
It is another object of the present invention to provide a polarization verification method which can identify the expiration date of the hyperpolarized gas externally so that hospital personnel can visually determine the status of the gas prior to delivery to a patient.
These and other objects are satisfied by the present invention which is directed to hyperpolarized gas extraction systems, methods, and associated containers which are configured to remove or extract the hyperpolarized gas from a container and reduce the amount of residual gases unrecovered therefrom in a way which minimizes the depolarization of the hyperpolarized gas. In particular, a first aspect of the present invention is directed to a method for extracting a quantity of hyperpolarized noble gas from a container which includes directing a liquid into a container holding a quantity of hyperpolarized gas therein. The liquid contacts the hyperpolarized gas and forces the gas to exit the container separate from the liquid into an exit path operably associated with the container, thereby extracting the hyperpolarized noble gas from the container. In a preferred embodiment, the liquid comprises water which has been sterilized and partially, and more preferably, substantially de-oxygenated and/or de-ionized.
Another aspect of the present invention is directed towards a method similar to that described above, but this method introduces a quantity of fluid (such as gas or liquid) into the container to push the hyperpolarized gas out of the container. The liquid aspect is similar to that described above.
In one embodiment, wherein the fluid is a gas, the gas is preferably non-toxic and suitable for inhalation by a patient. As such, the extraction gas can mix with the hyperpolarized gas to form a hyperpolarized gas mixture as it exits from the container.
In another embodiment, the hyperpolarized noble gas exits the container separate from the extraction gas. In this embodiment, the extraction gas has a density which is substantially different from the hyperpolarized gas. For example, for
129
Xe, the extraction gas is preferably selected so that the hyperpolarized gas has a density which is greater than the extraction gas so that the extraction gas has a density which is less than the hyperpolarized gas. In this embodiment, the exit pa
Bogorad Paul L.
Driehuys Bastiaan
Hasson Kenton C.
Zollinger David L.
Zollinger Geri T. K.
Doerrler William
Medi--Physics, Inc.
Myers Bigel Sibley & Sajovec P.A.
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