Recovery and purification of gases used in medical processes

Details Recovery and purification of gases used in medical processes Recovery and purification of gases used in medical processes

1999-06-18

2002-06-25

Weiss, John G. (Department: 3761)

Surgery

Respiratory method or device

Means for removing substance from respiratory gas

C128S205120, C128S205280, C128S898000

Reexamination Certificate

active

06408849

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention herein relates to the use of gases in medical processes, such as magnetic resonance imaging (MRI). More particularly it relates to the recovery and purification of such gases for reuse.
2. Description of the Prior Art
Various techniques of medical imaging have been developed in the last few years, which provide to physicians the ability to make visual images of patients' internal organs and bodily processes. Such imaging processes have been invaluable for making diagnoses of illnesses and dysfunctions and in giving surgeons the ability to locate and identify internal lesions and tumors before subjecting patients to surgery. Among the techniques widely used is magnetic resonance imaging (MRI).
MRI has been widely used for imaging the brain, heart, kidneys, and spine, since these organs produce relatively strong magnetic resonance (MR) images so that usable images can be obtained. However, other organs, notably the lungs, have not in the past produced such useful MRI images, since magnetic resonance is lower in these organs, particularly in the lungs which are of course hollow and filled with air.
A new technique, called “hyperpolarized noble gas MRI”, has been developed and is reported in Albert and Balamore,
Physics Res. A
[Nucl. Instr. and Meth.], 402:441-453 (1998). The technique involves using the magnetic resonance signal from hyperpolarized noble gases Xe
129
and He
3
to image the lungs or brains of patients who inhaled one of these gases. Images of sufficient quality to study pulmonary disease and to assist in research to elucidate the link between the structure of the lungs and their function have been obtained. The researchers have found that He
3
is easier to hyperpolarize than Xe
129
and yields a stronger MR signal. On the other hand Xe
129
is dissolved much more easily in blood and can pass the blood brain barrier. Consequently it seems likely that He
3
will find greater use in MR imaging of lungs while Xe
129
imaging will be used more for imaging of reach structures of the brain and studies of cortical brain function.
Many details of the enhanced MR imaging with He
3
, as well as details of hyperpolarization, have been recently described in Beardsley, “Seeing the Breath of Life,”
Scientific American
, 280(6):33-34
(June, 1999).
While Xe
129
constitutes approximately one-fourth of all Xe isotopes, xenon itself is a relatively rare element, being found as only about 40 ppb in air, with Xe
129
thus being present as approximately 10 ppb in air. He
3
is even more rare, being present as only slightly more than 1 ppm of all helium. Loss of either of these isotopes during or after an MRI procedure therefore is a very serious matter, not only because of the initial cost of the isotope but also, especially in the case of He
3
, because the vented material can never be recovered. Because there is so little of these materials in the world—some estimates are that the maximum world amount of He
3
is less than 200 kg—enhanced MR imaging using hyperpolarized He
3
or Xe
129
is unlikely to become widely used unless there are methods for recovery and recycling of major portions, and preferably substantially all, of these isotopes from their use in MRI procedures.
Other gases, such as hydrocarbon or fluorocarbon gases which contain C
13
or F
19
isotopes, or those using the isotope P
31
, also find use in various medical processes, which processes may or may not include imaging or hyperpolarization steps. These types of gases also require recovery, usually to avoid environmental air contamination, and when recovered may be advantageously purified and recycled for reuse.
SUMMARY OF THE INVENTION
We have now invented a method for providing a pure gas for use in medical procedures in which the gas is contaminated with other gases during the procedure, and then separating the contaminants and recovering and reusing the decontaminated gas. The method is most advantageously used in medical imaging processes, such as magnetic resonance image (MRI), where hyperpolarized image enhancing noble gases, notably He
3
or Xe
129
, are used for image enhancement in brain and lung imaging, and in which the contaminants are normally the exhalant gases from the imaging patient who inhales and exhales the gas as part of the imaging procedure.
(For brevity herein the method will be described in the context of an MRI process and hyperpolarization of He
3
for use therein. It will be understood that this is exemplary only, and that the method is also applicable to provision of pure gases for other medical processes or procedures, and for use with other recoverable gases. It will also be understood that such gases need not be hyperpolarized as part of the particular medical process or procedure.)
The method is a closed loop system in which the feed image enhancing gas provision is either from a storage tank of recycled, purified gas or from makeup fresh gas. The feed gas passes through a preliminary purification unit in which any contaminants which have gotten into the feed gas from tankage or transport are removed. The gas (e.g., He
3
) is then passed to a hyperpolarization unit in which is subjected to conventional hyperpolarization, as by high energy laser beam. The hyperpolarized gas is discharged from the hyperpolarization unit into a container, such as a gas tight bag, in which it is transported to the location where the imaging procedure is to be conducted. Using as an example an MRI procedure, the patient will inhale gas from the bag and the patient will then hold his or her breath for the short time that it takes for an MRI scan of the patient's lungs to occur. After the scan is completed, the patient will exhale into another larger bag, usually several times to clear as much of the image enhancing gas as reasonably possible from the lungs. After the final exhalation by the patient, the bag of now-contaminated gas will be passed to the recovery and purification system of this invention, along with the original bag containing uninhaled gas, which will have some lesser degree of contamination from having been opened and having had the patient inhale from it. It is anticipated that a major portion of the feed gas will be returned, excepting only those portions of the gas which the patient has failed to exhale, which have been absorbed by the patient's body, or which have leaked into the ambient atmosphere during the time that either bag was opened for the patient to indicate or exhale. When the bags of contaminated gas are received by the recovery and purification system, the contaminated gas is removed from each bag and passed through a series of drying and purification steps to remove the exhalant or other contaminant gases and separate the residual image enhancing gas.
The feed gas from storage or fresh makeup to the hyperpolarization unit is normally under elevated/superatmospheric pressure, although it is discharged from the hyperpolarization unit at essentially atmospheric pressure so that it can be inhaled and exhaled by the patient with minimal loss to the ambient atmosphere. After the contaminated gas is returned to the system, it is moved onward through the system at vacuum/subatmospheric pressure by means of a vacuum pump. Depending on the type of decontamination units used to remove the exhalant gases, the contaminated gas may be compressed to superatmospheric pressure before being passed through the decontamination units, it may be passed through the decontamination units at subatmospheric pressure with pressurizing compression occurring only on the quantity purified image enhancing gas after decontamination, or compression may take place at some point intermediate in the passage through the various decontamination units. Regardless of which of these options is used, the purified gas ultimately will be returned to gas storage under superatmospheric pressure so that it can be recycled and reused for subsequent image imaging procedures.
Exhalant gases (including liquid vapors) whic

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