Patent Application
20140123681
The invention relates generally to a method and apparatus for polarizing samples for use in magnetic resonance imaging (MRI).
The present invention relates to nuclear magnetic resonance (NMR) analysis, particularly to nuclear magnetic resonance imaging (MRI) and analytical high-resolution NMR spectroscopy. MRI is a diagnostic technique that has become particularly attractive to physicians as it is non-invasive and does not involve exposing the patient under study to potentially any such as from X-rays. Analytical high resolution NMR spectroscopy is routinely used in the determination of molecular structure.
MRI and NMR spectroscopy lack some degree of sensitivity due to the normally very low polarization of the nuclear spins of the contrast agents typically used. A number of techniques exist to improve the polarization of nuclear spins. These techniques are known as hyperpolarization techniques and lead to an increase in sensitivity. In hyperpolarization techniques, a sample of an imaging agent, for example but not limited to 13C1-Pyruvate or another agent, is introduced or injected into the subject being imaged. Hyperpolarization is not limited to 13C1-Pyruvate or any specific compound (metabolically active or not). As used herein, the term “polarize” refers to the alignment of the nuclear spins of an agent for further use in MRI. Further, as used herein, the term “hyperpolarized” refers to polarized to a level over that found at room temperature and at 1 T, which is further described in U.S. Pat. No. 6,466,814.
In many instances, the imaging agent undergoes this hyperpolarization in an apparatus in close proximity to its end use. This is due to the normally short life time (longitudinal relaxation time T1) of the polarization causing the spins to relax back to the thermal equilibrium polarization. One such technique to polarize nuclear spins uses Dynamic Nuclear Polarization to polarize the spins in the solid state. The apparatus used to produce the hyperpolarized samples is provided with a low temperature space that is in a magnetic field. As typically constructed, the apparatus is equipped with a flow cryostat that includes a vacuum insulated chamber inserted into the bore of a magnet. The cryostat is cooled by way of a stream of a cold cryogen provided by an external cryogen supply through a transfer line and pumping device, and the flow of cryogen into the flow cryostat cools the bore of the magnet and forms the low temperature space.
The pumping devices currently used to provide the stream of cold cryogen are open cycle pumping systems that are undesirable for use in a clinical setting for numerous reasons. First, the open cycle pumping systems are large and generate high levels of noise. Furthermore, the open cycle pumping systems are expensive and cumbersome to operate because of the large quantity of cryogen that is consumed in the pumping process. That is, in order to provide a stream of cold cryogen to the flow cryostat, a sizable portion of the liquid cryogen is evaporated. In an open cycle pumping system, a large measure of this evaporated cryogen is not reclaimable. Thus, a large amount of cryogen is needed to hyperpolarize a sample, which adds significantly to the cost of operating the system.
In addition to adding cost to the operation of the pumping system, the failure to reclaim the evaporated cryogen in an open cycle pumping system also leads to overall system inefficiency. That is, continuous operation of an open cycle pumping system is not possible because of the cryogen loss associated with the hyperpolarization of each imaging agent sample. Therefore, continuous operation for the open cycle systems is only obtained by regular cryogen filling in intermediate reservoirs.
Thus, current hyperpolarization systems are inefficient and expensive to operate. A need therefore exists for a hyperpolarization system that minimizes or eliminates cryogen consumption and is energy efficient. It is also desirable that an improved hyperpolarization system be designed to operate in a manner that minimizes disruption to the surrounding environment and allow for more continuous operation, without the requirement of the operator to handle liquid cryogens, to increase production of hyperpolarized imaging agent samples.
The present invention overcomes the aforementioned drawbacks by providing an apparatus and method for producing hyperpolarized samples for use in magnetic resonance systems. A sorption pump is incorporated into the apparatus to create a closed system for hyperpolarizing. Being a closed system, the apparatus and system loses no cryogen to atmosphere such that there is no need to replenish cryogen in the system.
Therefore, according to one embodiment of the present invention, an apparatus comprises a cooling container containing a cryogenic refrigerant therein, configured to hyperpolarize a plurality of samples therein; a refrigeration system comprising: a refrigerator; and a helium condenser, wherein the helium condenser is separate and positioned exterior to and apart from the cooling container; a sorption pump connected to the cooling container, wherein the sorption pump is separate and spaced apart from the cooling container; a thermal switch configured to connect and disconnect the refrigeration system from the sorption pump; a heater disposed adjoining the sorption pump, configured to heat the sorption pump and promote molecular desorption therein; a single magnetic field producing device in thermal communication with the refrigeration system, wherein the single magnetic field producing device is configured to maintain a selected magnetic field in the apparatus, wherein the single magnet field producing device comprises: a superconducting magnet having a bore therethrough positioned about the cooling container; a magnet vessel to enclose the superconducting magnet, the magnet containing liquid cryogen therein to cool the superconducting magnet; and a magnet condenser configured to recondense helium gas that evaporates due to a heat load to the superconducting magnet, wherein the superconducting magnet is configured to produce a primary magnetic field region about the cooling container for hyperpolarization of the plurality of samples and a secondary magnetic field region offset from the primary magnetic field region that extends axially out from the superconducting magnet, wherein the superconducting magnet is further configured to operate without quench or loss of liquid helium when disconnected from the refrigeration system; and at least one thermal bus connecting the refrigeration system, the helium condenser, the magnet condenser, and the thermal switch, further wherein the apparatus comprises a closed system.
In accordance with another embodiment of the present invention, a polarizing subsystem comprises: a container having a liquid helium bath configured to receive a material to be polarized; a sorption pump to reduce a pressure in the container, thereby to vaporize a portion of the liquid helium bath, the sorption pump comprising: a sorb can configured separate, spaced apart, and exterior to the container; a cooling system comprising: a magnet condenser configured separate, spaced apart, and exterior to the container, configured to recondense liquid helium boiled off therefrom and cool the sorption pump and promote molecular adsorption therein; a thermally conductive link that selectively connects the sorption pump and the cooling system to provide selective cooling to the sorption pump; a heater disposed adjoining the sorption pump, the heater configured to heat the sorption pump and promote molecular desorption therein; a single magnetic field producing device configured to maintain a selected magnetic field for polarizing the material in the apparatus, wherein the single magnetic field producing device is cooled by the cooling system, wherein the polarizer system operates in a closed cyclical thermal cycle alternating between a polarizing phase and a reheating phase based on the thermally conductive link of the sorption pump to the cooling system.
In accordance with yet another embodiment of the present invention, a method for producing a hyperpolarized material comprises: placing a material sample in a vessel containing a liquid helium bath; reducing a temperature of the liquid helium bath with a sorption pump and a refrigeration system, wherein the sorption pump comprises: a sorb can configured separate from and exterior to and spaced apart from the vessel, wherein the refrigeration system comprises: a helium condenser configured separate from and exterior to and spaced apart from the vessel; refilling the liquid helium bath by heating the sorption pump with a heater, the heater being disposed adjoining the sorption pump; positioning a single magnetic field producing device adjacent the vessel, wherein the single magnetic field producing device is configured to product a high homogeneity magnetic field and a fringe magnetic field offset from the high homogeneity field; and polarizing the material sample when the liquid helium bath has been sufficiently cooled by the single magnetic field producing device
In accordance with yet another embodiment of the present invention, a polarizer system comprises: a refrigerator; a magnet condenser; a helium condenser; a thermal bus permanently linking the refrigerator, the magnet condenser, and the helium condenser; a sorption pump selectively linked through a thermal switch to the thermal bus; a heater adjoining the sorption pump; a container containing a cryogenic refrigerant therein, configured to receive a plurality of samples for polarizing therein; a magnetic field producing device in a magnet vessel surrounding the container; wherein the polarizing system is further configured to operate in three separate modes, wherein: a first mode comprises: heating the sorption pump with the heater, thereby releasing helium gas to be cooled and liquefied by the helium condenser, wherein the released helium gas heats the thermal bus, thereby isolating the magnet vessel due to a thermal diode effect at the magnet condenser; a second mode comprises: upon completion of condensation of helium from the sorption pump, turning off the heater and cooling the sorption pump by closing the thermal switch, thereby creating a thermal linkage of the sorption pump, the thermal bus and the refrigerator, and thermally isolating the magnetic field producing device from the thermal bus; and, a third mode comprises: cooling the magnetic field producing device, thereby eliminating a thermal diode effect of the magnet condenser.
Various other features and advantages of the present invention will be made apparent from the following detailed description and the drawings.
The drawings illustrate an embodiment presently contemplated for carrying out the invention.
In the drawings:
Referring to
A refrigerator 14 that functions as a cooling system for the polarizer system is also included and can be selected from a number of refrigerators (cold-heads or cryo-coolers) that are known and are commonly used on MRI magnets. The refrigerator 14 is positioned, at least in part, externally from vacuum chamber 12. Such a configuration allows any heat generated by the refrigerator 14 to be exhausted in the ambient environment rather than into the interior of vacuum chamber 12.
In one embodiment, refrigerator 14 is a closed cycle refrigerator capable of providing low temperature environments below 10 K. A separate vacuum enclosure 18 is provided for the refrigerator 14. The refrigerator itself is mounted in a vertical orientation within a mobile sleeve 20 to allow for vertical movement of the refrigerator 14 therein. The refrigerator 14 is further characterized in being field serviceable. That is, the cryostat design is such that the refrigerator 14 can be switched off and removed for a time that will allow a service engineer to replace or service the refrigerator. The polarizer system 10 is immune to such a procedure and is configured to continue operation for a period of time while refrigerator is shut off.
Referring still to
The samples 22 are introduced into the polarizer system 10 by way of a sample path 30 that passes through an ante chamber 32 (i.e., air lock). The purpose of the ante chamber 32 is to prevent contamination of the sample path 30 during introduction of the samples 22 and also to eliminate the need of breaking the vacuum on the sample path 30. In existing polarizer systems in the art, the sample path is pressurized to atmospheric pressure with helium gas; however, this is a major limitation of existing polarizers since bringing the sample path pressure to atmospheric pressure constitutes a significant heat load to the liquid helium bath and also transiently raises the temperature of the bath, i.e. reduces the throughput. In one embodiment of the present invention, the ante chamber 32 is isolated from vacuum chamber 12 by a gate valve 34 and from the atmosphere by a sealing cap 36. The ante chamber 32 can then, once the sample 22 has been introduced, be evacuated and flushed with helium gas in several cycles to eliminate and evacuate any air (and moisture). Thus, ante chamber 32 reduces the heat load to the liquid helium bath 26. The specific design of the ante chamber 32 will vary based on the geometry of the sample 22 and can be designed accordingly in a way known to one skilled in the art.
Referring also now to
The sample path 30 can also be equipped with a means of providing heat to the sample during a dissolution process or a means to mechanically agitate the sample during the dissolution. In one embodiment, once the sample 22 has been hyperpolarized to a desired state, the sample is dissolved by way of a heated solvent flowing thru sample 22 and is removed from the polarizer system 10 via the sample path 30 to a desired location/user. Referring now to
Referring again to
Referring now to
The need for liquid helium within holding container 44 is optional and will depend on the design of the microwave irradiation system, the sample properties, and the thermal contact to the sample 22. Rather that being filled with liquid helium, it is also envisioned that holding container 44 be filled with helium gas. The use of helium gas within holding container 44 for cooling sample 22 is desirable since this volume of helium may occasionally be evaporated and recondensed from, for example, a helium gas cylinder. Additionally, the helium gas can lead to improvement in the cryogenic performance of the polarizer system 10 by reducing the film flow from the helium bath if operated above the lambda point of helium.
To focus and confine the microwaves to sample 22, so as to provide for efficient polarization thereof, the holding container 44 contains a microwave confining arrangement that includes a waveguide 48 and optionally a sample cup 50. The microwave confining arrangement is designed in a way to deliver the microwave energy (microwave magnetic field) required for the DNP process. For example, if the magnetic field for polarization is chosen in the range 1-20 T, the microwave field would be in the range 3-560 GHz for a g=2 paramagnetic agent. In the embodiment of waveguide 48 shown in
Referring still to
In one embodiment, a NMR coil 60 is also included in the overall structure of the holding container 44. The NMR coil 60 is optional, but provides a means of measuring the nuclear polarization during and after the DNP polarization process by producing RF pulses that measure the polarization level of the sample 22. A number of arrangements for an NMR coil 60 are known in the art, and in a preferred embodiment, the NMR coil 60 is positioned outside the microwave confining arrangement. The NMR coil 60 can be a saddle coil, Helmholz coil, birdcage coil, or any other known design. The NMR coil 60 is connected to the outside of vacuum chamber 12 by, for example, a coaxial cable 62 or other suitable radio frequency cabling. In one embodiment, the NMR coil 60 is positioned inside of the holding container 44, although it is envisioned that NMR coil 60 could also be positioned outside of the holding container 44. The walls of the holding container 44 can be slit in such a way as to minimize losses and ensure radio frequency penetration. That is, the holding container 44 could, in part, be formed of copper and slit as desired to allow RF signals to penetrate therethrough and include a plastic inner shell 64 to provide a sealed holding container 44. To also allow the RF signals to penetrate into the sample 22, the thickness of the sample cup 50 walls is kept within a desired range such that the RF waves are not severely attenuated by the metallic sample cup.
Referring now to
Referring again to
The magnet 28 can favorably be operated sub-atmospheric to minimize the heat load to the refrigerator 14 from the magnet. If the magnet 28 is operated sub-atmospheric, a protective buffer helium volume can be added to any safety exhaust ports on the polarizer system 10 to prevent ingression of air and contamination of the magnet or sorption pump.
The magnet 28 is designed such as to provide a high magnetic fringe field region away from the very low temperature container 24. This high field region, e.g. 1-25 T or more, for example 5 T, is required in many instances during the dissolution of the sample 22. That is, as the dissolved sample is transferred out from container 24 via the sample path 30 and outside the volume of the vacuum chamber 12, a fringe magnetic field is desirable to maintain the hyperpolarized state of the sample 22. Furthermore, the magnet 28 can be designed in way that the fringe field is axially contained via active or passive shielding. Along the sample path 30, the magnetic field is preferably high, at least to an extent that the relaxation of the sample polarization is minimized at all steps of the dissolution process. Depending on the properties of the sample 22, this fringe magnetic field can be adjusted in intensity and coverage area as needed.
The magnet 28 and cryostat are also designed in such a way as to minimize or tolerate the interaction with an imaging magnet (not shown). In some circumstances, it is preferable to position the polarizer system 10 as close as possible to a magnetic resonance (MR) system (not shown) and the imaging magnet contained therein. In such an arrangement, magnetic field homogeneity and magnetic forces need to be carefully controlled on both magnets in order to minimize interference of the two magnetic fields and maintain homogeneity of the MR imaging field.
Referring still to
To achieve this reduction in pressure on liquid helium bath 26, sorption pump 46 is fluidly connected to container 24 by way of a pumping line 76. Sorption pump 46 is configured to lower pressure in container 24 by adsorbing the gas that evaporates from liquid helium bath 26. Sorption pump 46 operates in this sorption mode (i.e., polarization/pumping phase) when the pump is lowered to a cryogenic temperature. That is, when sorption pump 46 is cooled to a temperature of ˜10 K or below, helium gas will evaporate from liquid helium bath 26 and be adsorbed by sorption pump 46 forming a monolayer or two on a sorbent material therein.
As shown in
Continuing to refer to
As
Advantages of the system and apparatus, depicted in
Upon completion of a desired polarizing, or sorption pumping, phase in which samples 22 have been polarized, sorption pump 46 can be switched to condensing mode (i.e., reheating/desorption phase) to allow for the helium molecules adsorbed in sorbent material 80 to recondense and transfer back to container 24 to refill the liquid helium bath 26. Referring still to
As mentioned above, helium gas molecules that had previously been vaporized are allowed to recondense in the condensing/desorption phase. This recondensing is achieved by way of a condenser 88 (e.g., also referred to as helium condenser, container condenser, and/or second condenser herein) that is connected to sorption pump by way of pumping line 76. Helium gas released from sorbent material 80 during the desorption phase exits sorption pump 46 by way of the pumping line 76 and is carried to helium condenser 88. Helium condenser 88 functions to cool the helium gas to a temperature necessary to place the helium in a liquid state. Once the helium has been recondensed into a liquid state, it re-enters container 24 and liquid helium bath 26 is refilled. Helium condenser 88 is cooled by refrigerator 14 through connection thereto formed by common thermal bus 90. As shown in
In the first mode (i.e., condensing/desorption) of operation, the sorption pump 46 is directly and aggressively heated with the heater 86 adjoined thereto. This heating enables a rapid temperature rise in the large sorbent mass (e.g., >5 kg) in the sorption pump 46 and a release of large quantities of helium gas. The released helium gas is cooled and liquefied at condenser 88. The warm gas from the sorption pump 46 heats the thermal bus 72, 90 and effectively isolates the magnet vessel 70 due to a thermal diode “effect” experience at the magnet condenser 74. Thus, the heat related to the condensation of helium gas from the sorption pump 46 can be wholly and efficiently directed to the refrigerator 14 without negatively impacting the magnet 28.
Referring now to both
In the first mode (desorption/condense), shown to begin at 8:00 pm in this example, the thermal switch 84 is opened to enable the sorption pump 46 to be heated while minimizing the impact on the remaining components of the apparatus 10. With the thermal switch 84 effectively isolating the sorption pump 46 from the remainder of the system 10, the cooling power of the refrigerator 14 shared on the thermal bus 72, 90 by the magnet condenser 74 and helium condenser 88. Helium gas adsorbed in the sorption pump 46 is liberated and transported through the pumping line 76 to the condenser 88, resulting in the temperature of the thermal bus 72, 90 to rise. The rise in temperature at the thermal bus 72, 90 causes helium gas in the magnet vessel 70 and condenser 74 to stratify and effectively isolate the magnets vessel 70 from the remainder of the apparatus 10. At this point the majority of the cooling power of the refrigerator 14 is directed to the helium condenser 88 enabling the rapid and efficient condensation of helium gas to liquid, which is collected in the container 24. Through this procedure greater than 3 L of liquid helium can be collected in the container 24 during a 10 hour condensation period.
In order to cool the sorbent material 80, during the cooling phase, as described above, cooling fins 82 are attached to a thermal switch 84 that connects and disconnects sorption pump 46 from refrigerator 14 according to operator commands. Referring back to
In the second mode of operation (i.e., cooling), upon completion of the condensation of helium gas from sorption pump 46, heater element 86 is turned off and the sorption pump 46 is cooled by closing thermal switch 84, thereby creating a thermal linkage between the sorption pump 46, the thermal bus 72, 90, and refrigerator 14. During operation of the second mode, both condensers 74, 88 experience the thermal diode “effect” and isolate the magnet 28 and helium vessel 24 from the thermal bus 72, 90. This isolation of the magnet 28, in particular, allows the thermal bus 72, 90 to thereby achieve temperature greater than about 20K without impacting or affecting the magnet 28 and its temperature. In this manner, the higher temperatures achieved by the thermal bus 72, 90 allows the refrigerator 14 to achieve greater efficiency (e.g., 10×), thereby accelerating the rate of heat extraction from the heat pump 46.
The sorption pump 46 and connected pumping line 76 are designed to create a high pumping capacity. This high pumping capacity is needed to obtain a low base temperature in the liquid helium bath 26 in a reasonable time. Upon adsorption of a sufficient number of molecules to reduce the temperature of liquid helium bath 26 to a desired temperature for hyperpolarization of the sample 22, the sorption pump 46 is configured to maintain the low temperature of the liquid helium bath 26 for an extended time during which hyperpolarization can occur. The exact capacity of the sorption pump 46 to absorb helium and the volume of liquid helium in bath 26 can be designed and optimized to give the desired hold time of the low temperature for hyperpolarization.
In the third mode of operation (i.e., polarizing), the helium container or vessel 24 and sorption pump 46 are cold relative to the magnet 28, thereby eliminating any thermal diode “effect” from the condenser 74. This allows for the effective cooling of the magnet 28.
The functioning of the polarizer system 10 as a closed system operating in a cyclical thermal cycle provides for an efficient system for hyperpolarizing the sample 22. Additionally, the amount of liquid helium consumed during hyperpolarization is reduced essentially to zero because of the sorption pump 46 and condenser 88 arrangement, thus reducing maintenance on the polarizer system 10 as no liquid cryogens need to be filled and no mechanical pumps need to be serviced.
The polarizer system 10 heretofore described includes an adsorption pump 46 (i.e., sorption pump). While adsorption pumps have been used in a number of cryogenic applications, sorption pump 46 provides the unique benefits of having a very high adsorption capacity that translates into a high pumping capacity and long hold time. The polarizer system 10 also provides a single common refrigerator 14 that is configured to cool both the superconducting magnet 28 and the sorption pump 46. The superconducting magnet cryogenic system (i.e., refrigerator 14 and liquid helium contained in magnet vessel 70) is designed in such a way to be insensitive to the thermal cycle of sorption pump 46. The sorption pump 46 is capable of reaching temperatures well below any currently available refrigerator. While the embodiment of polarizer system 10 described above implements sorption pump 46, it is also envisioned that a refrigerator with sufficient capacity and base temperature can provide an environment having cryogenic temperatures in the range of 1.5 K that are suitable for hyperpolarization, such as an Adiabatic Demagnetization Refrigerator (ADR), which has also been successfully operated in low temperature physics applications.
In this manner, the system 10 intentionally isolates the magnet vessel 70 (and magnet 28) during cooling of the sorption pump 46 or its emitted gas. The system 10 exploits the large thermal mass of the magnet 28 so as to enable the magnet 28 to “ride” through a period when the magnet 28 is not receiving any supplemental cooling from the refrigerator 14. This intentional isolation allows the refrigerator 14 and its limited cooling power to be more efficiently utilized. The magnet 28 is thereby “insensitive” to the thermal cycle of the sorption pump 46, which ultimately enables the system 10 to operate more optimally in practical uses, including clinical applications.
Together
While polarizer system 10 has been described above as a self-contained system, it is also envisioned that the system be integrated with a MR imaging system. In such a configuration, an MR magnet functions to create the fringe magnetic field. With some local optimization of the strength and homogeneity of this fringe field, a sufficient DNP polarizing field needed for hyperpolarization of the 13C1-pyruvate sample can be created. Additionally, a helium reservoir of the MR imaging system used to cool the imaging magnet could also be used to provide liquid helium to the container surrounding the sample to be polarized. One implementation would be to connect the main helium reservoir to the container/sample space of the polarizer system via a capillary with a needle valve and controlling inflow of liquid helium to the container by way of the valve. The integration of the polarizer system with a MR imaging system would lead to a more compact and cheaper overall design.
As discussed earlier with regard to the stand alone polarizer system, it is often desirable to lower the temperature of the sample during polarization beyond the boiling point of helium at atmospheric pressure (4.2 K) in order to achieve high nuclear polarization of the sample. To reach these lower temperatures, the sample space (containing a bath of liquid helium) may be pumped on constantly by a sorption pump, which will result in a reduction of the helium's vapour pressure and consequently in a lower operating temperature. In light of the integration of the polarization system and the MRI imaging system, it is favourable to re-circulate the cold helium gas that is pumped out of the sample space to add to the cooling effect of the MR imaging magnet to provide additional cooling capacity (resulting in a longer helium hold time and obliterating the implementation of a liquid nitrogen reservoir) and to have an advantageous effect on cryogenic hold-time.
In general, the use of the MR imaging magnet for hyperpolarization would facilitate maintenance, as liquid helium re-filling would be performed on only the one integrated system rather than at different times for the two separate magnets. The integrated system would also take advantage of the existing cryogenic safety features of the MR scanner and make use of MR scanner electronics to monitor the increasing NMR signal from the sample while the polarization process is on-going.
Therefore, according to one embodiment of the present invention, an apparatus comprises a cooling container containing a cryogenic refrigerant therein, configured to hyperpolarize a plurality of samples therein; a refrigeration system comprising: a refrigerator; and a helium condenser, wherein the helium condenser is separate and positioned exterior to and apart from the cooling container; a sorption pump connected to the cooling container, wherein the sorption pump is separate and spaced apart from the cooling container; a thermal switch configured to connect and disconnect the refrigeration system from the sorption pump; a heater disposed adjoining the sorption pump, configured to heat the sorption pump and promote molecular desorption therein; a single magnetic field producing device in thermal communication with the refrigeration system, wherein the single magnetic field producing device is configured to maintain a selected magnetic field in the apparatus, wherein the single magnet field producing device comprises: a superconducting magnet having a bore therethrough positioned about the cooling container; a magnet vessel to enclose the superconducting magnet, the magnet containing liquid cryogen therein to cool the superconducting magnet; and a magnet condenser configured to recondense helium gas that evaporates due to a heat load to the superconducting magnet, wherein the superconducting magnet is configured to produce a primary magnetic field region about the cooling container for hyperpolarization of the plurality of samples and a secondary magnetic field region offset from the primary magnetic field region that extends axially out from the superconducting magnet, wherein the superconducting magnet is further configured to operate without quench or loss of liquid helium when disconnected from the refrigeration system; and at least one thermal bus connecting the refrigeration system, the helium condenser, the magnet condenser, and the thermal switch, further wherein the apparatus comprises a closed system.
In accordance with another embodiment of the present invention, a polarizing subsystem comprises: a container having a liquid helium bath configured to receive a material to be polarized; a sorption pump to reduce a pressure in the container, thereby to vaporize a portion of the liquid helium bath, the sorption pump comprising: a sorb can configured separate, spaced apart, and exterior to the container; a cooling system comprising: a magnet condenser configured separate, spaced apart, and exterior to the container, configured to recondense liquid helium boiled off therefrom and cool the sorption pump and promote molecular adsorption therein; a thermally conductive link that selectively connects the sorption pump and the cooling system to provide selective cooling to the sorption pump; a heater disposed adjoining the sorption pump, the heater configured to heat the sorption pump and promote molecular desorption therein; a single magnetic field producing device configured to maintain a selected magnetic field for polarizing the material in the apparatus, wherein the single magnetic field producing device is cooled by the cooling system, wherein the polarizer system operates in a closed cyclical thermal cycle alternating between a polarizing phase and a reheating phase based on the thermally conductive link of the sorption pump to the cooling system.
In accordance with yet another embodiment of the present invention, a method for producing a hyperpolarized material comprises: placing a material sample in a vessel containing a liquid helium bath; reducing a temperature of the liquid helium bath with a sorption pump and a refrigeration system, wherein the sorption pump comprises: a sorb can configured separate from and exterior to and spaced apart from the vessel, wherein the refrigeration system comprises: a helium condenser configured separate from and exterior to and spaced apart from the vessel; refilling the liquid helium bath by heating the sorption pump with a heater, the heater being disposed adjoining the sorption pump; positioning a single magnetic field producing device adjacent the vessel, wherein the single magnetic field producing device is configured to product a high homogeneity magnetic field and a fringe magnetic field offset from the high homogeneity field; and polarizing the material sample when the liquid helium bath has been sufficiently cooled by the single magnetic field producing device.
In accordance with yet another embodiment of the present invention, a polarizer system comprises: a refrigerator; a magnet condenser; a helium condenser; a thermal bus permanently linking the refrigerator, the magnet condenser, and the helium condenser; a sorption pump selectively linked through a thermal switch to the thermal bus; a heater adjoining the sorption pump; a container containing a cryogenic refrigerant therein, configured to receive a plurality of samples for polarizing therein; a magnetic field producing device in a magnet vessel surrounding the container; wherein the polarizing system is further configured to operate in three separate modes, wherein: a first mode comprises: heating the sorption pump with the heater, thereby releasing helium gas to be cooled and liquefied by the helium condenser, wherein the released helium gas heats the thermal bus, thereby isolating the magnet vessel due to a thermal diode effect at the magnet condenser; a second mode comprises: upon completion of condensation of helium from the sorption pump, turning off the heater and cooling the sorption pump by closing the thermal switch, thereby creating a thermal linkage of the sorption pump, the thermal bus and the refrigerator, and thermally isolating the magnetic field producing device from the thermal bus; and, a third mode comprises: cooling the magnetic field producing device, thereby eliminating a thermal diode effect of the magnet condenser.
The present invention has been described in terms of the preferred embodiment, and it is recognized that equivalents, alternatives, and modifications, aside from those expressly stated, are possible and within the scope of the appending claims.
This Continuation-In-Part (C.I.P.) application claims the benefit of the Apr. 2, 2007 filing date of U.S. application Ser. No. 11/695,411 (Entitled: METHOD AND APPARATUS TO HYPERPOLARIZE MATERIALS FOR ENHANCED MR TECHNIQUES, attorney docket no. 205265-1). The aforementioned application is incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11695411 | Apr 2007 | US |
| Child | 14103294 | US |
