Hyperpolarized media transport vessel

A system and method for transporting a hyperpolarized substance is disclosed. A transport vessel for transporting such a hyperpolarized substance includes a vessel housing, a chamber formed within the vessel housing that is configured to receive a container holding a hyperpolarized substance, and an electromagnet configured to generate a magnetic containment field about the chamber when a current is supplied thereto, the magnetic containment field comprising a homogeneous magnetic field. The transport vessel also includes a non-magnetic power source to supply the current to the electromagnet and a control circuit configured to selectively interrupt the supply of current to the electromagnet so as to control generation of the magnetic containment field, with the transport vessel being magnetically inert when the supply of current to the electromagnet is interrupted by the control circuit.

BACKGROUND OF THE INVENTION

Embodiments of the invention relate generally to a hyperpolarized media for use in magnetic resonance imaging (MRI) and nuclear magnetic resonance (NMR) spectroscopy and, more particularly, to a vessel for transporting such a hyperpolarized media from a production source to an imaging system.

MRI and NMR spectroscopy are techniques that exploit the magnetic properties of certain atomic nuclei. With particular regard to MRI, a substance such as human tissue is subjected to a uniform magnetic field (polarizing field B0), causing the individual magnetic moments of the spins in the tissue to attempt to align with this polarizing field, but precess about it in random order at their characteristic Larmor frequency. If the substance, or tissue, is subjected to a magnetic field (excitation field B1) which is in the x-y plane and which frequency is near the Larmor frequency, the net aligned moment, or “longitudinal magnetization”, MZ, may be rotated, or “tipped”, into the x-y plane to produce a net transverse magnetic moment Mt. A signal is generated by the excited spins after the excitation signal B1is terminated and this signal may be received and processed to form an image.

When utilizing these signals to produce images, magnetic field gradients (Gx, Gy, and Gz) are employed. Typically, the region to be imaged is scanned by a sequence of measurement cycles in which these gradients vary according to the particular localization method being used. The resulting set of received NMR signals are digitized and processed to reconstruct the image using one of many well known reconstruction techniques. It is desirable that the imaging process, from data acquisition to reconstruction, be performed as quickly as possible for improved patient comfort and throughput.

One drawback to MRI and NMR spectroscopy is that they lack sensitivity due to the normally very low polarization of the nuclear spins of the samples used and/or substances being imaged. A number of techniques exist to improve the polarization of nuclear spins in the solid phase. These techniques are known as hyperpolarization techniques and lead to an increase in sensitivity. In hyperpolarization techniques, a sample of an imaging agent, for example13C Pyruvate or another similar polarized metabolic imaging agent, is introduced or injected into the subject being imaged. As used herein, the term “polarize” refers to the modification of the magnetic properties of a material for further use in MRI. Further, as used herein, the term “hyperpolarized” refers to polarization to a level over that found at room temperature and 1 T.

However, while hyperpolarized media is highly effective in improving the polarization of nuclear spins for MRI and NMR spectroscopy, it is recognized that the magnetic polarization of the hyperpolarized media has a short lifetime—with relaxation occurring in a matter of seconds to minutes, therefore requiring the media to be used in the MRI as soon as possible after hyperpolarization. This short lifetime of the magnetic polarization of the hyperpolarized media can be problematic since the polarized sample is often transported to the MRI unit from a hyperpolarizing apparatus that is located outside of the MRI imaging suite, requiring an operator to physically transport the hyperpolarized media from the hyperpolarizer to the MRI unit.

The short lifetime of the hyperpolarized media can be further negatively affected if the hyperpolarized media is not maintained in a suitable magnetic field. That is, movement of the media through a zero magnetic field or low background magnetic field below 1-2 Gauss (e.g., the background magnetic field generated by the MRI unit) can further shorten the lifetime of the hyperpolarized media. In order to address this problem, one solution has been to provide a specially designed vessel for transporting the hyperpolarized media between the hyperpolarizing apparatus and the MRI unit.

In one prior art vessel, a hollow transport vessel was designed with permanent magnetic material arranged inside designed to generate a suitable and stable background magnetic field for transporting the hyperpolarized media from the hyperpolarizer apparatus to the MRI unit, so as to maintain the hyperpolarized state of the media. However, such a permanent magnet transport vessel has several drawbacks, including: an inability to control the strength of the magnetic field generated by the vessel, significant inhomogeneity of the background magnetic field created inside the vessel, and the inability to turn the magnetic field off—which can cause the device to be interact with the MRI magnet with great force when brought in the vicinity of the MRI unit, such as by being attracted to or expelled from the magnet or being caused to twist/torque in the presence of the magnet.

Therefore, it is desirable to provide a transport solution that can safely and efficiently provide a suitable background magnetic field that is stable (homogenous magnetic field around hyperpolarized media) and preserves the lifetime of the hyperpolarized media. It would further be desirable for such a transport solution to be made of non-magnetic materials and equipped with a mechanism that enables selective generation of such a background magnetic field, so as to provide for disengaging of the magnetic field when necessary.

BRIEF DESCRIPTION OF THE INVENTION

In accordance with one aspect of the invention, a transport vessel for transporting a hyperpolarized substance includes a vessel housing, a chamber formed within the vessel housing that is configured to receive a container holding a hyperpolarized substance, and an electromagnet configured to generate a magnetic containment field about the chamber when a current is supplied thereto, the magnetic containment field comprising a homogeneous magnetic field. The transport vessel also includes a non-magnetic power source to supply the current to the electromagnet and a control circuit configured to selectively interrupt the supply of current to the electromagnet so as to control generation of the magnetic containment field, with the transport vessel being magnetically inert when the supply of current to the electromagnet is interrupted by the control circuit.

In accordance with another aspect of the invention, a device for transporting a hyperpolarized substance includes a vessel housing, a chamber formed within the vessel housing that is configured to receive a container holding a hyperpolarized substance, and an electromagnet configured to generate a magnetic containment field about the chamber when a current is supplied thereto, the magnetic containment field comprising a homogeneous field about the container. The device also includes a non-magnetic power source to supply the current to the electromagnet and a safety circuit configured to selectively interrupt the supply of current to the electromagnet in an automated fashion so as to control generation of the magnetic containment field, with the safety circuit further including a pressure activated safety switch configured to interrupt the supply of current to the electromagnet when a pressure applied to the safety switch is less than a threshold pressure value.

In accordance with yet another aspect of the invention, a method for transporting hyperpolarized substance includes securing a container holding a hyperpolarized substance within chamber formed in a transport vessel and generating a magnetic containment field about the chamber and about the container by way of an electromagnet of the transport vessel, the electromagnet configured to generate a homogeneous magnetic containment field having a controlled polarity that is free of switching between positive and negative charges so as to prolong a hyperpolarized state of the hyperpolarized substance. The method also includes selectively terminating the magnetic containment field in an automated fashion based upon a sensing of one or more parameters exceeding or falling below a pre-determined threshold value, the magnetic containment field being selectively terminated by way of a safety circuit of the transport vessel.

DETAILED DESCRIPTION

Embodiments of the invention provide a transport device or vessel that is configured to preserve hyperpolarization of a media when transporting the media in a hyperpolarized state, such as between a hyperpolarizer device and a magnetic resonance imaging (MRI) system, and provide for safe use of the vessel in the vicinity of the MRI system. While the transport vessel is described below as being used to transport a hyperpolarized media to an MRI system for use in an image acquisition performed thereby, it is recognized that the hyperpolarized media could be used in conjunction with other imaging techniques in which use of a hyperpolarized media is desired, such as nuclear magnetic resonance (NMR) spectroscopy for example.

Referring toFIG. 1, the major components of a magnetic resonance imaging (MRI) system10incorporating an embodiment of the invention are shown. The operation of the system is controlled for certain functions from an operator console12which in this example includes a keyboard or other input device13, a control panel14, and a display screen16. The console12communicates through a link18with a separate computer system20that enables an operator to control the production and display of images on the display screen16. The computer system20includes a number of modules which communicate with each other through a backplane20a. These modules include an image processor module22, a CPU module24and a memory module26, known in the art as a frame buffer for storing image data arrays. The computer system20communicates with a separate system control32through a high speed serial link34. The input device13can include a mouse, joystick, keyboard, track ball, touch activated screen, light wand, voice control, card reader, push-button, or any similar or equivalent input device, and may be used for interactive geometry prescription.

The system control32includes a set of modules connected together by a backplane32a. These include a CPU module36and a pulse generator module38which connects to the operator console12through a serial link40. It is through link40that the system control32receives commands from the operator to indicate the scan sequence that is to be performed. The pulse generator module38operates the system components to carry out the desired scan sequence and produces data which indicates the timing, strength and shape of the RF pulses produced, and the timing and length of the data acquisition window. The pulse generator module38connects to a set of gradient amplifiers42, to indicate the timing and shape of the gradient pulses that are produced during the scan. The pulse generator module38can also receive patient data from a physiological acquisition controller44that receives signals from a number of different sensors connected to the patient, such as ECG signals from electrodes attached to the patient. And finally, the pulse generator module38connects to a scan room interface circuit46which receives signals from various sensors associated with the condition of the patient and the magnet system. It is also through the scan room interface circuit46that a patient positioning system48receives commands to move the patient to the desired position for the scan.

The gradient waveforms produced by the pulse generator module38are applied to the gradient amplifier system42having Gx, Gy, and Gz amplifiers. Each gradient amplifier excites a corresponding physical gradient coil in a gradient coil assembly generally designated50to produce the magnetic field gradients used for spatially encoding acquired signals. The gradient coil assembly50forms part of a resonance assembly52which includes a polarizing magnet54and a whole-body RF coil56. A transceiver module58in the system control32produces pulses which are amplified by an RF amplifier60and coupled to the RF coil56by a transmit/receive switch62. The resulting signals emitted by the excited nuclei in the patient may be sensed by the same RF coil56and coupled through the transmit/receive switch62to a preamplifier64. The amplified MR signals are demodulated, filtered, and digitized in the receiver section of the transceiver58. The transmit/receive switch62is controlled by a signal from the pulse generator module38to electrically connect the RF amplifier60to the coil56during the transmit mode and to connect the preamplifier64to the coil56during the receive mode. The transmit/receive switch62can also enable a separate RF coil (for example, a surface coil) to be used in either the transmit or receive mode.

The MR signals picked up by the RF coil56are digitized by the transceiver module58and transferred to a memory module66in the system control32. A scan is complete when an array of raw k-space data has been acquired in the memory module66. This raw k-space data is rearranged into separate k-space data arrays for each image to be reconstructed, and each of these is input to an array processor68which operates to Fourier transform the data into an array of image data. This image data is conveyed through the serial link34to the computer system20where it is stored in memory. In response to commands received from the operator console12or as otherwise directed by the system software, this image data may be archived in long term storage or it may be further processed by the image processor22and conveyed to the operator console12and presented on the display16.

In using the MRI system10in acquiring MR image data, a hyperpolarized media or substance may be employed to improve the polarization of nuclear spins in the solid phase, so as to increase the sensitivity of signal acquisition and provide better contrast in images that are reconstructed, with additional functionality being provided in/on the MRI system10to enable signal acquisition from hydrogen nuclei and/or nuclei other than hydrogen (as might be encountered in spectroscopy employing a hyperpolarized media or substance). The hyperpolarized substance, such as13C Pyruvate or another similar polarized metabolic imaging agent is introduced or injected into the subject being imaged. It is recognized that the magnetic polarization of the hyperpolarized media has a short lifetime—with relaxation occurring in a matter of seconds to minutes, therefore requiring the media to be used for MR image acquisition as soon as possible after hyperpolarization. As such, it is desirable to provide a vessel for transporting the hyperpolarized substance from a hyperpolarizing apparatus at which the substance is polarized to the MRI system for providing to the subject. The transport vessel maintains the hyperpolarized media in a suitable magnetic field so as to prolong the magnetic polarization of the hyperpolarized substance. It is also desirable for such a transport vessel to made of non-magnetic materials and equipped with a mechanism that enables selective generation of such a background magnetic field, so as to prevent interaction between the vessel and the MRI magnet that could result in a twisting/torquing of the vessel in the presence of the magnet—thereby providing for safe use of the vessel.

Referring toFIGS. 2 and 3, a hyperpolarized media transport vessel100is shown according to an exemplary embodiment of the invention. The vessel100includes a non-magnetic vessel housing102that is constructed to form and surround a hollow interior or chamber104. The chamber104is sized and shaped to receive a container106therein that holds a hyperpolarized media108, such as an infusion syringe or flask for example, with the chamber104receiving the container106therein and providing suitable protection to the container for transport—such as by keeping the container106stationary within chamber104. According to one embodiment, a non-magnetic filler material (not shown) can be employed to define the chamber104within housing102, to snugly receive the container106therein and provide for safe/secure transport thereof.

The vessel housing102is compact and light enough to allow the operator to transport vessel100by hand, and may be any of a number of shapes or constructions, such as cylindrical, rectangular, or another functionally equivalent configuration. The vessel housing is composed of a suitable non-magnetic and medically acceptable material, such as Polyethylene (PE) for example, that provides protection to the container106while being inert to magnetic fields that may be present about the vessel100—e.g., those generated by an MRI magnet—such that the vessel100does not interact with the magnetic field generated thereby (i.e., being attracted to/expelled from a magnetic field and/or being twisted torque by the magnetic field).

As shown inFIG. 2, the vessel housing102includes an opening110formed therein to provide for insertion of the container106into the vessel100. According to one embodiment of the invention, a cover111is optionally provided that is positionable in the opening110to enclose the container within chamber104when it is desired to transport the container with vessel100. While not shown inFIGS. 2 and 3, it is contemplated that vessel100may also include an outer covering (not shown) formed about the housing102in order to protect vessel100and to facilitate convenient and ergonomic transport.

As shown inFIG. 2, and in the block schematic diagram ofFIG. 4, an electromagnet112is included in vessel100and formed on the housing102such that the electromagnet generally surrounds the chamber104—with the electromagnet112being configured to generate a suitable and stable background magnetic field for transporting the hyperpolarized media within vessel100, i.e., a magnetic containment field114that surrounds the chamber104, so as to maintain the hyperpolarized state of the media. The electromagnet112can be any device which creates a magnetic field from electrical input. In the embodiment inFIG. 2, electromagnet112is in the form of a single solenoid coil formed from a plurality of windings of copper wire116that are wrapped around vessel housing102so as to encircle the chamber104, with the solenoid112being housed within an electrically insulating outer cover (not shown) of the vessel100so as to be protected from the ambient environment. In operation, as shown inFIG. 3, the electromagnet112generates a magnetic containment field114about chamber104, with the magnetic containment field114including a homogenous magnetic field section115that surrounds hyperpolarized media108in container106—as indicated by the parallel magnetic field lines114within electromagnet112. The homogenous magnetic field section115of magnetic containment field114has a controlled polarity that is free of switching between positive and negative charges.

While electromagnet112is described above as being in the form of a single solenoid coil, it is recognized that other coil configurations could be employed. That is, according to one embodiment of the invention, electromagnet112can be formed of multiple coils/coil portions117—such as shown in an embodiment of the vessel illustrated inFIGS. 5 and 6—that are each individually controllable (e.g., with each with individual current control circuits), so as to provide for effecting magnetic transport fields of varying qualities in multiple dimensions. According to an exemplary embodiment, the coils/coil portions117are arranged so as to provide a 3-axis electromagnet, such as by winding two saddle-shaped coils117aon cylinder(s) concentric to the solenoid coil117band with their field axes oriented perpendicular to each other, as illustrated inFIG. 6.

As shown inFIG. 4, vessel100also includes a power source118and a power control120to selectively provide power to the electromagnet112. In one embodiment, power supply118is a non-magnetic battery, such as a lithium-ion polymer (LiPo) single cell battery, but it is recognized that the power supply118may be any non-magnetic power source that does not interact with a surrounding magnetic field, such as one generated by an MRI magnet. It is also contemplated power supply118is large enough to provide sufficient power to electromagnet112for at least one use, and preferably multiple uses, for transporting a hyperpolarized media from its production source to its location for use in an MR image acquisition. The power control120controls the amount of current flowing from power source118to electromagnet112, thereby allowing an adjustment of a strength of the magnetic containment field114generated by the electromagnet112, such as between a value of 0 and 100 Gauss. The power control120advantageously provides for dynamic adjustment of the magnetic containment field114, such that the hyperpolarization of the hyperpolarized media being transported can be better preserved, with adjustment of a strength of the field114accounting for variation in system components (such as power source118), or to compensate for background magnetic field variation in the environment. It is contemplated power control120could be as simple as a basic rheostat, or as intricate as a separate control system controlled by a remote operator. Additionally, in an embodiment where electromagnet112is formed from multiple, individually addressable coils/coil portions117, such as shown inFIG. 5, power control120may include a number of individual current control circuits so as to enable the supplying of a desired current to each of the coils117to effect magnetic transport fields of varying qualities in multiple dimensions. In addition, individual current control circuits may be configured to individually address separate and distinct coils to provide active shielding around the electromagnet112. That is, separate coils/coil portions117may be configured to provide additional cancellation of the effects of ambient magnetic fields on electromagnet112, further protecting homogenous region115and the hyperpolarized media108contained therein and reducing the interaction between the electromagnet112and the ambient magnetic fields generated by MR magnet54.

According to one embodiment, and in order to make an efficient transport device100, it is contemplated that the strength and homogeneity of the magnetic containment field114may be calibrated by positioning a magnetic field sensor122(hall effect), or a separate magnetic field sensor, inside chamber104and manipulating power control120to achieve the desired field strength. The transport field can be “locked” at a specific field strength based on active feedback provided by the magnetic field sensor122to the power/current control circuit120. This approach could be used to “shield” the hyperpolarized media from external fluctuating fields on the order of kilohertz and lower with an appropriately designed feedback circuit.

As further shown inFIG. 4, a control circuit124(i.e., “safety circuit”) is included in the vessel100that provides for selective operation thereof—with the control circuit124enabling selective interruption of the supply of current to the electromagnet112so as to control generation of the magnetic containment field. That is, it is recognized that disengaging/termination of the magnetic containment field is necessary for vessel100in order for the vessel to be brought into the vicinity of an MRI system (i.e., the magnet of the MRI system)—as continued generation of the magnetic containment field in the presence of an MRI system could cause the device to be twisted/torque responsive to the field generated by the MRI magnet when brought in the vicinity of the MRI system (i.e., as the electromagnet attempts to align its magnetic axis with the MRI magnet's field) thereby causing a person to lose hold of the vessel. According to the embodiment illustrated inFIG. 4, control circuit124includes a plurality of switches and sensor(s) that function to selectively interrupt the supply of current to the electromagnet112. Included in control circuit124is a manually activated power switch126. The manually activated power switch126is movable by an operator to provide for turning the electromagnet on and off as desired.

Control circuit124also includes a number of switches/sensors therein that provide for an “automatic” interruption of current to the electromagnet112under certain pre-determined conditions. Such automated features are highly desirable as additional safeguards, as they provide for disengaging/termination of the magnetic containment field114in situations where the operator forgets to terminate a supply of power to the electromagnet112(e.g., forgets to manually shut off power to electromagnet112by way of power switch126) or where some unforeseen event prevents the operator from terminating a supply of power to the electromagnet112.

As one safeguard for providing automatic interruption of current to the electromagnet112, control circuit124includes a pressure safety switch128that functions to selectively interrupt current flow. The pressure safety switch128is configured as a “deadman switch” that enables a flow of current from power source118to electromagnet112—so as to create magnetic containment field114—only when the operator is applying an amount of pressure to safety switch128that is greater than a minimum threshold pressure value. The threshold pressure value is the amount of force required to depress the safety switch128button, which creates a short across safety switch128in control circuit124, thus allowing current flow from power source118to electromagnet112, and creating electromagnetic containment field114. In the situation where the operator releases vessel100or an MRI magnet causes the vessel100to leave the operator's grasp (i.e., the MRI magnet attracts the vessel100and causes it to be pulled from the grasp of the operator), the pressure applied to safety switch128will be less than the threshold pressure value, causing a disconnect in control circuit124, thereby interrupting current flow between power source118and electromagnet112and consequently interrupting magnetic containment field114, ensuring magnetic containment field114will not further interact with any surrounding magnetic fields.

As another safeguard for providing automatic interruption of current to the electromagnet112, control circuit124includes a magnetic field sensor/current interruption circuit129that is composed of a magnetic field sensor130(with it being recognized that the sensor130may be separate from sensor122, as shown inFIG. 4, or the same sensor), a processor131, and a magnetic field safety switch132. The magnetic field sensor130detects the strength of an ambient magnetic field in an immediate area around vessel100, while processor131is operably coupled to magnetic field sensor130to receive an input regarding the ambient field strength. The processor131is programmed to cause magnetic field safety switch132to open when the ambient magnetic field strength is greater than a threshold value—with the threshold value being set in processor131by the operator. The threshold value is contemplated to be a maximum magnetic field strength that does not cause a potentially dangerous interaction between background magnetic fields and vessel100. In operation of vessel100, current is supplied to electromagnet112by power source118until magnetic field sensor130detects a background magnetic field greater than a threshold value, after which processor131causes magnetic field safety switch132to open, selectively interrupting current flow to electromagnet112, thereby interrupting magnetic containment field114. The circuit129thus ensures that magnetic containment field114does not interact with background magnetic fields above the threshold value, such as those background fields inherent around an MRI magnet, thereby preventing the transport vessel100from being expelled from or pulled toward the MRI magnet.

Therefore, according to one embodiment of the invention, a transport vessel for transporting a hyperpolarized substance includes a vessel housing, a chamber formed within the vessel housing that is configured to receive a container holding a hyperpolarized substance, and an electromagnet configured to generate a magnetic containment field about the chamber when a current is supplied thereto, the magnetic containment field comprising a homogeneous magnetic field. The transport vessel also includes a non-magnetic power source to supply the current to the electromagnet and a control circuit configured to selectively interrupt the supply of current to the electromagnet so as to control generation of the magnetic containment field, with the transport vessel being magnetically inert when the supply of current to the electromagnet is interrupted by the control circuit.

According to another embodiment of the invention, a device for transporting a hyperpolarized substance includes a vessel housing, a chamber formed within the vessel housing that is configured to receive a container holding a hyperpolarized substance, and an electromagnet configured to generate a magnetic containment field about the chamber when a current is supplied thereto, the magnetic containment field comprising a homogeneous field about the container. The device also includes a non-magnetic power source to supply the current to the electromagnet and a safety circuit configured to selectively interrupt the supply of current to the electromagnet in an automated fashion so as to control generation of the magnetic containment field, with the safety circuit further including a pressure activated safety switch configured to interrupt the supply of current to the electromagnet when a pressure applied to the safety switch is less than a threshold pressure value.

According to yet another embodiment of the invention, a method for transporting hyperpolarized substance includes securing a container holding a hyperpolarized substance within chamber formed in a transport vessel and generating a magnetic containment field about the chamber and about the container by way of an electromagnet of the transport vessel, the electromagnet configured to generate a homogeneous magnetic containment field having a controlled polarity that is free of switching between positive and negative charges so as to prolong a hyperpolarized state of the hyperpolarized substance. The method also includes selectively terminating the magnetic containment field in an automated fashion based upon a sensing of one or more parameters exceeding or falling below a pre-determined threshold value, the magnetic containment field being selectively terminated by way of a safety circuit of the transport vessel.