Abstract:
An apparatus and method for providing RF shielding for performing nuclear magnetic resonance (“NMR”) procedures, comprising a radio-opaque holder in combination with radio-opaque magnet components to form an RF shield around a patient undergoing an NMR procedure. In embodiments, a radio-opaque holder having a radio-opaque bottom portion and a radio-opaque canopy is adjoined to an NMR magnet having a radio-opaque cryostat and a radio-opaque service end cap to form an RF shield. A patient is placed on a patient support unit located in the holder bottom portion. The patient support unit, including the patient, is then inserted into the cavity of the NMR magnet and a canopy is placed on top of the bottom portion of the holder. An RF shield is thus created comprising the canopy, the bottom portion, the cryostat of the magnet, and an end cap on the service end of the magnet.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to nuclear magnetic resonance (“NMR”) procedures, such as magnetic resonance imaging (“MRI”), magnetic resonance angiography (“MRA”) and magnetic resonance spectroscopy (“MRS”). More specifically, the present invention relates to a system, method and apparatus for shielding against unwanted radio frequency signals when performing an NMR procedure. The invention is designed for clinical veterinary applications, but could be employed for any NMR application.  
           [0003]    2. Related Art  
           [0004]    NMR technology has provided physicians with the ability to view the inside of a human patient&#39;s body in order to form accurate diagnoses and prescribe proper treatments. Because NMR procedures rely on the detection of RF signals with low signal-to-noise ratios, NMR procedures are typically conducted in environments that are substantially free of unwanted RF signals. The usual manner by which a “clean” environment (that is, an environment substantially free of unwanted RF noise) is achieved is by shielding the room in which the NMR procedure takes place. This approach involves building a contiguous radio-opaque screen, known as a faraday cage, to encompass an entire room—including floors, ceilings, and walls. All openings into the room, such as windows, doors, and penetrations for power supply and other cables, are formed in a manner that does not impair the integrity of the RF shield.  
           [0005]    Doctors who practice veterinary medicine can benefit from the diagnostic capabilities of NMR technology. However, due to the cost associated with obtaining NMR equipment and providing a dedicated, RF-shielded room for the procedure, veterinarians typically are unable to offer NMR procedures to their patients. Accordingly, NMR procedures are not readily available to most non-human patients; indeed, pet owners wishing to have NMR procedures conducted on their pets normally have to pay to have their pets taken after business hours to hospitals or offices having NMR equipment for use with humans.  
           [0006]    Thus, there is a need for a cost-effective way to provide doctors who practice veterinary medicine with the ability to offer NMR procedures to their patients.  
         SUMMARY OF THE INVENTION  
         [0007]    Features and Advantages  
           [0008]    The following features characterize some, but not necessarily all, embodiments of the present invention.  
           [0009]    One feature of an embodiment of the present invention is that it reduces the cost of NMR procedures by eliminating the need for a dedicated, RF-shielded room for performing such procedures. By forming the RF shield around the patient and RF coils, as opposed to around the NMR room itself, embodiments of the present invention facilitate the use inside the NMR room of electronic equipment to support NMR procedures as well as of AC (rather than DC) lighting fixtures.  
           [0010]    Another feature of an embodiment of the present invention is that it enables the patient space to be climactically controlled, thus facilitating the maintenance of the patient&#39;s temperature.  
           [0011]    Another feature of an embodiment of the present invention is that it provides an improved support unit for holding a non-human patient during an NMR procedure.  
           [0012]    Another feature of an embodiment a support unit of the present invention is that it provides the ability to modify an RF coil configuration for an anesthetized patient to image different parts of the patient&#39;s body without moving the patient.  
           [0013]    Further features and advantages will become apparent following review of the detailed description set forth below or in the course of practicing the invention.  
         SUMMARY  
         [0014]    In summary, the invention comprises a radio-opaque holder for holding a patient support unit supporting a patient about to undergo an NMR procedure, and for providing, in conjunction with shielding provided by an NMR magnet, RF shielding for the procedure. In an embodiment, the patient support unit can be moved from the holder into the magnet when the holder adjoins the magnet. In embodiments, the holder may comprise a canopy and a bottom portion such that when the canopy is placed over the bottom portion, a radio-opaque enclosure—which may be substantially cylindrical in shape—is formed around the patient support unit. In an embodiment, the patient end of the holder is enclosed with radio-opaque material, for example as a result of the placement of the canopy on top of the bottom portion of the holder, or as a result of use of a separate patient end cap. In an embodiment, the magnet end of the holder is open, and is configured so that, when the holder is adjoined with the opening of the NMR magnet, the RF shielding associated with the magnet (“magnet-RF-shielding”) and RF shielding associated with the holder (“holder-RF-shielding”) combine to form a continuous RF shield.  
           [0015]    The holder may be formed to operate with existing NMR magnets, or specialized NMR magnets may be produced to operate together with the holder as a system. For a magnet whose construction provides sufficient RF shielding (as, for example, a superconducting magnet whose inner diameter comprises a cryostat made of radio-opaque material), the shield may be completed by the RF shield provided by the magnet itself combined with a radio-opaque service end cap that covers the service end of the magnet. In such embodiments, the result is a cylindrical RF shield fully encompassing the patient, which has a length of approximately the length of the cavity of the magnet, plus the length of the holder.  
           [0016]    The holder may comprise a base unit, which may enable the holder to be moved (for instance, by means of wheels or rollers) to adjoin the magnet in a manner that aligns the bottom portion of the holder with the bore of the magnet to facilitate insertion of the patient into the magnet cavity. The holder may be attachable to the magnet by means of a docking mechanism, for example.  
           [0017]    In embodiments, the bottom portion of the holder is designed to include within it a patient support unit, typically on a longitudinal track formed on the bottom portion of the holder that can be aligned with a similar horizontal track in the bore of the magnet. The alignment of the tracks facilitates movement of the patient support unit from the holder into the magnet for an NMR procedure.  
           [0018]    The patient support unit may be made of a material that slides well on the bottom portion of the holder as well as in the bore of the magnet. A suitable combination of materials is, for example, Teflon-coated fiberglass for the patient support unit, and Teflon-coated carbon fiber for the bottom portion of the holder and the bore of the magnet (which may be a cryostat). In embodiments, the patient support unit includes a bed that is configured to hold an animal, preferably in an inverted position. The bed may be formed substantially to match the curvature of the animal&#39;s spine, and different-sized and different-shaped beds (in some embodiments, on different patient support units) may be used to accommodate different sizes and shapes of animals. The patient support unit may include RF transmitter antennas and receiver antennas, such as RF coils, that provide RF energy used in the NMR procedure. In embodiments, the bed includes lower RF coils as well as connectors for upper RF coils for use forming, in conjunction with the lower RF coils, volume coils for imaging parts of the patient&#39;s body such as the head and abdomen. In embodiments, the RF coils are movable with respect to the bed, to facilitate imaging different parts of the patient&#39;s body.  
           [0019]    The patient support unit of the invention may be used in conjunction with the holder of the invention, in which case the holder-RE-shielding and the magnet-RF-shielding provide RF shielding for the NMR procedure. The patient support unit of the invention can also be used with holders that do not comprise RF shielding, or with NMR magnets that do not comprise RF shielding, as, for example, in cases where a faraday cage provides RF shielding for the NMR room.  
           [0020]    The invention also includes a method for performing an NMR procedure using the apparatus and system described above and in this specification.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]    [0021]FIG. 1 depicts an embodiment of a holder of the invention, including a canopy, as it relates to an NMR magnet during an NMR procedure.  
         [0022]    [0022]FIG. 1A provides an illustration of a service end cap attached to the service end of an NMR magnet.  
         [0023]    [0023]FIG. 1B depicts an embodiment of a holder of the invention, with the canopy removed, as it relates to an NMR magnet during an NMR procedure.  
         [0024]    [0024]FIG. 1C depicts an embodiment of a holder of the invention holding a patient support unit of the invention.  
         [0025]    [0025]FIG. 2 depicts the components that make up a patient support unit of an embodiment of the invention.  
         [0026]    [0026]FIG. 2A depicts an embodiment of a patient support unit of the invention.  
         [0027]    [0027]FIG. 2B depicts an embodiment of a patient support unit viewed from the patient end. 
     
    
     DETAILED DESCRIPTION OF THE DRAWINGS  
       [0028]    Definitions  
         [0029]    As used in this specification, the following terms have the following associated meanings.  
         [0030]    “NMR procedure” refers to any procedure that relies on nuclear magnetic resonance. Examples include, but are not limited to, magnetic resonance imaging (“MRI”), magnetic resonance angiography (“MRA”), and magnetic resonance spectroscopy (“MRS”).  
         [0031]    “Radio-opaque” refers to a property of a material that enables it to block RF energy. A material described in this patent application as “radio-opaque” need not block all RF energy; it merely must block RF energy to an extent that those with skill in the art would recognize it as providing sufficient RF shielding to prevent unwanted RF signals from interfering with an NMR procedure. Radio-opacity depends on a number of factors, including the type of the material, as well as the thickness and density of the component that uses the material, as well as the sensitivity and functioning of the equipment used to conduct the NMR procedure. Examples of materials that are radio-opaque in the frequency ranges typically used for NMR procedures are metals such as copper, aluminum, stainless steel, beryllium, and titanium. A semi-transparent radio-opaque shield may be formed of a radio-opaque metal screen, such as a copper screen, encased in acrylic.  
         [0032]    “Non-ferromagnetic” refers to a material that is substantially comprised of materials other than ferromagnetic materials (materials which may be attracted to a magnet). Ferro-magnetic materials are generally not used in the NMR environment because they will be attracted to the NMR magnet.  
         [0033]    “Holder” refers to a member that supports, and (in some embodiments) surrounds, a patient support unit, and in embodiments of the invention may comprise a bottom portion, a canopy, a patient end cap, and a base, as described in more detail below with reference to FIGS. 1, 1A,  1 B and  1 C.  
         [0034]    “Magnet end” (of a holder) refers to the end of the holder that is adjoined to the magnet in an NMR procedure.  
         [0035]    “Patient end” (of a holder) refers to the opposite end of the holder from the “magnet end.” 
         [0036]    “Patient end” (of a magnet) refers to the end of the magnet cavity into which the patient is inserted.  
         [0037]    “Service end” (of a magnet) refers to the opposite end of the magnet cavity from the patient end.  
         [0038]    “Magnet-RF-shielding” refers to RF shielding associated with the NMR magnet, which may include RF shielding provided by the magnet cryostat and/or RF shielding provided by a radio-opaque service end cap placed over the service end of the magnet.  
         [0039]    “Holder-RF-shielding” refers to RF shielding associated with the holder of the invention, which may include shielding provided by the bottom portion of the holder, the canopy, and/or a patient end cap.  
         [0040]    “Animal” refers to nonhuman animals. While the embodiments of the invention described in this specification relate to providing NMR procedures for non-human animals, the present invention can also be used for providing NMR procedures to humans.  
       DETAILED DESCRIPTION  
       [0041]    An exemplary embodiment of the present invention will now be described. Referring to FIGS. 1, 1A and  1 B, a system for use in an NMR procedure comprises a holder  103  (comprising bottom portion  105  and canopy  109 ) and a magnet  115  and associated components (including cryostat  117  and service end cap  119 ). Bottom portion  105 , canopy  109 , cryostat  117  and service end cap  119  are all radio-opaque. When the holder  103  is adjoined to the magnet  115  and service end cap  119  is put in place at the service end  118  of magnet  115 , a substantially complete RF shield is formed, consisting of canopy  109 , bottom portion  105 , cryostat  117 , and service end cap  119 . The term “adjoined to,” as used in this specification, refers to the position of holder  103  in relation to magnet  115  such that an RF shield is formed from holder-RF-shielding and magnet-RF-shielding.  
         [0042]    In the embodiment depicted in FIGS. 1 and 1B, bottom portion  105  contains or is made of a non-ferromagnetic radio-opaque material. As depicted in FIG. 1B, bottom portion  105  includes longitudinal track  112  for engaging a patient support unit, as depicted in FIGS. 2A and 2B. As shown in FIG. 1B, when bottom portion  105  is adjoined to magnet  115 , track  112  of bottom portion  105  aligns with track  121  of magnet  115 , to facilitate smooth transfer of the patient support unit from bottom portion  105  to magnet cavity  116 . Bottom portion  105  may be attached to or integral with base  107 , which may be mounted on wheels or casters for moving holder  103  to and from magnet  115 .  
         [0043]    In an embodiment, canopy  109  (depicted in FIGS. 1, 1B and  1 C) is constructed of or contains a radio-opaque material such as copper or aluminum. In an embodiment, canopy  109  is semi-transparent to facilitate observing the patient during preparation and during an NMR procedure. A suitable, radio-opaque semi-transparent canopy  109  can be fabricated by encasing a radio-opaque metallic screen, such as a copper screen, in acrylic. Canopy  109  can be a separate component of the holder  103 , which can be placed on top of bottom portion  105  to form a cylindrical shield. In an embodiment, canopy  109  can be placed on bottom portion  105  without locking canopy  109  into position. In some embodiments, the edges of canopy  109  comprise electrically conductive screen or other electrically conductive connections so that a pressure applied to the bottom surface of the canopy  109  and the corresponding top surface of bottom portion  105  will produce an electrical contact, thereby completing an RF shield composed of bottom portion  105  and canopy  109 . In some embodiments, clamps (not depicted) attached to bottom portion  105  swing upward to engage canopy  109 , thereby providing the pressure useful in maintaining electrical contact.  
         [0044]    In alternative embodiments (not depicted), the canopy can be hinged to either the magnet or the bottom portion of the holder. In one example of such an embodiment, the canopy comprises two halves, hinged to opposite sides of the bottom portion of the holder, such that swinging the halves upward results in formation of the canopy. In such embodiments, the holder may have a base in the shape of an inverted T, similar to that of base  107  depicted in FIGS. 1B and 1C, to accommodate the canopy halves when the canopy is not in use. In embodiments where the canopy is hinged to either the magnet or the holder, the hinges and associated components can also provide electrical contact useful in completing the RF shield.  
         [0045]    In the embodiments depicted in FIGS. 1, 1B, and  1 C, canopy  109  is shaped so that when canopy  109  and bottom portion  105  are attached, they form a cylinder that is closed at the patient end and open at the magnet end. The shape of the canopy is not critical to the invention; it merely must provide room for patient support unit (such as patient support unit  131  depicted in FIG. 1C), including the patient and any RF coils.  
         [0046]    In other embodiments (not depicted), the RF shield formed by a canopy and a bottom portion is a cylinder that is open at both ends. In such embodiments, the patient end of the cylinder may be covered with a patient end cap to complete the RF shield. Such a patient end cap may be made of radio-opaque metal, or of a radio-opaque metallic screen, such as a copper screen, encased in acrylic, or other radio-opaque materials. In such embodiments, the RF and physiological connections to the patient end cap may be routed through apertures in the patient end cap. The patient end cap can be attached to the canopy or the bottom portion, or both, by means of hooks, clasps, clamps, clips, screws, bolts, hinges, and other similar means.  
         [0047]    The holder  103  of this invention can be designed to operate with existing NMR magnets, or the holder  103  and magnet  115  can be designed and built as a system. In the embodiment depicted in FIG. 1, magnet  115  is cylindrical in shape, and has a cylindrical magnet cavity  116  extending through the length of magnet  115 . Magnet  115  may be a superconducting magnet, an electromagnet, or a permanent magnet.  
         [0048]    In the case of a superconducting magnet, as depicted in FIG. 1B, the magnet  115  may have a cylindrical cryostat  117  formed on its inner diameter. Cryostat  117  typically holds a cryogen, such as liquid helium, in which the superconducting magnet wire is contained. In embodiments of the present invention, cryostat  117  is made of radio-opaque material and provides sufficient RF shielding to be used as a portion of the RF shield of the present invention. Because cryostats made of radio-opaque stainless steel are features of many existing NMR magnets, it may not be necessary to modify such magnets in order for them to operate with the holder of the present invention.  
         [0049]    A holder  103  according to the present invention can also be used with an NMR magnet  115  that has a cryostat  117  that is not made of radio-opaque material, or an NMR magnet, such as a permanent magnet, that does not have a cryostat. In the case of a magnet that does not have a cryostat, a radio-opaque sleeve (not depicted), constructed, for example, of a radio-opaque screen stretched over a cage structure or cylinder (such as a tube) formed from non-ferromagnetic materials, can be inserted into the cavity  116  of the magnet  115  to provide a radio-opaque shield. In an embodiment, the radio-opaque sleeve is open at its service end, and the sleeve combines with service end cap  119  to complete the RF shield within the magnet  115 . In another embodiment, the radio-opaque sleeve has a closed end, and use of service end cap  119  is optional.  
         [0050]    In an alternative embodiment that can be used where the NMR magnet  115  does not have a cryostat  117 , an RF shield, for example a copper screen, can be provided on the outside of the magnet  115 . In such an alternative embodiment, the RF shield should be configured so that it surrounds magnet  15  (except for the opening of magnet cavity  16 ). In such an embodiment, the screen could be connected, and electrical contact provided, to holder  103  at the patient end of magnet  115 .  
         [0051]    In some embodiments, the RF shield for the NMR procedure can be formed without RF shielding provided by the holder. For example, in some cases, the NMR magnet is of sufficient length to permit placement of the patient into the magnet without the patient or patient support unit extending out of the opening of the magnet. In such cases, a radio-opaque RF screen similar to the service end cap  119 , with penetrations for electrical lines for RF coils and monitoring devices, can be placed over the opening at the patient end of the magnet to complete the RF shield for the NMR procedure. Such a radio-opaque screen may be attached or attachable to the patient support unit as well as to the magnet. In other embodiments, the radio-opaque bore may be extended to a length sufficient to achieve the same purpose, for example by use of a radio-opaque cylinder of the same diameter as the bore of the magnet, which may be integral with or attachable to the magnet. In such an embodiment, the RF shield may be completed by covering the patient end of the radio-opaque cylinder with a radio-opaque RF screen similar to the service end cap  119 . In some embodiments, the radio-opaque cylinder can support any portion of the patient support unit that extends out of the opening of the magnet. In other embodiments, a radio-opaque cylinder may be attached to or an integral part of the patient support unit. In such embodiments, the radio-opaque cylinder may have a radio-opaque base at the patient end, such that when the radio-opaque cylinder is connected to the magnet, a substantially complete RF shield comprising RF shielding provided by the radio-opaque cylinder, and magnet-RF-shielding, is formed. In some embodiments that do not rely on the holder to provide RF-shielding, the magnet has associated with it, for example as an integral part or as a removable attachment, a ledge for supporting any part of the patient support unit that extends out of the magnet.  
         [0052]    In the embodiment depicted in FIG. 1A, magnet  115  has associated with it a service end cap  119  for providing RF shielding over the opening at the service end  118  of magnet  115 . Service end cap  119  may be made of non-ferromagnetic metal, such as stainless steel, aluminum, or copper, or metal screen such as copper screen, and may include apertures for gradient and imaging cables. Service end cap  119  can be attached to the service end  118  of magnet  115  by means of hooks, clasps, clamps, clips, screws, bolts, hinges, and other similar means.  
         [0053]    In the embodiment depicted in FIG. 1B, magnet  115  includes RF seals  125 , to provide an electrical connection between holder  103  and magnet  115  to ensure the formation of a continuous RF shield.  
         [0054]    In embodiments of the present invention, magnet  115  also has a docking mechanism (not depicted) for engaging with a docking mechanism (not depicted) on holder  103  to dock holder  103  to magnet  115 . The docking mechanisms align holder  103  with magnet cavity  116 , and track  112  with track  121  (depicted in FIG. 1B), and ensure proper placement of the holder  103  in relationship to the magnet cavity  116 , thus facilitating easy transfer of the patient support unit  131  into magnet cavity  116 .  
         [0055]    [0055]FIGS. 2 and 2A depict an embodiment of patient support unit  131 , comprising bed  132 , bottom section  136 , RF coil block  135 , lower RF coils  139  mounted on RF coil block  135 , and upper RF coil  137 . Bed  132  is made of or coated with a material that is suitable for holding an animal, for example, an easily cleanable, waterproof material that also provides comfort and stability to the animal. Various plastics and non-conductive materials, including but not limited to fiberglass, Teflon or polyvinyl chloride, are suitable for this application. In the embodiment depicted in FIG. 2A, bed  132  is an integral part of bottom section  136  of patient support unit  131 . In other embodiments, bed  132  simply rests on bottom section  136  of patient support unit  131 ; in still other embodiments, bed  132  removably attaches to bottom section  136  of patient support unit  131 .  
         [0056]    Bed  132  is shaped to accommodate an animal. In an embodiment, bed  132  is shaped to accommodate the curvature of the animal&#39;s spine, in order to facilitate holding the animal in an inverted position. Thus, bed  132  may have a V-shaped cross section, a U-shaped cross section, or any other cross section that may be suited to hold a particular animal. The V-shaped bed used in the embodiments depicted in FIGS. 2, 2A and  2 B accommodates the spine of many animals, such as many types of cats and dogs, such that the spine of the inverted animal is positioned substantially in or near the vertex of the “V”, and therefore in close proximity to lower RF coils  139 — which, as described below, may also have V-shaped cross-sections—for optimal imaging.  
         [0057]    In the embodiment depicted in FIG. 2, patient support unit  131  has associated with it upper RF coils  137  (of which only one is depicted) and lower RF coils  139 . In the embodiment depicted in FIGS. 2 and 2A, lower RF coils  139  are mounted on RF coil block  135 , which conforms to the shape of bed  132 . In the embodiment depicted in FIG. 2, RF coil block  135  is V-shaped to conform to V-shaped bed  132 . In an embodiment, RF coil block  135  is movable in a longitudinal direction, for example along a track (not depicted) formed on the bottom section  136  of the patient support unit  131 . Thus, for example, when the patient is placed on bed  132 , lower RF coils  139  can be moved forward or backward such that an image of the desired portion of the patient&#39;s spine or abdomen can be obtained. In one embodiment, RF coil block  135  can be moved by manipulation of manual controls on the outside of holder  103 , where the manual controls comprise a pulley and wheel system. In another embodiment, RF coil block  135  can be moved back and forth by means of a push-pull stick. The movable RF coil arrangement of embodiments of the invention provides one way for the NMR operator to obtain images of different parts of a patient&#39;s body, without moving the patient.  
         [0058]    In the embodiment depicted in FIG. 2, lower RF coils  139  may function as a plurality of separate coils, or some or all of them may be connected in series to operate as an array of coils. In some embodiments, lower RF coils  139  comprise parts mounted on each side of RF coil block  135 . For example, in some embodiments, lower RF coils  139  are non-planar coils with two loops, such as figure-eight-shaped coils, such that one loop of the coil is mounted on one side of RF coil block  135 , and the other loop of the coil is mounted on the opposite side of RF coil block  135 . Accordingly, in some embodiments, for a V-shaped bed  132  and V-shaped RF coil block  135 , the lower RF coils  139  have a V-shaped cross-section, and are thus well-positioned for imaging the spine of an animal in or near the vertex of the “V” of the V-shaped bed. In such a configuration, non-planar lower coils  139  may function as partial volume coils, because they partially surround the object being imaged. In some embodiments, lower RF coils  139  comprise parts mounted on only one side of RF coil block  135 .  
         [0059]    In embodiments of the present invention, each lower RF coil  139  can also be used in combination with a “mate,” such as upper RF coil  137 , placed above bed  132  to complete a volume coil. In this manner, as depicted in FIG. 2A, the forward lower RF coil  139  combines with upper RF coil  137  to form a volume coil for imaging the head of the patient. In the same manner, lower RF coils  139  can be combined with upper RF coils for forming volume coils for imaging a patient&#39;s abdomen, as another example. When used, upper RF coils  137  may be plugged into connections (not depicted) in patient support unit  131 , to connect them to the appropriate lower RF coils  139 . An upper RF coil  137  may comprise a single coil, or an array of coils. The ability to create new RF coils—such as volume coils—by combining lower RF coils  139  with upper RF coils  137  enables the NMR operator to obtain images of different parts of a patient&#39;s body, without moving the patient.  
         [0060]    Patient support unit  131  can thus accommodate a wide variety of different RF coil configurations and designs, as will be apparent upon practicing the invention.  
         [0061]    In the embodiment depicted in FIG. 2, patient bed  132  includes an aperture or apertures (not depicted) to allow for drainage of the patient&#39;s urine or other bodily fluids from the bed into fluid collection container  143 .  
         [0062]    In the embodiment depicted in FIGS. 2A and 2B, RF, physiological monitoring, and other internal electrical or other lines  138  run from the interior of patient support unit  131 , including from RF coils  137  and  139  and from bed  132 , to internal electrical panel  133 , which connects them to external electrical panel  123  on bottom portion  105  (depicted in FIGS. 1 and 1B). In the embodiment depicted in FIGS. 1 and 1B, external electrical panel  123  is connected, via external lines  134 , to magnet electrical panel  122  on magnet  115 . Other arrangements for providing connections to the patient support unit will be apparent upon practicing the invention.  
         [0063]    In embodiments of the invention, the patient support unit bottom section  136  is shaped substantially to conform to the bottom portion of magnet cavity  116 . In the embodiment depicted in FIGS. 1B, 2 and  2 A, patient support unit bottom section  136  forms groove  141 , which is shaped to receive track  112  of holder bottom portion  105  and track  121  of magnet  115 , to allow for sliding of the patient support unit along the tracks in holder bottom portion  105  and magnet  115 . In addition, in the embodiment depicted in FIG. 1B, in which magnet cavity  116  is cylindrical, patient support unit  131  is curved at least in part with a curvature that substantially matches that of cavity  116 .  
         [0064]    In embodiments of the invention, patient support unit bottom section  136  is constructed of a material that allows for optimal sliding within the magnet cavity  116 . Good slidability may be achieved when patient support unit bottom section  136  is made of or coated with Teflon-coated fiberglass, and the bore of the magnet cavity  116 , or cryostat  117 , is made of or coated with Teflon-coated carbon fiber. Appropriately coated materials for these purposes can be obtained from M.T.D. Inc., 24 Slabtown Creek Road, Blairstown, N.J. 07825.  
         [0065]    A patient support unit of this invention, such as patient support unit  131  of the embodiment depicted in FIGS. 2, 2A, and  2 B, can be used independently of the RF-shielded holder of the invention described above, as, for example, when RF shielding is provided by a faraday cage.  
         [0066]    An embodiment of the invention as depicted in FIGS. 1, 1A,  1 B,  1 C and  2 A can be used to conduct an NMR procedure as follows, although the steps need not be performed in the particular sequence, and alternate procedures will be apparent from use of the invention. A patient, typically anesthetized, is placed in an inverted position in bed  132 , which is already in patient support unit  131  (as shown in FIG. 2A), which in turn has been placed in holder bottom portion  105  (as shown in FIG. 1C). Optionally, the patient&#39;s limbs may be strapped down by means of straps (not depicted) to prevent movement. RF coils  137  and  139  are then positioned appropriately for the NMR procedure to be conducted and the part of the body to be imaged. If not already in place, holder  103  is moved to and docked to magnet  115 , in order to facilitate transfer of the patient support unit  131  to magnet  115 . If not already in place, service end cap  119  is placed on the service end  118  of magnet  115 , in order to complete the portion of the RF shield associated with magnet  115 . Patient support unit  131  is then moved, typically manually, from holder bottom portion  105  into cavity  116  of magnet  115 , by sliding it from track  112  to track  121 . Patient support unit  131  may be inserted partially or fully into the magnet  115 , depending on the procedure to be conducted. If patient support unit  131  is partially inserted, the patient end of patient support unit  131  remains partially on track  112  and is supported by holder bottom portion  105 . Canopy  109  is placed on top of holder bottom portion  105  to complete an RF shield around patient support unit  131  and the patient. The NMR procedure may then be performed.  
       CONCLUSION  
       [0067]    While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not limitation. For example, the present invention is not limited to the physical arrangements or dimensions illustrated or described; the holder need not be cylindrical in form; and, depending on holder design, a patient end cap may or may not be used. Nor is the present invention limited to any particular design or materials of construction. The breadth and scope of the present invention should not be limited to any of the above-described exemplary embodiments, but should be defined in accordance with the following claims and their equivalents.