Magnetic resonance imaging system, apparatus and associated methods

In one aspect, a magnet comprising a pair of pole supports spaced apart from one another and extending in a generally horizontal direction. The magnet includes a pair of flux return members extending between the pole supports so as to define a frame, each of the flux return members including a first columnar section that extends parallel to the polar axis and a second columnar section that extends perpendicular to the polar axis and projects towards the pole. In another aspect, a magnetic resonance imaging system comprises a ferromagnetic frame that is operative to support an upper pole member and a lower pole member along a vertical polar axis such that a gap is defined between the upper and lower pole members and an access floor that is isolated from the ferromagnetic frame and pole members for providing access to the gap.

BACKGROUND OF THE INVENTION

The present patent application relates to magnetic resonance imaging apparatus and methods for using such apparatus in surgical procedures.

In magnetic resonance imaging, an object to be imaged as, for example, a body of a human subject is exposed to a strong, substantially constant static magnetic field. The static magnetic field causes the spin vectors of certain atomic nuclei within the body to randomly rotate or “precess” around an axis parallel to the direction of the static magnetic field. Radio frequency excitation energy is applied to the body, and this energy causes the nuclei to “precess” in phase and in an excited state. As the precessing atomic nuclei relax, weak radio frequency signals are emitted; such radio frequency signals are referred to herein as magnetic resonance signals.

Different tissues produce different signal characteristics. Furthermore, relaxation times are a dominant factor in determining signal strength. In addition, tissues having a high density of certain nuclei will produce stronger signals than tissues with a low density of such nuclei. Relatively small gradients in the magnetic field are superimposed on the static magnetic field at various times during the process so that magnetic resonance signals from different portions of the patient's body differ in phase and/or frequency. If the process is repeated numerous times using different combinations of gradients, the signals from the various repetitions together provide enough information to form a map of signal characteristics versus location within the body. Such a map can be reconstructed by conventional techniques well known in the magnetic resonance imaging art, and can be displayed as a pictorial image of the tissues as known in the art.

The magnetic resonance imaging technique offers numerous advantages over other imaging techniques. MRI does not expose either the patient or medical personnel to X-rays and offers important safety advantages. Also, magnetic resonance imaging can obtain images of soft tissues and other features within the body which are not readily visualized using other imaging techniques. Accordingly, magnetic resonance imaging has been widely adopted in the medical and allied arts.

Many conventional magnetic resonance imaging instruments require that a patient lie on a horizontal bed that is then advanced into a tubular bore within a super-conducting solenoidal magnet used to generate the static magnetic field. These units force the patient to undergo an intensely claustrophobic experience while being imaged. Other forms of magnetic resonance imaging apparatus, commonly referred to as “open MRI apparatus,” were developed to provide a less claustrophobic experience to the patient and greater access to the patient by medical personnel during the imaging procedure. However, even in this improved apparatus, the patient was still positioned inside the apparatus, and medical personnel attending to the patient would reach into the apparatus from outside, so that components of the apparatus still obstructed access to some extent.

As described in U.S. Pat. Nos. 6,335,623 and 6,541,973, which are assigned to the assignee of the present application, the disclosures of which are hereby incorporated by reference herein, this problem can be solved completely by providing space within the apparatus itself to accommodate medical personnel in addition to the patient. Thus, as shown in certain embodiments disclosed in the '973 and '623 patents, the magnet may include a ferromagnetic frame incorporating a floor, a ceiling and a pair of side walls extending between the floor and the ceiling, a lower ferromagnetic pole structure projecting upwardly from the floor and an upper ferromagnetic pole structure projecting downwardly from the ceiling. The projecting pole structures define a patient-receiving space between them. The magnet also includes flux generating elements such as resistive or superconducting coils or permanent magnets arranged to direct flux through the frame so that the flux passes through the patient-receiving space between the pole structures and returns through the side walls, floor and ceiling. The space between the side walls may be of essentially any size, but is desirably sufficient so that medical personnel can enter into the space along with the patient. In effect, the frame forms a room with a pole structure projecting down from the ceiling and another pole structure projecting up from the floor. The medical personnel inside the room have essentially unobstructed access to the patient from any side. It is, thus, quite practical to perform surgery or other medical procedure on a patient while the patient is in the patient-receiving space of the MRI apparatus. The room defined by the magnet frame may be equipped with features normally found in operating rooms, so that the magnet effectively becomes an MRI-capable operating room. Thus, surgery or other procedures can be performed under MRI guidance.

As shown in detail in the '973 patent, a patient positioning device may include a chassis having a pair of vertically extending end portions or leg portions and a bridge portion extending between these leg portions. The end portions of the chassis are spaced apart by a distance greater than the dimension of the lower pole structure. A bed is movably mounted to the chassis so that the bed can move and pivot in various directions relative to the chassis. The chassis is provided with wheels so that the patient can be positioned in the patient-receiving space of the magnet by placing the patient on the bed and wheeling the chassis into position, with the end portions of chassis disposed on opposite sides of the lower pole structure and with the bridge portion of the chassis spanning across the lower pole structure, so that the bridge portion of the chassis and the bed lie within the patient-receiving space. The patient can then be repositioned in various ways as by turning the bed about a vertical axis, tilting the bed about a horizontal axis or sliding the bed relative to the chassis. These arrangements provide extraordinary versatility in imaging of the patient and in positioning the patient for medical procedures. However, still further improvement would be desirable. For example, the MRI magnet typically is equipped with a false floor covering the ferromagnetic floor. The wheels of the chassis rest on the false floor. Any vibration or movement of the false floor will result in corresponding movement of the patient relative to the magnet. Further, the frame of the magnet must be designed to accommodate the full range of positions and orientations without comprising the susceptibility of the magnet to other sources of vibrations. In addition, the patient positioning device must incorporate mechanical features such as bearings and slides to allow movement of the bed relative to the chassis. It is difficult to accommodate bearings and slides of sufficient strength to allow for all of the desired ranges of movement while still providing a firm, secure support.

The present invention addresses the foregoing needs.

SUMMARY

In one aspect, a magnetic resonance imaging magnet is provided. The magnet comprises a pair of pole supports spaced apart from one another and extending in a generally horizontal direction and a pair of poles, each pole projecting from a respective one of the pole supports along a polar axis that is substantially perpendicular to the horizontal direction so as to define a patient receiving space therebetween. The magnet may further desirably include a pair of flux return members extending between the pole supports so as to define a frame, each of the flux return members including a first columnar section that extends parallel to the polar axis and a second columnar section that extends perpendicular to the polar axis and projects towards the pole.

In accordance with this aspect of the present invention, the pole supports, poles and flux returns are preferably made from ferromagnetic materials. It may be further desirable that these structures be made from low silicon steel or low carbon steel. Most preferably, the poles are made using low silicon steel, whereas the frame is made using low carbon steel.

Further in accordance with this aspect of the present invention, the magnet may further comprise at least two coils, at least one of the coils encircling each of the poles and being operable to provide magnetic flux in the patient receiving space. Further still, the coils may comprise either a resistive electromagnetic coil or a superconducting coil. The superconducting coils may further preferably comprise high temperature MgB2coils. Further still, the magnetic flux may be generated by a permanent magnet.

Further still in accordance with this aspect of the present invention, the magnet may further desirably include a pair of trusses or support members, each support member supporting one of the flux return members and being mounted on a plurality of vibration isolators. The vibration isolators may comprise air bags, elastomers or hydraulics.

The frame of the magnet may also further be supported on a well structure that includes a pair of support columns that project parallel to the polar axis and defining a well floor between them, and wherein each of the trusses or support members are respectively mounted to the support columns such that the frame of the magnet is isolated from the well floor.

Further in accordance with this aspect of the present invention, the flux return members are positioned apart from each other along the horizontal direction so as to define a work space around the poles of the magnet. Most preferably, the work space is large enough to accommodate a patient with any part of the patient's anatomy located in a imaging volume defined within the patient receiving space

In another aspect, the present invention is a magnet for magnetic resonance imaging. The magnet preferably comprises a pair of pole supports spaced apart from one another and extending in a generally horizontal direction; a pair of poles, each pole projecting from a respective one of the pole supports along a polar axis that is substantially perpendicular to the horizontal direction so as to define a patient receiving space therebetween; a pair of flux return members extending between the pole supports so as to define a frame; and a shield member that extends parallel to the horizontal direction and the direction of the polar axis and positioned relative to the frame and poles such that the shield member defines an interior space and an exterior space and wherein a magnetic field strength in the exterior space is substantially less than a magnetic field strength in the interior space. Most preferably, the shield is constructed from a plurality of relatively thin ferromagnetic sheets.

In another aspect, the present invention comprises a magnetic resonance imaging system. The system preferably comprises a ferromagnetic frame that is operative to support an upper pole member and a lower pole member along a vertical polar axis such that a gap is defined between the upper and lower pole members. The frame is preferably mounted to a well that includes a pair of support columns that project parallel to the polar axis so as to define a well floor between them, the ferromagnetic frame being mounted on the support columns. Further in accordance with this aspect of the present invention, the system desirably includes an access floor for providing access to the gap located above the well floor, the access floor being isolated from the ferromagnetic frame and pole members.

Further in accordance with this aspect of the present invention, the ferromagnetic frame is preferably mounted to the well support columns by a pair of support members, each support member being supported on one or more air bags. In addition, the access floor preferably comprises a floor plate mounted to a floor frame, the floor frame being supported by the well floor.

Further in accordance with this aspect of the present invention, the access floor further desirably includes an opening that includes a platform that may be elevated or lowered in a direction parallel to the polar axis and relative to the access floor.

The system may also be desirably equipped with a sensor system for detecting the presence of an object or person on the platform.

In yet another aspect, the present invention comprises a patient positioning system. The system preferably comprises a ferromagnetic frame that is operative to support an upper pole and a lower pole along a vertical polar axis such that a gap is defined between the upper and lower poles; a support frame mounted to the lower pole, the support frame including a pair of support beams extending parallel to each other on opposite sides of the lower pole; and a bed having a frame and a slab, the bed being mounted to the support frame such that each of the support beams engage the frame of the bed.

Further in accordance with this aspect of the present invention, the support is preferably rotatable around the lower pole. In addition, the beams are desirably operable to move the bed over the surface of the pole. Further still, the bed slab is desirably operable to cantilever relative to the lower pole. Most preferably, the frame defines a workspace that can provide access to surgeon to perform MRI guided intervention.

DETAILED DESCRIPTION

Turning now toFIG. 1, there is shown a magnetic resonance imaging system100in accordance with an aspect of the present invention. The system100includes a magnet106and a patient support apparatus110. The magnet106includes a lower magnet pole structure112that projects upwardly from a floor116. As is discussed in greater detail below, the floor116is a false floor that is supported by a floor of a well and is isolated from the magnet. The magnet106also includes an upper magnet pole structure120that projects downwardly from a ceiling122. For clarity, the upper magnet pole structure120is shown schematically in broken lines projecting downwardly through a portion of the ceiling122. Other structures associated with the magnet are located, beneath floor116above the ceiling122, and behind the side walls depicted123, but are not shown for clarity. These structures are discussed below. In addition, a front wall (not shown) is also used to house the system in a room, which may serve as an operating theater. The lower and upper pole structures112,120are aligned with each other along a polar axis124that generally extends vertically in the y-direction. The upper and lower pole structures112,120are spaced apart so as to define a patient receiving space128therebetween. As shown inFIG. 1, a patient P may be positioned within the receiving space128using the patient support system110. Other personnel O may then access the patient P while in patient receiving space128.

As shown inFIG. 1, the lower pole structure112is surrounded by a shroud130that is equipped to receive a patient support system110that is also included with the system100. The shroud130is equipped with a rotatable frame136that included ledges140onto which the patient support apparatus110may be docked and mounted. When the patient support apparatus110is mounted to the frame136it may be rotated about the polar axis124. In addition, the patient support apparatus110includes a frame138onto which a slab140is slidably mounted such that slab140is allowed to cantilever relative to the magnet pole. As such, either end of patient support apparatus,110, may project diagonally outward from the magnet pole and be rotated. This allows any portion of the patient's anatomy to be located in the iso-center of the magnet, i.e., within the center of the imaging volume.

The system100further includes a pair of safety gates150that are located at the front154of the magnet. Each gate150is connected to a rail156, which is mounted to the floor116. A lift platform160forms part of an elevator system, which is located towards the front154of the magnet. The rails156are equipped with a light gate sensor system164that detects the presence or absence of an object, e.g., medical personnel or bed132, that may be supported by the platform160. The light gate system164works in conjunction with an elevator system to automatically raise the lift platform160under certain conditions. In particular, if the lift platform160is recessed beneath the floor116and the gates150are opened, the lift platform160is automatically raised to be level with the floor116, unless a person or object is in the path of the light gate sensors164.

As an overview, the system100operates as follows. A patient is preferably loaded onto the patient support apparatus110in a staging area. The patient is then transported through the front154and positioned on the platform160. While on the platform160, the patient support apparatus is positioned with its longitudinal axis168aligned with the y-axis. The patient support apparatus110may then be raised to a suitable height such that it clears the lower magnet pole112. The patient support apparatus110is then moved over the magnet pole112into the patient receiving space or gap128. Once properly positioned over the pole112, the apparatus110is then lowered to engage the rotatable frame136at ledges140. With the patient support apparatus110mounted onto the frame136, safety rails170and legs174are then removed from the patient support apparatus. The patient may then be rotated and translated as discussed above so that the portion of the patient's anatomy to be scanned is located in the magnet's isocenter.

In addition to performing scanning, the system100also provides a versatile and open enough environment that can also accommodate one or more medical personnel in addition to the patient. For example, the system may be used in performing a biopsy or other medical procedure. In particular, the space around the poles provides an unobstructed view of a patient supported on the bed132in the gap128. An attendant or medical personnel may have 360° access to the patient from all locations. In addition, the platform160may be adjusted so as to accommodate the height of a doctor standing on the platform, who may be performing medical procedures using the images provided by a scan to pinpoint the location of tumors, tissue, bones or organs. In that regard, the system may also include a display (not shown) that is attached to the upper magnet pole so that a surgeon could view images in real time. The magnet design therefore provides an environment that can function as an operating room.

Alternatively, the system may be used to scan patients on an ambulatory or outpatient basis. In that regard, the system allows two or more patient support apparatus to be located in a staging area and used to load patients. When located in the staging area, the legs and wheels of the patient support apparatus are attached to the frame apparatus. In this mode, the patient apparatus is not docket to the lower pole, but is instead used to support and transport the patient to the front of the room housing the magnet. The patients may then be sequentially routed through the magnet106thereby improving the throughput of the system100.

Turning now toFIGS. 2A and 2B, there is shown perspective and front views of a magnet200that can be used in the system ofFIG. 1in accordance with an aspect of the present invention. InFIGS. 2A and 2B, the shroud, walls and other members that are used to make the magnet structures invisible to a user or patient are removed to reveal the support and other structural details associated with the magnet. In particular, the magnet200comprises an upper pole support210that extends horizontally across a pair of vertical flux return members214,216. A lower pole support220is located opposite upper pole support210and extends across vertical flux return members214,216. The pole supports210,220and flux return members214,216are preferably constructed using a plurality of ferromagnetic plates that are stacked together. As shown, the vertical flux return members214,216are C or U-shaped and include a horizontal run at their respective ends. The ends of flux return numbers214,216preferably terminate approximately two feet away from the magnetic poles in the preferred embodiment. The C-shaped vertical flux return members allows the distance between their inner side walls, which defines the width H of the room housing the magnet, to be wide enough to allow the patient support to cantilever as discussed above, yet while minimizing the length L of the unsupported upper and lower pole supports210,220. In particular, the C-shaped members214,216can be moved closer together than a vertical columnar structure would allow. This reduces the length L, which reduces the vibration of the poles, e.g., up and down, due to supports210,220. More particularly, the distance L2is preferably selected to be of a length that avoids mechanical vibration without providing a path for flux to leak from the pole into the vertical flux return members without going through the upper or lower pole support, which also functions as a flux return path or member. Put another way, L2must be chosen to prevent leakage across the gap G. In a preferred embodiment, H is approximately 160 inches and the vertical dimension V of the pole supports is approximately 16 inches.

The upper and lower pole supports and vertical flux return members define a frame or yoke that provides a magnetic circuit path for flux that is transported across a patient receiving space218between the lower pole221and an upper pole222. The magnetic flux is developed by a coil224that is shown encircling only lower pole221inFIG. 2A. A coil similar to that shown on pole221would also encircle upper pole222when the magnet is fully assembled. The coil224may comprise stacked layers of conductor turns that define a resistive electromagnet. The conductor turns may be aluminum or copper insulated by fiberglass tape. A cooling system is associated with the coils and may comprise any cooling system known in the art.

The resistive electromagnetic coil may be replaced by a conventional or high temperature superconducting coils. Superconducting coils are typically enclosed in vessels referred to as cryostats filled with a coolant such as liquid helium for conventional low temperature superconductors such as NbTi or Nb3Sn or, preferably, liquid nitrogen for high temperature superconductors. The coolant maintains coils at temperature low enough to provide superconductivity. The required temperature depends upon the composition of the superconducting material. The superconducting coils in their cryostats surround the poles in approximately the same position as resistive coils224.FIG. 2Cillustrates a cross-sectional view of a high temperature coil assembly240that may be used with magnet200in accordance with an additional aspect of the present invention. The high temperature coils may comprise MgB2coils or other high temperature coils. The coil assembly240includes a superconducting winding242arranged between coil support244. The coil supports244are capped using end caps246. Cooling tubes248are shown encircling coil support244and may include a gas at15degrees Kelvin such as provided by a cryro-cooler. The windings, coil supports, cooling tubes and other support structures are preferably housed in a vacuum box250. In the embodiment shown inFIG. 2C, the coil winding242extends approximately 12 centimeters between the end caps246and is approximately 0.5 centimeters thick. The box250is approximately 17 centimeters between its edges (2501and2502). The box is approximately 6 centimeters in width.

In addition to the electromagnets and superconducting coil assembly described and shown, the flux generating means may comprise permanent magnet material, which is preferably concentrated beneath the poles.

Returning toFIGS. 2A and 2B, the upper pole222is shown without coils that would normally likewise encircle it so as to reveal additional details associated with the construction of the poles. In particular, and as seen with respect to upper pole222, in the preferred embodiment each pole is generally cylindrical in shape and formed by stacking a plurality of circular ferromagnetic plates together to form pole stems. Each pole stem is connected to its respective support member using a base plate230. The lower pole221is preferably 4 to 7 feet across in diameter. In the preferred embodiment, the lower pole is 52 inches in diameter. Where the pole is of a smaller diameter it may be elongated along its polar axis to obtain the field strength needed with additional ampere turns.

As seen inFIGS. 2A and 2B, the lower pole support220is positioned within a U-shaped well270. A pair of support members274is mounted via a plurality of air bags275atop vertical columns276that form part of the well270. The support members274may comprise trusses or gussets that function to support the frame as shown. The trusses274are each connected to the vertical flux return members214,216via arms2781,2782, respectively. The trusses and air bags provide protection against vibration that may be caused by the surrounding environment. In addition, although in the preferred embodiment, the support members are mounted over air bags, other types of vibration isolators may be used in place of air bags. For examples, elastomers or hydraulics may be used to provide vibration isolation. The magnet200may be further secured by sway linkages280that provide additional protection against vibration.

As best seen inFIGS. 2A and 2D, a land bridge284is supported above the floor272of the well270. The land bridge284comprises a floor plate285that is mounted to a support frame. As shown inFIG. 2D, the support frame comprises a plurality of vertical and horizontal support members286. The support members2867through28610are arranged to provide an opening288for a lift platform290. The support frame includes additional openings through which the lower magnet pole221and vertical flux return members214,216are inserted. This arrangement allows the land bridge284and floor plate285to float relative to the magnet200or vice versa. More particularly, the magnet frame (structures210,214,216and220) and poles221,222are supported by the trusses274, which are supported by the air bags275. The air bags275protect against horizontal and vertical vibrations. As the land bridge is not supported by the air bags275, vibrations that may be caused by a person walking across the land bridge are not coupled to magnet200. In this way, such vibrations do not affect the imaging process. This ultimately leads to a reduction to the number of times a patient needs to be scanned, which increases scanning throughput.

Turning now toFIGS. 3A and 3B, there is shown an arrangement of an elevator system300in accordance with an aspect of the present invention. The system300comprises a lift platform310, which is mounted to four support stands312. The support stands312are mounted to respective screw jack rods316. Each rod316is threaded into a jack320. The jacks320are connected to electric motor326via a pair of rods328. In operation, the motor326rotates rods326, which results in the support stands being lowered or raised depending on the rotation direction. As discussed above, the elevator allows the height of a surgeon to be adjusted relative to the height of patient support when the patient support is mounted to the lower magnet pole. Such height adjustments aid in allowing a surgeon to more comfortably perform a surgical procedure. The lift may also be used for patient loading. For example, the lift may be used to lower the patient support apparatus or bed to a height that is more suitable to loading a patient in a wheel chair. After the wheel-chaired patient is loaded onto the bed, the lift is then raised to be level with the floor and the bed is docked and mounted as described in further detail below.

In addition to the structures discussed above, the magnet assembly in some circumstances may require localized shielding. For example, where the room housing the magnet needs to be of a depth that accommodates rotation around the lower pole with the bed cantilevered such that either a patient's head or feet is positioned in the imaging volume, localized shielding may be required to prevent leakage towards, for example, the rear of the magnet (seeFIG. 1, back wall199). Although magnets made using ferromagnetic materials, as discussed for example in relation toFIGS. 1 and 2, tend to have localized fields, leakage may occur into the electronics and other equipment that is needed to operate the magnet and other accessory equipment. In the embodiment ofFIG. 1, such electronics and equipment may be conveniently placed adjacent the rear wall199outside the room.

FIG. 4Ashows a side view of a magnet400that includes a localized shield410. As shown, the shield410is located behind back wall416. As best seen in the exploded view ofFIG. 4B, the shield410comprises a vertical member420and a horizontal member424. The shield410also includes a corner sheet428and an angle iron430.

The shield410may be constructed using four foot wide transformer sheets. As best seen inFIG. 4B, support struts440spaced 2 feet apart are secured to the scanner wall. Studs442cut from threaded rods are welded to the support struts440with a spacing of approximately 18 inches between studs. Clearance holes are punched in the transformer sheets permitting sheets to be slid onto the studs442. Holes are also punched along the edges of the transformer sheets to clear studs which are 2 feet away from the centerline of the transformer sheets. The sheets are then slid over the studs in an overlapping pattern as follows: sheet1is centered over the studs along strut4402; sheet2is centered over the studs along strut4404; and sheet3is overlaid over sheets1and2by centering it over the studs along strut4403. The pattern is repeated to extend beyond the sides of the magnet (length L inFIG. 2B) as required and to a thickness that prevents magnet flux leakage into the space beyond the shield wall. In a preferred embodiment, the rear vertical shield wall may employ 40 layers of 25 thousands thick M19 sheets which are 10 feet long (vertical direction). The horizontal section of the floor had 4 foot wide sheets of M19 placed above the floor at right angles to the vertical shield wall. Coupling between the horizontal and vertical shields are enhanced with 2 feet wide transformer sheets bent at 90° at their longitudinal centerline, i.e., ±1 foot on each side of the bend.

While the shield wall described above can be built up as described above, it may be easier to place multiple sheets over the studs at the same time at each location. When the outermost bundle edges butt up against each other, small straps secured to the studs assist in ensuring contact between the layers. The shielding described above has been shown to reduce flux leakage to earth field levels of about 0.5 Gauss immediately outside the magnet enclosure. This allows power supplies and other equipment behind the back wall to be shielded and obviates the need to warn operators and other staff that may be operating such equipment.

Turning now toFIG. 5A, there is shown a perspective view of a patient support apparatus110in accordance with an additional aspect of the present invention. The patient support apparatus or bed110may be considered as having three modes of operation or configuration: (1) gurney mode; (2) docking mode; and (3) pole mounted. Each of these modes will be described in detail below.

The bed110comprises a frame502which is supported by four detachable legs504. Each leg504includes a caster506that allows the bed110to be used to transport a patient from a staging area for imaging or a medical procedure, which we conveniently refer to as the gurney mode. The bed110also includes a slab510that is mounted to the frame502within a track that allows the slab to cantilever relative to the frame. The bed132also includes safety rails512which are mounted into openings518provided along the longitudinal edges of the frame502. The rails512are designed to fold inward when pressure is applied from outside the bed, but provides full support for the patient from within the bed frame. Control handles522are mounted to each end of the frame and, as is discussed in further detail below, are used to dock and mount the bed to the rotatable frame.

In particular, after a patient is loaded onto the bed, the bed110is then moved next to lower magnet pole530as is shown inFIG. 5Band prepared to be docked to the magnet pole530. The bed rails512are preferably first removed from the frame502before the bed is mounted, but may also be removed after the bed110is mounted to the rotatable frame. Next, the bed frame is raised to its docking position by lowering the handles522. As best seen inFIGS. 5C and 5D, the handle522is equipped with a pair of levers5221,5222that unlocks the handle522allowing it to be lowered, thereby causing the frame502and slab510to be raised. When the handle reaches the docking position it preferably locks into place to prevent any further unwanted lowering or raising of the bed110.

As best seen inFIG. 5EandFIG. 1, the bed110is then moved over the pole530, so that frame502is positioned over the rotation frame538mounted on the magnet shroud540at ledges542, which extend parallel to each other on opposite sides of the pole. A mounting beam544is secured at each ledge542. The beam544includes an inner base member544that is affixed to the mounting ledge542. A middle member544is slidably mounted into an opening546on the base member544. The opening546provides a track on which the middle member slides relative to the base member544. An outer member544is likewise slidably mounted on the middle member. Once the bed docks onto the rotation frame538, the bed132is slid towards the center of the magnet over the beam544. With the bed132centered on the magnet pole530, the handles522are then raised to their upright position causing the bed frame502to be lowered onto the beam544and rotation frame538. In this position, the entire weight of the bed is then supported by the rotation frame538.

With the bed110mounted to the frame502, the legs504may then be preferably removed. In the preferred embodiment, the legs are removed by grasping bar507and rotating it upward 90° and away from the magnet pole. A lever509is then used to release the legs from the frame.FIG. 6shows the bed132after it is mounted to the pole530and the legs have been removed. The legs504may include sensors that detect the presence of a load on the legs and prevent the legs from being removed from the bed frame.

As illustrated inFIG. 6, once the bed is mounted onto the pole530, or more particularly to rotation frame538at ledge542, it may then be rotated around the pole as is depicted by arrows A. As an additional safety feature, the rotation frame538is equipped with one or more stops570that allow the bed132to be docked at 0° of rotation as shown inFIG. 6, or 90° of rotation (line572) on the stop570shown. Note, however, that the bed110may rotate 360° about the polar axis. In addition to rotation about the pole530, the bed110may slide side-to-side along direction576. The slab of the bed may also cantilever on the beam544along the direction578. As discussed above, the members that comprise the beams are slidably relatively to each other along the ledge542. This additional adjustment allows for greater flexibility with respect to bringing a patient close to a doctor, who is standing at the edge of the pole.

Turning now toFIG. 7, there is shown a lighting configuration700in accordance with an additional aspect of the present invention. The lighting configuration700is desirably mounted to the upper magnet pole, e.g., pole124inFIG. 1, and is used to light the magnet gap128. As shown, the lighting configuration700includes a fixture704that is mounted onto a canopy pod708. The fixture704includes lamps710that provide ambient lighting. The lamps preferably comprise LED lights, which can be tilted within their fixture704from straight down to close to the center of the magnet. The fixture also includes a receptacle for a “goose neck” directional lamp716. The lamp716may be tilted towards the center of the magnet and provide lighting that is particularly focused on a portion of a patient's anatomy during a surgical procedure. In addition, in the preferred embodiment, the lamp is detachably mounted to the fixture704.

Turning now toFIG. 8, there is shown an alternate system800in accordance with an additional aspect of the present invention. In contrast to the system discussed in relation toFIGS. 1 through 7, the system800features a different bed assembly and magnet structure but may also be equipped with the magnet previously described. As seen inFIG. 8, a magnet810as taught in the aforementioned patents, includes a ferromagnetic floor812, a ferromagnetic ceiling (not shown) and a pair of ferromagnetic walls814and816. Although walls814and816are shown schematically inFIG. 8as planes, in fact, these walls have substantial thickness to provide adequate area for flux return. The magnet includes a lower pole structure818projecting upwardly from floor812and upper pole820structure, shown schematically in broken lines for clarity of illustration, projecting downwardly from the ceiling. The pole structures818and820are aligned with one another along a generally vertical pole axis822and define a patient-receiving space or gap824between them. The magnet incorporates a source of magnetic flux, such as one or more coils encircling one or both of the pole structures or other portions of the frame, which coils may be resistive or superconducting; or permanent magnet materials incorporated in the frame. The magnet provides a static field for magnetic resonance imaging. The MRI apparatus also includes conventional structures (not shown) such as a gradient coils for imposing magnetic field gradients within the patient-receiving space824; RF transmitting and receiving apparatus for transmitting radio frequency signals into the patient-receiving space and receiving the resulting RF signals emitted by the patient's body, commonly referred to as magnetic resonance signals. As is conventional in the MRI art, the magnet also incorporates a computer (not shown) and appropriate interfacing devices, so that the computer can control operation of the gradient coils and RF coils and reconstruct a magnetic resonance image from the received magnetic resonance signals. A display826may be mounted within the room enclosed by the frame for displaying the images. As described in the aforementioned patents, a structure of this type defines a working space indicated schematically at830inside the frame sufficient to accommodate one or more medical personnel inside the frame, along with the patient.

In the apparatus according to one embodiment of the invention, a lower pole shroud832surrounds the lower pole structure818of the magnet. The lower pole shroud832is mounted to the magnet frame as, for example, to lower pole structure818or to a portion of the ferromagnetic floor812surrounding the lower pole structure, so that the lower pole shroud can be rotated around polar axis822. For example, the lower pole shroud832can be supported by a large ball or roller bearing surrounding the lower pole structure818. The lower pole shroud is equipped with a pair of slide supports834and836extending generally parallel to one another on opposite sides of polar axis822. Each slide support is slidably mounted to the lower pole shroud832so that the slide support can be displaced in a slide direction indicated by arrow S inFIG. 8. A pair of retractable platforms838and840are provided on opposite sides of lower pole structure818. In the extended position depicted inFIG. 8, platforms838and840project outwardly, away from the pole structure. With lower pole shroud818in the position shown inFIG. 8, platforms838and840extend generally parallel to the slide direction S. The magnet is equipped with a false floor842overlying the ferromagnetic floor812. A portion844of the false floor is mounted on an elevating mechanism (not shown) so that the false floor can be moved between the flush position seen inFIG. 8, in which the portion844is flush with the remainder of floor842, and the elevated position844′ shown inFIG. 9, in which the portion844is raised slightly above the rest of the false floor842.

A patient support850includes a chassis having a generally horizontal bridge portion852and a pair of end portions or leg portions854and856extending downwardly from the bridge portion. Each end portion is equipped with wheels858. An elongated patient-supporting bed860overlies bridge portion852of the chassis. As best seen inFIG. 16, bridge portion852, bed860or both are equipped with anti-friction bearings or other elements which allow bed860to slide in a lengthwise direction L relative to the bridge portion852of the chassis. As best seen inFIG. 10, the bridge portion is equipped with slots864on its underside adjacent end portions854and856. These slots864are arranged to engage slides834and836.

The magnet is further equipped with an auxiliary support element870. This support element is mounted to a carrier872which, in turn, is supported on a rail874extending along one wall814of the magnet. In the retracted position seen inFIG. 8, auxiliary support870lies along wall14, and hence, does not occupy appreciable space within the magnet. As best seen inFIGS. 13,14and15, the auxiliary support870and carrier872can be moved along rail874to a position near pole axis822and lower pole shroud832, and the auxiliary support can be tilted downwardly into a substantially horizontal position (FIG. 15) in which the end of the auxiliary support remote from carrier872rests on the chassis of support850in alignment with bridge portion852. The auxiliary support870is equipped with anti-friction bearings876or other devices similar to those provided on the bridge portion852of the chassis.

In operation, a patient is loaded onto bed860, and the patient support chassis850is wheeled across false floor842onto platform portion844and platforms838and840are placed in their extended position. As seen inFIG. 9, platform portion844is raised to its elevated position844′ so that the platform portion is flush with platforms838and840. The patient support850is wheeled from the platform portion44onto the platforms838and840and engages slides834and836(FIGS. 9 and 10). The platforms838and840are retracted (FIG. 11), leaving the patient support850resting on slides834and836. In this condition, the center of bed60is substantially centered with the polar axis822. The patient can be imaged in this position. Moreover, medical personnel in working space850can perform surgical or other procedures on the patient.

As seen inFIG. 12, slides834and836can be extended to move the patient support850and bed860in slide direction S, so that the patient lies entirely outside of the patient-receiving space and does not lie beneath upper pole structure820. This position provides maximum exposure of the patient for surgical or other procedures. As seen inFIGS. 18 and 19, the lower pole shroud832can be rotated around polar axis22between the position illustrated inFIG. 19(the same position as shown inFIG. 8) and the position shown inFIG. 18, thereby rotating the patient support850and the bed860around the polar axis. This provides for repositioning the patient to a more convenient rotational position for surgery or other medical procedures.

As best appreciated with reference toFIGS. 14-16in sequence, auxiliary support870can be positioned in its fully extended position, where it interlocks with support850(FIG. 15), and the bed860can be moved in lengthwise direction L so that a portion of bed860rests on the auxiliary support870and another portion of bed860is supported by the bridge portion852of the patient support chassis. This allows for substantial movement in direction L so that extreme portions of the patient's anatomy, as for example, the feet or the head, can be aligned with polar axis822. Because a portion of the bed60is supported by the auxiliary support870, the anti-friction bearings or other elements incorporated in the bed and in a patient support50need not provide all of the structural support. Stated another way, in the position illustrated inFIG. 16, bed860projects beyond chassis850, but is not cantilevered. Instead, the projecting portion of the bed is supported on auxiliary support870. As best seen inFIG. 17, when the bed60is supported in part on the auxiliary support870, the auxiliary support870and carrier872can move along rail874, along with the movement of chassis850and slides834and836in the slide direction S. Thus, even where the patient is in an extreme position, the patient can move out of the patient-receiving space for access.

Although only one auxiliary support870is depicted in the present drawings, the magnet may include two or more auxiliary supports disposed on two or more walls, so that the auxiliary supporting action can be provided in different rotational positions of the lower pole shroud832. Also, the bed860can be moved slightly in directions L relative to chassis850without using the auxiliary support870, as for example, where the lower pole shroud832is an intermediate rotational position. Because patient support850is supported on the lower pole shroud832during imaging and lower pole shroud832, in turn, is supported on the ferromagnetic structure itself, vibrations or movement of false floor840will not affect imaging. Likewise, auxiliary support870is supported by a wall which is part of the ferromagnetic frame, and which is mechanically isolated from the false floor.

The components of the lower pole shroud832, patient support850, bed860and auxiliary support870desirably are formed from non-magnetic materials such as polymeric materials so that they do not interfere with the magnetic fields generated during use.

As mentioned above, the frames and poles of the magnets are preferably made with ferromagnetic materials. To achieve the field strengths at which the magnet is desired to operate, e.g., 6 Kilo-Gauss, it is further preferably to use low silicon steel that exhibits sufficiently high magnetic permeability in the polar regions. Low carbon steel is suitable and may be used in the frames. As magnet field strength increases pole saturation may place practical limits on the magnet design and place practical constraints on the size of the magnet poles, magnetic field strength and gap distance. The applicants have fabricated 3000 gauss magnets using grade 1008 steel. The applicants have found that grade 1006 steel is usable up to around 20,000 gauss and grade 1001 steel is usable up to around 22,000 gauss.

Numerous further variations and combinations of the features discussed above can be utilized without departing from the present invention. For example, the patient supports may be used with different magnets; the magnet need not include upper and lower projecting pole structures as shown. Also, with respect to the embodiments shown and discussed with respect toFIGS. 8 through 20, the end portions854and856of the patient support chassis may be arranged to extend and retract, and thereby raise and lower bridge portion852and bed860. In such a variant, the platform portion844of the false floor may be stationary, and the platforms838and840, discussed above, may be omitted. The patient support50may be positioned on slides834and836by rolling the patient support across the false floor, whereupon the end portions854and856of the chassis may be retracted so as to leave the chassis supported on the slides. Also, auxiliary support870may be replaced or supplemented by an arm, cable or strut extending from the ceiling element of the ferromagnetic frame.