Abstract:
A device for controlled orientation of a person&#39;s cervical spine that is compatible with medical imaging machines. The device is capable of rotation about the axis of a patient&#39;s spinal column independent of, or in addition to, flexion/extension of a patient&#39;s spinal column. The device may incorporate locking mechanisms to secure rotational orientation and may include quantitative indicators of the degree of rotation.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates generally to a medical-imaging compliant apparatus for adjusting a patient&#39;s head position to facilitate controlled orientation of the cervical spine during medical imaging.  
         [0002]     Medical imaging has become an indispensable tool for the diagnosis and treatment of conditions affecting a person&#39;s cervical spine. Images of the cervical spine provide doctors with insight into such conditions as cerebral spinal fluid flow patterns, nerve compression, spinal instability and intervertebral disk damage. Diagnosis of these, and other conditions, often requires that images of the patient&#39;s spine be taken while the spine is rotated about its axis or while undergoing flexion/extension. These specific configurations may need to be accurately recreated during subsequent imaging to facilitate diagnosis and treatment.  
         [0003]     Medical imaging technologies, such as those used in magnetic resonance (“MR”) imaging and computed tomography (“CT”) imaging, are extremely sensitive to the amount and type of material, as well as its location in relation to the area to be imaged, of any equipment present during imaging. MR imaging uses a strong magnetic field to polarize nuclei whose position is then detected by special coils. The presence of conductive or magnetic material disrupts the detection and thus spatial encoding of the signals—ultimately degrading the clarity of the image and the information the doctor is able to learn from the MR scan.  
         [0004]     CT imaging uses X-ray attenuation to reconstruct a three-dimensional image. Given that different materials and tissues cause varying attenuation of the X-rays used in a CT, it is critical that any support structure introduced into the scan be radiolucent, meaning the material does not substantially scatter or block the X-rays causing artifacts in the images.  
         [0005]     Conventional wisdom has lead inventors to design cervical rotation devices that remove supporting structure from the area to be imaged to reduce image artifacts. When the material is unable to be removed from the imaging area, plastics are commonly used because of their low interaction with both MR and CT imaging machines. The removal of structure from the imaging area along with the use of imaging compliant materials is advantageous as it reduces the amount of interference caused by the fixture, therefore providing a more informative image.  
         [0006]     One previous design consists of a head cradle shaped as a half-cylinder with one open end and one closed end. A pin mounted to the closed end supports the head cradle. The other end of the pin is rotatably mounted to the back of a frame having support legs extending on the left, back, and right of the head cradle minimizing the portion of the support structure within the imaging area of the head cradle. The design is effective at removing the majority of the structure from the imaging area; however, a single pin supports the entire weight of the patient&#39;s head. This cantilevered design places a tremendous amount of stress on the pin making it less suited for construction from CT and MR imaging compliant materials such as plastic. Additionally, orientating a patient&#39;s head is difficult given the high load placed upon the pin at the axis of rotation.  
         [0007]     Another design incorporates an outer ring with radial slots around a portion of the circumference. A head cradle shaped as an open-ended half-cylinder has two collinear pegs extending radially outward from the head cradle. The head cradle is suspended within the large outer ring by placing the two pegs through the radial slots in the outer ring and independently clamping each peg in place. This design eliminates the high stresses placed on the single pin in the previous design, but the head cradle may be difficult to rotate because the weight of the patient&#39;s head acts to wedge the pegs downward in the radial slots.  
         [0008]     It is critical that the portion of the spine being imaged remains immobile in the desired orientation throughout imaging. Common techniques to reduce head movement during imaging involve combinations of strategically located straps, clamps, and blocks. These techniques are time consuming and cumbersome because a health care professional must configure the individual pads and straps. The sight of clamps and straps may add to patient anxiety.  
       BRIEF SUMMARY OF THE INVENTION  
       [0009]     The present inventors have determined that placing a bearing surface substantially beneath the patient&#39;s head allows a sturdy and relatively rigid support to be constructed of lightweight, non-metallic materials that do not substantially interfere with the CT or MRI imaging process. Furthermore, the present inventors have recognized that a head support pad having a sufficient configuration and compliance can comfortably and unobtrusively maintain a patient&#39;s head position during rotation of the fixture during imaging.  
         [0010]     Specifically, the invention provides a fixture for adjusting a patient&#39;s head position in a medical imaging machine having a base supporting a head cradle defining a volume receiving and supporting a patient&#39;s head. The fixture also has a bearing, having first and second bearing surfaces moving with respect to each other about a first axis aligned with the patient&#39;s neck, the bearing is located between the base and the head cradle along a vertical line passing substantially through a center of mass of the patient&#39;s head when the head is at a predetermined position in the head cradle. The bearing is constructed of a material that is substantially transparent to the imaging machine.  
         [0011]     It is thus one object of at least one embodiment of the invention to provide a support for rotation of a patient&#39;s cervical spine that is both sturdy and compliant with medical imaging technologies. The bearing surface beneath the head allows use of radiolucent and nonferrous material to provide sturdy support and smooth rotation.  
         [0012]     The base may include a cradle support mounted to rotate about a second axis perpendicular to the first axis.  
         [0013]     Thus, it is another object of at least one embodiment of the invention to adjust the flexion and extension of a patient&#39;s cervical spine before axial rotation.  
         [0014]     The fixture may further include a first handle communicating with the head cradle to selectively rotate the head cradle about the first axis.  
         [0015]     It is thus another object of at least one embodiment of the invention to provide a convenient means of rotating the patient&#39;s head.  
         [0016]     The first handle may also selectively rotate the cradle support about the second axis.  
         [0017]     Thus, it is another object of at least one embodiment of the invention to provide a single means of controlling the rotation and flexion/extension of a patient&#39;s cervical spine.  
         [0018]     The first handle may include a first lock actuated by the first handle that selectively prevents rotation of the head cradle about the first axis.  
         [0019]     It is thus another object of at least one embodiment of the invention to provide a single control that facilitates rotation about the axis of a patient&#39;s cervical spine and locks the fixture in the desired position.  
         [0020]     The first lock may be a threaded member that is rotated to clamp the cradle support and the head cradle.  
         [0021]     Thus, it is another object of at least one embodiment of the invention to provide a simple and reliable lock mechanism that provides both mechanical advantage and allows for secure positioning about the axis of a patient&#39;s cervical spine over a range of orientations.  
         [0022]     The fixture may further include a second lock that selectively prevents rotation of the cradle support about the second axis.  
         [0023]     It is thus another object of at least one embodiment of the invention to separate the rotational locks to allow rotation about one axis independent of rotation about the other axis.  
         [0024]     The second lock may be a threaded member that is rotated to clamp the base to the cradle support.  
         [0025]     Thus, it is another object of at least one embodiment of the invention to provide a lock mechanism that provides a mechanical advantage and allows for secure flexion/extension positioning of a patient&#39;s cervical spine in an infinite number of orientations.  
         [0026]     The fixture may have a base configured to engage a medical imaging table.  
         [0027]     It is thus another object of at least one embodiment of the invention to provide a fixture that may be installed on a variety of machines.  
         [0028]     The fixture may include a first scale indicating rotation about the first axis from a predetermined position.  
         [0029]     Thus, it is another object of at least one embodiment of the invention to provide for quantitative measurement of the amount of rotation of the device about the axis of a patient&#39;s cervical spine.  
         [0030]     The fixture may include a second scale indicating rotation about the second axis from a predetermined position.  
         [0031]     It is thus another object of at least one embodiment of the invention to provide for quantitative measurement of the amount of flexion/extension of a patient&#39;s cervical spine.  
         [0032]     The fixture may further include a first marker mounted to the cradle support wherein the first marker is configured to be detected by a medical imaging device.  
         [0033]     Thus, it is another object of at least one embodiment of the invention to provide an indication of the position of the cradle support that will be preserved in the final image to aid in diagnostics.  
         [0034]     The fixture may further include a second marker mounted to the head cradle wherein the second marker is configured to be detected by a medical imaging device.  
         [0035]     It is thus another object of at least one embodiment of the invention to provide an indication of the position of the head cradle that will be preserved in the final image to aid in diagnostics.  
         [0036]     The bearing may also present a portion of a surface of a cylinder, the cylinder being coaxial about the first axis.  
         [0037]     Thus, it is another object of at least one embodiment of the invention to have a bearing surface that provides isocentric rotation and approximates the general shape of the back of a patient&#39;s head to decrease the height of the head cradle while providing a broad area of contact.  
         [0038]     The fixture may further include a mat sized and arranged to align the first axis and the axis of a patient&#39;s spine.  
         [0039]     It is another object of at least one embodiment of the invention to provide a simple method for aligning the axis of a patient&#39;s spine to allow for pure rotation of the patient&#39;s cervical spine while allowing the bearing to be placed below the head surface.  
         [0040]     The mat may be independent of the base.  
         [0041]     Thus, it is another object of at least one embodiment of the invention to have a mat that can be manipulated independently of the fixture to allow for interchangeability of the mat to accommodate different patients.  
         [0042]     Additionally, the invention provides a fixture for adjusting a patient&#39;s head position in a medical imaging machine having a base, a cradle support mounted to the base, and a head cradle communicating with the cradle support. The fixture also has a head support pad attached to the head cradle or the cradle support. The head support pad has a concave cross-section with a compliance that applies sufficient lateral pressure upon the temporal region of a patient&#39;s head, under the weight of an average patient&#39;s head, to substantially maintain the patient&#39;s head placement relative to the head cradle throughout movement of the head cradle and cradle support.  
         [0043]     It is thus another object of at least one embodiment of the invention to provide a convenient device to stabilize a patient&#39;s head position during medical imaging.  
         [0044]     Furthermore, the invention provides a fixture for adjusting a patient&#39;s head position in a medical imaging machine comprising a base, a first support and a second support attached to the base and extending upwardly from the base, an outer ring rotatably mounted between the first and the second supports having a first central axis and an inner surface sized to encompass a patient&#39;s head. Furthermore, the fixture has an inner ring having a second central axis and an outer surface sized to fit rotationally within the outer ring, wherein the first and second central axes are aligned.  
         [0045]     Thus, it is another object of at least one embodiment of the invention to provide a device easily manufactured from rotatably engaged concentric rings rotatably mounted between side supports.  
         [0046]     The fixture described above may further include a rollable bearing element and a first race sized to engage the bearing formed in the inner surface of the outer ring, the outer surface of the inner ring, or both.  
         [0047]     It is thus another object of at least one embodiment of the invention to have a device with smooth and continuous rotation to promote patient comfort and ease of use.  
         [0048]     The rollable bearing element may be a ball.  
         [0049]     Thus, it is another object of at least one embodiment of the invention to be readily manufactured from commonly available plastic ball elements.  
         [0050]     These particular objects and advantages may apply to only some embodiments falling within the claims and thus do not define the scope of the invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0051]      FIG. 1  is a perspective view of the present invention providing a fixture for rotating a patient&#39;s head axially in a medical imaging machine;  
         [0052]      FIG. 2  is a fragmentary section view along line  2 - 2  of  FIG. 1  showing a bearing for flexion/extension adjustment.  
         [0053]      FIG. 3  is a side view showing the fixture rotated to provide flexion of a patient&#39;s spine;  
         [0054]      FIG. 4  is a simplified end view of the embodiment of  FIG. 1  showing the fixture rotated axially;  
         [0055]      FIG. 5  is a fragmentary section view along line  5 - 5  of the embodiment of  FIG. 1 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0056]     With reference to  FIG. 1 , the cervical spine rotation fixture  9  constructed according to the present invention has a generally rectangular base  10  with a planar upper surface and a convex lower surface configured to engage a variety of medical imaging machine tables  11 , including a magnetic resonance (“MR”) imaging machine or a computed tomography (“CT”) imaging machine.  
         [0057]     A left pillar  12  and a right pillar  14  are attached in opposition at left and right sides of the base  10  and extend upwardly from the base  10  parallel to each other and perpendicular to the base  10 . As used herein, directions, such as “left” and “right”, will be with respect to a patient  86  lying supine on the patient table  11  with the patient&#39;s head above the base  10 .  
         [0058]     An outer ring  16 , having a central axis  18 , fits between the left and right pillars  12  and  14  to be supported thereby on a shafts  46  (shown also in  FIG. 5 ) passing through the left and right pillars  12  and  14  so that the outer ring  16  may rotate about a generally horizontal, flexion/extension axis  20  extending between the left and right pillars  12  and  14 . Ends of the shafts  46  are attached to plates  45  passing downward along the outer surfaces of the left and right pillars  12  and  14  to rotate with the shafts  46 .  
         [0059]     An inner ring  30  fits within the outer ring  16  to rotate therein such that the central axis  32  of the inner ring  30  is coaxial with the first central axis  18  of the outer ring  16 . The inner ring  30  thus rotates, with respect to the outer ring  16 , about the first and second central axes  18  and  32 .  
         [0060]     The outer ring  16  has a height measured along the central axis  18  of approximately one-half the height of an average human head measured in the superior/inferior direction and diameter slightly greater than the diameter of the average person&#39;s head. As shown also in  FIG. 3 , the inner ring  30  includes a lower shelf portion  33  extending in a superior direction approximately the height of the outer ring  16  beyond the outer ring  16 . The remainder of the inner ring is of the same height as the outer ring  16 .  
         [0061]     The outer ring  16  has a first slot  22  extending approximately  45  degrees circumferentially clockwise and counterclockwise from a vertical axis  24 . A handle  58 , to be described below, attaches to the inner ring  30  and extends through the slot  22 . As shown also in  FIG. 4 , first scale  26  is affixed to the outer ring  16  to show the degree of axial rotation (angle beta) of the inner ring  30  about the first central axis  18  as indicated by position of the handle  58 .  
         [0062]     The plates  45  likewise have arcuate slots  47  at a constant radius about axis  20  and of angular extent of approximately  30  degrees. Second handles  62  and  66 , also to be described below, attach to the left and right outer surfaces of the left and right pillars  12  and  14 , and extend through the slots  47 . As shown also in  FIG. 3 , second scales  28  are affixed to the plates  45  showing the degree of rotation (angle alpha) of the outer ring  16  and inner ring  30  in flexion/extension about axis  20  as revealed by the position of the handles  62  and  66  with respect to the scales  28 .  
         [0063]     Referring now to  FIG. 2 , the interface between the outer ring  16  and inner ring  30  provides a first and second race formed of opposed hemicylindrical grooves  34 ,  36  in each of the outer ring  16  and inner ring  30 , the grooves following a path coaxial with axes  18  and  32 . Each race has a hemicircular cross section approximately equal to the radius of a number of ball bearings  42  that may be placed in opposed grooves  34 ,  36  to provide a slight gap  44  between the inner ring  30  and the outer ring  16 .  
         [0064]     As shown in  FIG. 3 , the outer ring  16  may have fiducial markers  52  mounted in several locations around the circumference of the outer ring  16  to allow the location and flexion/extension orientation of the outer ring  16  to be captured by an imaging machine. The first markers  52  may have a circular cross-section and be constructed of radio opaque material for an x-ray CT or of an NMR contrast material, for example, a mixture of gadolinium and water, for MRI. Referring to  FIG. 4 , second fiducial markers  56  are mounted parallel to the second central axis  32  on the inner ring  30  to allow the axial orientation of the inner ring  30  to be captured by an imaging machine. The second markers  56  may also have a circular cross-section and be constructed of similar material to the first fiducial markers. The first markers  52  and second markers  56  are generally elongated such that the plane of a cross-sectional image will intersect a portion of the markers  52 ,  56 .  
         [0065]     Referring now to  FIG. 5 , relative rotation of the inner ring  30  about the central axes  18 ,  32  with respect to the outer ring  16  may be locked by rotating handle  58 . Handle  58  includes internal threads engaging a threaded stud  60  that extends radially outward from the inner ring  30  through the first slot  22  in the circumference of the outer ring  16 . Upon rotating the first handle  58 , the inner ring  30  and the outer ring  16  are clamped together.  
         [0066]     Likewise, rotation of the outer ring  16  and inner ring  30  about the flexion/extension axis  20  with respect to the left and right pillars  12  and  14  may be locked by turning the second handles  62  and  66 . Each of second handles  62  and  66  have internal threads receiving threaded studs  64  and  68 , respectively, extending horizontally outward from the left pillar  12  and right pillar  14  through an arcuate slots  47  in the respective plates  45 . Rotating these handles  62  and  62 , clamps the plates  45  to the respective pillar  12  or  14 .  
         [0067]     For use in MR imaging, all elements of the fixture can be made from non-ferromagnetic and non-conductive materials such as polycarbonate, acrylic, polypropylene, nylon, and polyvinyl chloride, for example. Additionally, when compliance with CT imaging is desired, the use of radiolucent materials with low mass attenuation coefficients is preferred (e.g., carbon composites).  
         [0068]     Returning briefly to  FIG. 1 , a rectangular mat  72 , sized and contoured to comfortably accommodate the body of an average person, has a central longitudinal axis  74  that is oriented parallel to the central axes  18 ,  32 . The mat  72  can be configured to be attached to the base  10  or separate from the base  10 . The mat  72  has an appropriate thickness  76  necessary to align the axis of a patient&#39;s spinal column  78  with the second central axis  32  of the inner ring  30 . In one embodiment, the mat  72  has a thickness  76  of approximately  4  inches. The mat  72  can be made from a variety of materials that provide sufficient comfort and support including, for example, foam, rubber, and plastic. Different mats  72  of different thicknesses can be used for different purposes and patients.  
         [0069]     As shown in  FIG. 1 , the head support pad  80  is sized to substantially encompass the posterior portion of a human head and is attached to the inner ring  30  approximately along the bottom half of the inner ring  30  and the shelf portion  33  of the inner ring  30  that extends beyond the outer ring  16 .  
         [0070]     Turning to  FIG. 4 , the head support pad  80  has a substantially concave cross-section and is constructed from a material with a compliance that deforms under the weight of an average patient&#39;s head  82 . The head support pad  80  supplies a counteracting force  84  around the temporal and posterior regions of the patient&#39;s head  82  that stabilizes the patient&#39;s head  82  and helps maintain the orientation of the patient&#39;s head  82  with respect to the inner ring  30  under rotation about the central axes  18 ,  32  and with respect to the outer ring  16  under rotation about the flexion/extension axis  20 . The head support pad  80  can be made from a material such as polyurethane foam or any other material having a sufficient compliance.  
         [0071]     Returning to  FIG. 1 , during use of the device, the patient is positioned in a supine position on the mat  72  with the patient&#39;s spinal column  78  coaxial with the central axis  18 ,  32  of the inner ring  30  and outer ring  16 . The patient&#39;s head  82  is placed within the inner ring  30  and secured by the head support pad  80 .  
         [0072]     Once the patient  86  is secured, a health care professional can easily adjust the patient&#39;s head  82  about the flexion/extension axis  20  with one hand on handle  58 . Referring again to  FIG. 5 , to lock the position about the flexion/extension axis  20 , the health care professional may use a second hand to tighten one of the second handle  62  and third handle  66 . The second scale  28  or third scale  70  provide the health care professional with an indication of the amount of rotation about the flexion/extension axis  20 .  
         [0073]     Once in the desired position, the health care professional may tighten the second handle  62  and/or third handle  66  to secure the outer ring  16  in place.  
         [0074]     To rotate about the patient&#39;s spinal column  78 , the health care professional may continue to move the first handle  58  while observing the first scale  26 . Once the desired axial rotation is reached, the health care professional may tighten the first handle  58  to secure the inner ring  30  in place.  FIG. 4  shows the device after rotation about the patient&#39;s spinal column  78 .  
         [0075]     It is specifically intended that the present invention not be limited to the embodiments and illustrations contained herein, but that modified forms of those embodiments including portions of the embodiments and combinations of elements of different embodiments also be included as coming within the scope of the following claims.