Patent Abstract:
A patient support structure for a laser imaging apparatus, comprises a tabletop to support a female patient in front-down, prone position. The tabletop includes an opening adapted to permit a breast of the patient to be vertically pendant below the tabletop. The opening is non-symmetric with respect to an axis of rotation of a scanning mechanism disposed below the tabletop.

Full Description:
FIELD OF THE INVENTION  
         [0001]    The invention relates generally to a diagnostic medical imaging apparatus that employs a near-infrared laser as a radiation source and particularly to a patient support structure having a tabletop with a breast positioning aperture to support a patient in a front-down prone position with her breast disposed vertically pendant in the aperture for scanning.  
         BACKGROUND OF THE INVENTION  
         [0002]    In recent times, the use of light and more specifically laser light to noninvasively peer inside the body to reveal the interior structure has been investigated. This technique is called optical imaging. Optical imaging and spectroscopy are key components of optical tomography. Rapid progress over the past decade has brought optical computed tomography to the brink of clinical usefulness.  
           [0003]    In optical tomography, the process of acquiring the data that will ultimately be used for image reconstruction is the first important step. Light photon propagation is not straight-line and techniques to produce cross-section images are mathematically intensive. To achieve adequate spatial resolution, multiple sensors are employed to measure photon flux density at small patches on the surface of the scanned object. The volume of an average female breast results in the requirement that data must be acquired from a large number of patches. The photon beam attenuation induced by breast tissue reduces the available photon flux to an extremely low level and requires sophisticated techniques to capture the low level signals.  
           [0004]    U.S. Pat. No. 5,692,511 discloses such a laser imaging apparatus, This apparatus supports a patient in a face-down, prone position on a horizontal surface with a breast vertically pendant through an opening in a table surface. The patient&#39;s breast is pendant within a scanning chamber surrounded by an array of detectors, which revolve around the centerline of the scanning chamber. The array of detectors forms a portion of a circle and the scanning chamber and the opening or aperture in the tabletop are therefore circular. Provision is made to accommodate breasts of differing sizes via interchangeable breast centering rings, which provide circular openings or apertures of differing diameters, all centered on the centerline of the scanning chamber.  
           [0005]    In such a computed-tomography geometry, it is required that the rotational centerline of the scanning mechanism pass through the object being scanned. Otherwise the laser beam does not impinge upon the object, and no optical transmission data can be obtained. While this constraint is easily met when the scanner is high in the breast, near the chest wall, the breast will likely move off the rotational centerline, as the scan progresses down the breast toward the nipple. Breasts are generally not conical in shape, typically being quite asymmetric from top to bottom, and somewhat asymmetric from left to right. Typically, even with a prone patient, the breast extends further above the nipple than below. The sagging caused by gravity is permanent, even in the prone position.  
         OBJECTS AND SUMMARY OF THE INVENTION  
         [0006]    It is an object of the present invention to provide a non-circular opening in the tabletop of the (prone) patient support structure such that more of the patient&#39;s breast will remain on the rotational centerline of the sensors and radiation beam.  
           [0007]    It is another object of the present invention to provide a method for positioning a patient&#39;s breast vertically pendant below a tabletop and disposed within a scanning chamber below the tabletop having a scanning mechanism rotating about vertical axis of rotation such that the lowest portion of the breast intersects with the axis of rotation of the scanning mechanism.  
           [0008]    It is still another object of the present invention to provide a scanning apparatus, comprising a support structure including a tabletop to support a female patient in front-down, prone position with an opening in which a breast of the patient is vertically pendant below the tabletop and a detector array that rotates around the breast about a vertical axis disposed asymmetrically through the opening such that the axis intersects a bottom portion of the pendant breast.  
           [0009]    In summary, the present invention provides a patient support structure for a laser imaging apparatus, comprising a tabletop to support a female patient in front-down, prone position. The tabletop includes an opening adapted to permit a breast of the patient to be vertically pendant below the tabletop. The opening is non-symmetric with respect to an axis of rotation of a scanning mechanism disposed below the tabletop.  
           [0010]    The present invention also provides a method for positioning a patient&#39;s breast vertically pendant below a tabletop and disposed within a scanning chamber below the tabletop having a scanning mechanism rotating about vertical axis of rotation. The method comprises positioning the breast within the scanning chamber such that its lowest portion intersects with the axis of rotation of the scanning mechanism.  
           [0011]    The present invention further provides a scanning apparatus, comprising a support structure including a tabletop to support a female patient in front-down, prone position. The tabletop has an opening adapted to permit a breast of the patient to be vertically pendant below the tabletop. A detector array to image the internal structure of the breast is disposed below the tabletop and includes a laser beam directed toward the breast and a plurality of detectors disposed in an arc around the opening to detect the laser beam after passage through the breast. The detector array is rotatable about a vertical axis disposed asymmetrically through the opening such that the axis intersects a bottom portion of the pendant breast.  
           [0012]    These and other objects of the present invention will become apparent from the following detailed description. 
       
    
    
     BRIEF DESCRIPTIONS OF THE DRAWINGS  
       [0013]    [0013]FIG. 1 is a schematic side elevational view of a scanning apparatus with a planar detector array, showing a prone patient positioned for optical tomographic study, with one breast pendant through a scanning aperture and disposed within the scanning chamber.  
         [0014]    [0014]FIG. 2 is a schematic top view of the scanning apparatus of FIG. 1, showing a circular scanning aperture.  
         [0015]    [0015]FIG. 3 is a schematic top view of the scanning chamber of FIG. 1, showing the planar detector array, consisting of a plurality of detectors disposed around an object being scanned and a laser light source.  
         [0016]    [0016]FIGS. 4A and 4B are schematic cross-sectional views through the planar detector array of FIG. 3, showing the laser light source and detectors and the breast pendant in the scanning chamber through a circular scanning aperture, with the scanning plane at two different positions on the breast.  
         [0017]    [0017]FIG. 5 is a schematic top view of the scanning apparatus of FIG. 1, showing a non-circular scanning aperture superimposed over the circular scanning aperture of FIG. 2.  
         [0018]    [0018]FIGS. 6A and 6B are schematic cross-sectional views through the planar detector array of FIG. 3, showing the laser light source and detectors and a breast pendant in the scanning chamber through the non-circular scanning aperture of FIG. 5, with the scanning plane at two different positions on the breast.  
         [0019]    [0019]FIG. 7 shows a detailed view of the asymmetric and non-circular aperture of FIG. 5.  
         [0020]    [0020]FIG. 8 is a schematic top view of the scanning apparatus of FIG. 1, showing a non-circular scanning aperture disposed in a removable centering disk.  
         [0021]    [0021]FIG. 9 is schematic cross-sectional view along line  9 - 9  of FIG. 8.  
         [0022]    [0022]FIG. 10 shows a plurality of centering disks, each one having a different sized scanning aperture. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0023]    Referring to FIG. 1, a scanning apparatus  2 , as described in U.S. Pat. Nos. 5,692,511 and 6,100,520, supports a prone patient  4  face down on a support structure  3  having an essentially flat tabletop  6 . The patient&#39;s breast  8  is pendant within a scanning chamber  10 , around which orbits a planar detector array  12 . The planar detector array  12  orbits typically 360° around the vertical axis of the scanning chamber  10  and increments vertically downward between orbits to image successive slice planes of the breast. This is repeated until all the slice planes of the breast have been scanned.  
         [0024]    Referring to FIG. 2, a top view of the scanning apparatus  2  from FIG. 1 is shown. The patient  4  lies on the tabletop  6  with her breast through a circular scanning aperture  14 . The patient is shown positioned for a scan of her left breast and would move to her left for a scan of her right breast.  
         [0025]    Referring to FIG. 3, a top view of the planar detector array  12  is shown. The laser source  16  impinges on the scanned breast  8  at point  18 . A plurality of detectors  20  defines an arc surrounding the breast. A collimator  22  defines each detector&#39;s field of view to a small area on the surface of the breast. Light enters the scanned object at point  18  and exits at every point on its circumference, such as at exit points  24 ,  26  and  28  corresponding to three detectors. The entire mechanism rotates, as indicated by the curved arrow  32 .  
         [0026]    Every detector  20  is collimated, aiming at the center of orbit rotation  30  and the laser source  16  also points toward the center of rotation. The detectors  20  are spaced at equal angular increments around the center of rotation. The orbit rotation is alternately 360° clockwise for one (horizontal) slice plane, then 360° counterclockwise for the next slice plane.  
         [0027]    Referring to FIG. 4A, a vertical cross-section through the planar detector array of FIG. 3 is shown. The planar detector array  12  is shown as imaging one slice, though any number of slices can be imaged simultaneously as disclosed in U.S. Pat. No. 6,100,520. The patient&#39;s breast  8  is pendant within the scanning chamber  10 , with the rotational centerline  30 . The patient is supported by the tabletop  6 . The circular scanning aperture  14  in the tabletop  6 , defined by points  34  and  36 , is shown as symmetric about the rotational centerline  30 . The laser source  16  projects a coherent light beam  38  which impinges on the patient&#39;s breast  8  at point  40 . A detector assembly  41  (one of a plurality as shown in FIG. 3) receives the light emitted from the patient&#39;s breast at  42 . The detector assembly consists of the collimator  22 , shown as an opaque body  43  with a collimating channel  44 . The collimating channel can be round, square, hexagonal, triangular or any other cross-sectional shape. The collimator restricts the field of view of each detector assembly to a small, defined area on the surface of the scanned breast. At the rear of each collimating channel is a lens  46 , which focuses the light propagating down the collimating channel onto the photodetector  20 . The lenses are shown as plano-convex, but could be biconvex or could be eliminated if the photodetector&#39;s area were larger than the collimating channel&#39;s area. The photodetector is connected to a signal processing electronics board  32 , which would typically provide amplification and analog-to-digital conversion.  
         [0028]    The laser source  16  could be a semiconductor diode laser, a solid-state laser or some other near-infrared light source. The photodetectors  20  could be photodiodes, avalanche photodiodes, phototransistors, photomultiplier tubes, microchannel plates or some other photosensitive device that converts incoming light photons to an electrical signal.  
         [0029]    The detector assembly  41  is shown in FIG. 4A to be positioned at its highest point, nearest the patient&#39;s chest wall. The slice plane, defined by points  40  and  42 , is as high as possible, the nominal starting point of the scan. Referring to FIG. 4B, the same detector assembly  41  is shown later in the scan, having moved downward, away from the chest wall. The laser source  16  is fixed relative to the detector assembly  41 , such that it moves with the detector assembly during rotation around the breast and when it increments vertically. In other words, the laser source  16  or the laser beam  38  moves synchronously with the detector assembly  41  vertically and around the breast.  
         [0030]    Because of the asymmetry of the breast, the laser beam  38  will miss the breast  8  entirely at some portion of the 360° orbit, as shown in FIG. 4B. The slice data is only valid if the laser beam  38  contacts the breast during the entire 360° orbit. At the level of the slice plane, defined by points  52  and  54 , the rotational centerline  30  of the scanning chamber  10  no longer passes through the breast  8 , which means that the laser beam  38  will not pass through the breast at some point in the rotation of the laser source  16  and the detector assembly  41 . The scan cannot continue any lower on the breast as a consequence, since the scan is programmed to shut down when the beam  38  impinges on the detector  20  without passing through the breast.  
         [0031]    A top view of the scanning apparatus  2  is shown in FIG. 5 with an asymmetric non-circular scanning aperture  56  in the tabletop  6 . The aperture  56  is disposed non-symmetrically with respect to the axis of rotation  30  to provide more space on the side of the rotational centerline  30  toward the patient&#39;s head as compared to the circular aperture  14  (see FIG. 2). Part of the original circular aperture  14  is shown with a dashed line  58 .  
         [0032]    The detector assembly  41  positioned at its highest point, nearest the patient&#39;s chest wall, is shown in FIG. 6A. The asymmetric scanning aperture  56 , defined by points  60  and  62 , allows more space above the rotational centerline  30  of the scanning chamber  10  for the breast  8  toward the patient&#39;s head. In FIG. 6B, the detector assembly  41  and the laser source  16  have moved downward and the rotational centerline  30  is still within the breast, which means that the slice data is valid. The laser beam  38  impinges the breast at points  64  and  66 , thereby still allowing the laser beam to penetrate the breast, as compared to FIG. 4B where the laser beam would not pass through the breast at some point in the orbit of the detector assembly. The asymmetric scanning aperture  56  permits the axis of rotation  30  to pass through the lowest portion  67  of the breast, thereby allowing the laser beam  38  not to miss the lower portion of the vertically pendant breast.  
         [0033]    The preferred embodiment of the asymmetric scanning aperture  56  is shown in greater detail in FIG. 7. The scanning aperture  56  is defined with respect to the rotational centerline  30 . An inferior portion  68  is bounded on one side of an imaginary line  69  extending across the aperture and intersecting the axis of rotation  30  and a peripheral edge  71  of the aperture extending toward the patient&#39;s feet. The inferior portion has a radius  70 . A superior portion  72  is bounded by the opposite side of the imaginary line  69  and peripheral edge  73  extending from the imaginary line  69  toward the patient&#39;s head. The superior portion  72  has a radius  74  greater than the radius  70 . The dotted line  76  shows the continuation of the radius  70  to illustrate the additional space  76  provided by the superior portion  72  of the aperture as compared to the circular aperture  14 . The two radii are connected by tangents  78  to radius  70  with fillets  80  and  82  at the intersections of the tangents  78  with the radius  74 . The inferior portion  68  is seen to semi-circular, while the superior portion  72  includes a circular arc.  
         [0034]    The scanning aperture  56  can be built into the tabletop  6 . However, it is preferable to implement the aperture  56  with a removable centering disk  84  which fits into a cooperating recess  86  in the tabletop  6 , as best shown in FIGS. 8 and 9. The tabletop  6  has an opening  88  which is smaller than the outside diameter of the disk  84 , thereby providing a flange portion  87  to support the disk. The disk  84  preferably has a circular outer shape. Since the disk  84  is removable, several disks may be provided, each disk having a different size aperture shape, so that the proper size aperture can be chosen that best fits a particular patient, as generally shown in FIG. 10.  
         [0035]    Although a specific shape has been disclosed for the aperture, other shapes could be employed, such as ellipses, ovals, race-track shapes, etc and disposed asymmetrically with respect to the axis of rotation  30 . The peripheral edge portion  90  of the scanning aperture  56  can be made pliable to better accommodate the patient.  
         [0036]    While this invention has been described as having preferred design, it is understood that it is capable of further modification, uses and/or adaptations following in general the principle of the invention and including such departures from the present disclosure as come within known or customary practice in the art to which the invention pertains, and as may be applied to the essential features set forth, and fall within the scope of the invention or the limits of the appended claims. We claim:

Technology Classification (CPC): 0