Abstract:
A scanner for a laser imaging apparatus comprises a tabletop having an opening in which a breast to be scanned is disposed; a reflector ring disposed around the opening below the tabletop, the ring having a reflective surface facing the opening and disposed at an angle downwardly away from the opening; a laser beam directed upwardly below the tabletop toward the reflective surface such that the beam is reflected across the opening toward an opposite portion of the reflective surface, the beam going across the opening defining a slice plane; a plurality of collimators including vertical channels directed toward the reflective surface such that light exiting from the breast within the field of view of the collimators is reflected by the reflective surface down through the vertical channels; a plurality of optical detectors, each detector being disposed below the respective vertical channels. The laser beam, collimators and detectors are adapted to be orbited at the same time around the breast about an orbital axis through the opening. Each of said detectors is configured to simultaneously detect light exiting the breast being scanned within the respective field-of-view of each collimator.

Description:
RELATED APPLICATIONS  
       [0001]    This application claims the benefit of U.S. Provisional Application Serial No. 60/466,062, filed Apr. 29, 2003, hereby incorporated by reference. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates generally to a diagnostic medical imaging apparatus that employs a near-infrared laser as a radiation source and a detector array with restricted fields of view directed to their own patches of surface of the object being scanned to simultaneously detect the intensity of light exiting from the object for the purpose of reconstructing cross-sectional images of the object, and more particularly to folded optics in such a laser imaging apparatus with an ergonometric tabletop.  
         BACKGROUND OF THE INVENTION  
         [0003]    Cancer of the breast is a major cause of death among the American female population. Effective treatment of this disease is most readily accomplished following early detection of malignant tumors. Major efforts are presently underway to provide mass screening of the population for symptoms of breast tumors. Such screening efforts will require sophisticated, automated equipment to reliably accomplish the detection process.  
           [0004]    The x-ray absorption density resolution of present photographic x-ray methods is insufficient to provide reliable early detection of malignant tumors. Research has indicated that the probability of metastasis increases sharply for breast tumors over 1 cm in size. Tumors of this size rarely produce sufficient contrast in a mammogram to be detectable. To produce detectable contrast in photographic mammograms 2-3 cm dimensions are required. Calcium deposits used for inferential detection of tumors in conventional mammography also appear to be associated with tumors of large size. For these reasons, photographic mammography has been relatively ineffective in the detection of this condition.  
           [0005]    Most mammographic apparatus in use today in clinics and hospitals require breast compression techniques which are uncomfortable at best and in many cases painful to the patient. In addition, x-rays constitute ionizing radiation which injects a further risk factor into the use of mammographic techniques as most universally employed.  
           [0006]    Ultrasound has also been suggested as in U.S. Pat. No. 4,075,883, which requires that the breast be immersed in a fluid-filled scanning chamber. U.S. Pat. No. 3,973,126 also requires that the breast be immersed in a fluid-filled chamber for an x-ray scanning technique.  
           [0007]    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 tomography to the brink of clinical usefulness. Optical wavelength photons do not penetrate in vivo tissue is a straight line as do x-ray photons. This phenomenon causes the light photons to scatter inside the tissue before the photons emerge out of the scanned sample.  
           [0008]    Because x-ray photon propagation is essentially straight-line, relatively straight forward techniques based on the Radon transform have been devised to produce computed tomography images through use of computer algorithms. Multiple measurements are made through 360° around the scanned object. These measurements known as projections are used to backproject the data to create an image representative of the interior of the scanned object.  
           [0009]    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 a extremely low level and requires sophisticated techniques to capture the low level signals.  
           [0010]    U.S. Pat. No. 5,692,511 discloses such a laser imaging apparatus. In this apparatus, the detector housings (collimators) are perpendicular to the orbit axis, therefore parallel to the patient&#39;s chest wall. The detector housings (collimators) for any given slice lie in a plane, the optical plane or slice plane. The detector array is consequently “planar”.  
           [0011]    The use of a planar detector array dictates that the patient support surface (the tabletop) surrounding the breast be planar, flat. However, a more desirable patient support surface would allow vertical relief for the patient&#39;s shoulder, arms, other breast and head to provide comfort to the patient during scanning.  
         OBJECTS AND SUMMARY OF THE INVENTION  
         [0012]    It is an object of the present invention to provide a scanner structure that accommodates the raised and lowered support surfaces that support a patient&#39;s other body portions while her breast or other body portion is being scanned.  
           [0013]    It is another object of the present invention to provide a scanner that uses folded optics to allow placement of the laser and the detectors some distance below the raised surfaces of the tabletop and yet allow scanning of the breast adjacent the raised surfaces.  
           [0014]    It is a further object of the present invention to provide contiguous arrays of sensors around a scanned object wherein the sensors have a field of view restricted to the volume within a single slice plane and the sensors and radiation beam are translated to parallel slice planes, contiguous or separated, through a scanned object, with the scan planes being offset from the radiation beam plane.  
           [0015]    It is another object of the present invention to provide one or more sensors positioned in a circle or arc around a scanned object that allow simultaneous acquisition of photon intensity data on the surface of a scanned object illuminated by one or more radiation beams while the sensors and radiation beam are rotated around the scanned object and the scan slice planes are offset from the radiation beam plane.  
           [0016]    It is another object of the present invention to provide one or more sensors positioned in a circle or arc around a scanned object that allow simultaneous acquisition of photon intensity data on the surface of a scanned object illuminated by one or more radiation beams while the sensors and radiation beam are at one fixed location and the scan slice planes are offset from the radiation beam.  
           [0017]    It is still another object of the present invention to provide a plurality of detectors to acquire photon transport data from tissue within multiple parallel planes separated by thicknesses to form multiple slices of a total volume.  
           [0018]    It is another object of the present invention to provide a plurality of sensors to acquire photon transport data from tissue within multiple parallel planes separated by thicknesses to form slices of a total volume to reconstruct a 3-dimensional image of the interior of the scanned volume.  
           [0019]    It is another object of the present invention to provide contiguous arrays of sensors around a scanned object and wherein the sensors have a field of view restricted to the volume within a single slice plane while the sensors and radiation beam are at one fixed point with respect to the scanned object.  
           [0020]    It is another object of the present invention to provide contiguous arrays of sensors around a scanned object and wherein the sensors have a field of view restricted to the volume within a single slice plane while the sensors and radiation beam are rotated around the scanned object.  
           [0021]    In summary, the present invention provides a scanner for a laser imaging apparatus, comprising a tabletop having an opening in which a breast to be scanned is disposed; a reflector ring disposed around the opening below the tabletop, the ring having a reflective surface facing the opening and disposed at an angle inclined toward the opening; a laser beam originating below the tabletop and directed upwardly toward the reflective surface such that the beam is reflected across the opening toward an opposite portion of the reflective surface, the beam going across the opening defining a slice plane; a plurality of collimators including vertical channels directed toward the reflective surface such that light exiting from the breast within the field of view of the collimators is reflected by the reflective surface down through the vertical channels; a plurality of optical detectors, each detector being disposed below the respective vertical channels. The laser beam, collimators and detectors are adapted to be orbited at the same time around the breast about an orbital axis through the opening. Each of said detectors is configured to simultaneously detect light exiting the breast being scanned within the respective field-of-view of each collimator.  
           [0022]    These and other objectives of the present invention will become apparent from the following detailed description. 
       
    
    
     BRIEF DESCRIPTIONS OF THE DRAWINGS  
       [0023]    [0023]FIG. 1 is a schematic side elevational view of a scanning apparatus with a planar detector array configuration, showing a prone patient positioned for an optical tomographic study, with one breast pendent within the scanning chamber.  
         [0024]    [0024]FIG. 2 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.  
         [0025]    [0025]FIG. 3 is a schematic cross-sectional view through the planar detector array of FIG. 2, showing the laser light source and the detectors.  
         [0026]    [0026]FIG. 4 is a schematic side elevational view of a scanning apparatus with a tabletop having vertical relief around the breast and showing a prone patient positioned for an optical tomographic study, with one breast pendent within the scanning chamber.  
         [0027]    [0027]FIG. 5A is a perspective top view of the scanning apparatus of FIG. 4, showing the tabletop with vertical relief around the breast and the scanning chamber.  
         [0028]    [0028]FIG. 5B is a top plan view of FIG. 5A.  
         [0029]    [0029]FIG. 6 is a block diagram of the data acquisition system that supports the detector array of FIGS. 2 and 3.  
         [0030]    [0030]FIG. 7 is a cross-sectional view through the folded-optics detector array of FIG. 4, showing the laser light source, a conical folding mirror and detectors for two slices.  
         [0031]    [0031]FIG. 8 is a cross-sectional view through the folded-optics detector array of FIG. 4, showing the laser light source, a conical folding mirror and detectors for five slices.  
         [0032]    [0032]FIG. 9 is a cross-sectional view through the folded-optics detector array of FIG. 4, showing the laser light source, a conical folding prism and detectors for two slices.  
         [0033]    [0033]FIG. 10 is a cross-sectional view through the folded-optics detector array of FIG. 4, showing the laser light source and detectors for two slices, employing optic fibers to achieve the folding function. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0034]    Referring first 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  on an essentially flat top surface  6 . The patient&#39;s breast  8  is pendent 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 between orbits to image successive slice planes. This is repeated until all the slice planes of the breast have been scanned. Since the surface  6  is a single level, flat surface, the patient&#39;s head and shoulder tend to contact the table surface, causing discomfort and lifting the breast somewhat out of the scanning chamber.  
         [0035]    [0035]FIG. 2 shows a top view of the planar detector array  12  from FIG. 1. A laser source  14  generates a laser beams that impinges on the scanned object (breast)  8  at a point  16 . A plurality of detectors  18  defines an arc surrounding the scanned object. A collimator  20  defines each detector&#39;s field of view to a small area on the surface of the scanned object. Light enters the scanned object at point  16  and exits at every point on its circumference. Three exit points  22 ,  24  and  26  are shown, corresponding to three detectors. The entire mechanism rotates around the center-of orbit rotation  28 , as indicated by the curved double-headed arrow  30 .  
         [0036]    In the preferred implementation, every detector in the array is collimated, aiming at the center of orbit rotation  28 . The laser source also points toward the center of rotation. The detectors are spaced at equal angular increments around the center of rotation. The orbit rotation is preferably alternately 360° clockwise for one (horizontal) slice plane, and 360° counterclockwise for the next slice plane.  
         [0037]    [0037]FIG. 3 shows a vertical cross-section through the planar detector array  12  of FIG. 2. The planar detector array  12  is shown as simultaneously imaging two adjacent slices  32  and  34 , 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 pendent within the scanning chamber  10 . The patient is supported by the scanning apparatus&#39; tabletop surface  6 . The laser  14  projects a coherent light beam  36  which impinges on the patient&#39;s breast at point  38 .  
         [0038]    Two photodetectors  40 , one each from the two slice planes  32  and  34 , are shown imaging points  42  and  44  on the breast for the upper and lower slices, respectively. The opaque collimator  20  is shown as a single physical entity with two collimating channels  46 . The collimating channels  46  can be round, square, hexagonal, triangular or any other cross-sectional shape. The collimator  20  advantageously restricts the field of view of each detector assembly to a small, defined area on the surface of the scanned object. At the rear of each collimating channel is a lens  48 , which focuses the light propagating down the collimating channel onto the photodetector  40 . The lenses are shown as plano-convex, but can be biconvex or can be eliminated if the photodetector&#39;s active area were larger than the collimating channel&#39;s-cross-sectional area. The photodetectors are connected to a signal processing system  50  for amplification and analog-to-digital conversion.  
         [0039]    The laser  14  can be a semiconductor diode laser, a solid-state laser or any other near-infrared light source. The photodetectors  40  can be photodiodes, avalanche photodiodes, phototransistors, photomultiplier tubes, microchannel plates or any other photosensitive device that converts incoming light photons to an electrical signal. The photodetectors provide the means for detecting the laser beam after passing through the breast.  
         [0040]    [0040]FIG. 4 shows a schematic side elevational view of a scanning apparatus  52  with a tabletop surface  54  shaped so as to allow vertical relief for the patient&#39;s shoulder, arms, head and opposite breast. A prone patient  4  is positioned for an optical tomographic study, with one breast  8  pendent within a scanning chamber  56 . A folded-optics detector array  58 , shown schematically, orbits typically 360° around the vertical orbital axis of the scanning chamber  56  and increments vertically downward between orbits to image successive slice planes. This is repeated until all the slice planes of the object have been scanned.  
         [0041]    The tabletop surface  54  has a lower level surface  60  and a higher level surface  62 . The lower level surface  60  advantageously provides relief and support for the patient&#39;s shoulder, arms, head and opposite breast. The higher level surface  62  advantageously provides support for the patient&#39;s lower body and legs.  
         [0042]    [0042]FIG. 5A shows the scanning apparatus tabletop  54  in perspective. The patient&#39;s breast  8  would be pendent in the scanning chamber  56 . The patient&#39;s torso and legs are supported by the surface  62 , which is advantageously at the same level as the opening  64  of the scanning chamber  56 . The surface  60  supports the patient&#39;s head, advantageously allowing the head to be positioned below the top of the scanning chamber for comfort. Assuming the patient&#39;s left breast is positioned in the scanning chamber  56 , surface  66  advantageously provides relief for the patient&#39;s right breast and surface  68  provides relief for the patient&#39;s left shoulder and a resting place for the patient&#39;s left arm. The roles of the surfaces  66  and  68  are reversed for scanning the right breast. The tabletop  54  is preferably symmetrical in plan-view, as shown in FIG. 5B.  
         [0043]    Surfaces  60 ,  66  and  68  are at the same level in the preferred embodiment, approximately 7 centimeters below the rim of the scanning chamber  56 . However, it should be understood that these surfaces can be at different levels. A transition surface  70  between the higher level surface  62  and the lower level surfaces  60 ,  66  and  68  is preferably slanted or ramped to provide room underneath for the detector array  58 . The surface  62  preferably tapers toward the opening  64 . The transition surface  70  also provides support for parts of the patient&#39;s body immediately adjacent the breast being scanned. A horizontal flange or lip  71  around the opening  64  provides further comfortable support to the peripheral base area of the breast being scanned.  
         [0044]    The preferred embodiment has the patient lying prone with the breast pendent in the scanning chamber. Although the tabletop is shown horizontal for a patient in prone position, it should be understood that the tabletop can be in any position.  
         [0045]    [0045]FIG. 6 shows the signal processing system  50 . A plurality of photodetectors  40  are connected to a plurality of amplifiers  72 . In the preferred embodiment, the photodetectors are photodiodes and the amplifiers are integrators. The amplifiers are connected to a multiplexer (MUX)  74  which presents one of “N” amplifier outputs to an analog-to-digital converter (ADC)  76 . The digital output of the ADC is connected to an image processor  78 , typically a general-purpose computer. The image processor performs the reconstruction computations to create cross-sectional images from the projection data collected by the scanning apparatus. Multiple MUXes and ADCs can be employed in order to decrease the data acquisition time.  
         [0046]    [0046]FIG. 7 shows a detailed vertical cross-sectional view along line  7 - 7  of FIG. 5 of the folded-optics detector array  58  shown schematically in FIG. 4. The folded-optics detector array is shown as simultaneously imaging two adjacent slices, the preferred embodiment, though any number of slices can be imaged simultaneously, such as five slices shown in FIG. 8. The patient&#39;s breast  8  is pendent within the scanning chamber  56 . The patient is supported by the scanning apparatus&#39; tabletop  54 . The lower surfaces  66  and  68  are shown supporting the patient&#39;s left shoulder and the right breast (the left breast is shown within the scanning chamber). The laser  14  projects a coherent light beam  36  which impinges on the patient&#39;s breast at point  80  after reflecting from a planar turning mirror  82  and a conical mirror  84 . The planar turning mirror  82  is commonly used. The conical mirror  84  is a ring around the scanning chamber  56  and is a segment, a frustum of a hollow cone with the inside 45° conical surface  85  being reflective. The same conical mirror  84  reflects light emitted from the breast at points  88  and  90  into “N” number of two-detector assemblies  92 , which detect light coming from the upper and lower slices, respectively. The detector assemblies  92  are arranged in a circle or arc, with their longitudinal axes through the vertical channels all pointing upwards toward the conical mirror  84 . The slanting surface  70  advantageously provides room for the conical mirror  84  and the collimators  94 .  
         [0047]    The conical mirror  84 , in the preferred embodiment, is a diamond-turned aluminum mirror with a high-reflectivity gold plating on the inside conical surface  85 . Alternatively, it can be polished glass or plastic with a reflective coating, or any other reflective material capable of being formed into a conical shape. The laser turning mirror  82  can be eliminated with the laser  14  projecting vertically onto the conical mirror  84 .  
         [0048]    The detector assemblies  92  consist of an opaque collimator  94 , shown as a single physical entity with two collimating channels  96  and  98 . The collimating channels are folded 90° at  99  by the conical mirror  84  and actually intersect each other, forming horizontal and vertical channels. The intersecting collimating channels, which allow the light to intersect, are not of concern, since light at these power levels, in air, does not interact with itself. There is no interference between the light from areas  88  and  90  although their paths cross. The collimating channels can be round, square, hexagonal, triangular or an other cross-sectional shape. The collimator restricts the fields of view of each detector assembly to a small, defined area on the surface of the breast  8 , the scanned object.  
         [0049]    At the rear or bottom of each vertical collimating channel is a lens  100 , which focuses the light propagating down the collimating channel onto the photodetector  102  located below the exit ends of the vertical channels. The lenses are shown as plano-convex, but can be biconvex or can be eliminated if the photodetector&#39;s active area were larger than the collimating channel&#39;s cross-sectional area. The photodetectors  102  are connected to the signal processing system  50 , providing amplification and analog-to-digital conversion, as shown in FIG. 6.  
         [0050]    The laser  14  and photodetectors  102  are the same as described for the planar detector configuration.  
         [0051]    [0051]FIG. 8 shows a five-detector assembly  106 , using the conical mirror  84  of FIG. 7. The laser  14  projects a coherent light beam  36  which impinges on the patient&#39;s breast  8  after reflecting from the planar turning mirror  82  and the conical mirror  84 . The same conical mirror  84  reflects light emitted from the breast at points  108 ,  110 ,  112 ,  114  and  116  into “N” number of the five-detector assemblies  106 , advantageously allowing the simultaneous imaging of five consecutive slices. The detector assemblies  106  are arranged in a circle or arc around the scanning chamber  56 . It should be understood that the horizontal channels form a series of arcs around the opening of the scanning chamber, each arc being disposed vertically below the topmost arc. It should also be understood that the vertical channels similarly form a series of arcs around the opening, where each arc is larger than an adjacent arc nearer to the opening.  
         [0052]    [0052]FIG. 9 shows an alternative to the conical mirror  84  for folding the optical path of both the laser beam  36  and the detectors  102 . The laser  14  projects a coherent light beam  36  which impinges on the patient&#39;s breast  8  at  118  after reflecting from the planar turning mirror  82  and a conical prism  120 . The conical prism  120  is a ring around the scanning chamber  56  and is a right triangle swept into a circle. Its outside surface  121  is preferably conical; its inside surface  123  is preferably cylindrical. Its cross-section is the classic 45° prism, which reflects light 90° by total internal reflection. The same conical prism  120  reflects light emitted from the breast at points  124  and  126  into “N” number of two-detector assemblies  92  imaging the upper and lower slices, respectively. The detector assemblies are arranged in a circle or arc, with the longitudinal axes of the vertical collimator channels all pointing upwards toward the conical prism  120 . The prism  120  may be made of optical glass, sapphire, quartz, various plastics or any other material with a high transmission of near-infrared light.  
         [0053]    [0053]FIG. 10 shows an alternative to the conical mirror  84  or the prism  120  for folding the optical path of both the laser and the detectors. The laser  14  projects a coherent light beam  36  which is coupled by lens  128  into an optical source fiber  130 . Lens  132  collimates the light from the source fiber  130  and projects a parallel beam  134  which impinges on the breast at point  136 . Light emitted from the breast at points  138  and  140  is focused into optical detector fibers  142  by lenses  144 . The detector fibers  142  receive the light at their entry ends and conduct the light to detectors  146  located near their exit ends. Additional lenses may be interposed between the detector fibers  142  and the detectors  146 , depending on the relative size of the optical fiber and detector. Lens  128  may be eliminated depending on the relative size of the optical fiber  130  and the beam diameter from the laser  14 . Lenses  132  and/or  144  may be eliminated, depending on the size and numerical aperture of the optical fibers and their proximity to the breast. It should be understood that the entry ends of the optic fibers  142  form a series of arcs around the opening, where each arc is disposed below the topmost arc.  
         [0054]    A number of planar mirrors can be employed alternatively to the conical mirror  84 , with the mirrors all at 45° and butted end-to-end forming an “N”-sided polygon. The more mirrors are used, the closer the approximation would be to the single-piece conical mirror. Similarly, a number of 45° prisms, butted end-to-end to form a polygonal ring, can be used in place of the single conical prism.  
         [0055]    The mirror or the prism alters the light paths from the breast from the horizontal scan plane to the vertical longitudinal axes of the detector assemblies. The “folding angle” is disclosed as 90°, but it should be understood that other folding angles can be employed. Further, the scan plane need not be horizontal and the orbital axis vertical. In an optical scanner used for head imaging, for example, the scan plane can be vertical, or nearly so, with an essentially horizontal orbital axis. It should also be understood that the mirrors, prism or the optic fibers provide the means for folding and directing the laser beam across the opening from a location below the scan plane.  
         [0056]    The various collimators disclosed provide the means for restricting the field-of-view of each photodetector to a small area on the surface of the breast.  
         [0057]    While this invention has been described as having a preferred design, it is understood that it is capable of further modification, uses and/or adaptations of the invention 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.