Abstract:
An apparatus for breast scanning to obtain functional and anatomical images of the breast comprises a patient support for a patient to rest in a prone position, the support having an opening with one of her breasts vertically pendent through the opening for scanning; a laser CT scanner disposed below the support for generating a first set of data for reconstruction of functional images of the breast; an X-ray CT scanner disposed below the support for generating a second set of data for reconstruction of anatomical images of the breast; and a display to visualize at least one of the functional and anatomical images. A method for acquiring data for reconstruction of images pertaining to functional and anatomical structures of a breast comprises positioning a patient in a prone position on a support having an opening through which a breast of the patient is pendant; scanning the breast with a laser CT scanner to obtain data of the breast for functional image reconstruction of the breast; and while the patient is still prone on the support, scanning the breast with an X-ray CT scanner to obtain data of the breast for anatomical image reconstruction of the breast.

Description:
RELATED APPLICATIONS  
       [0001]     This is a nonprovisional application, which claims the priority benefit of provisional application Ser. No. 60/718,307, filed Sep. 20, 2005, herein incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     It is vital to be able to detect cancers in the breast at their early stage. Moreover, it is very important to discern malignant from benign lesions. For biopsy and surgery purposes, it is essential to know the location and the extent of the lesion. For therapeutic purposes, it is useful to track tumor response to neoadjuvant and radiation therapy.  
         [0003]     Current commercial scanners or medical diagnostic equipments available in the market provide only partial solutions to the above goals. For instance, it is current practice to use mammography to detect tumors. A major drawback of this imaging modality is that each pixel of a mammography image represents a ray sum of attenuation coefficients of the tissue along the ray. Therefore, the 3D location of the tumor or the depth effect is lost. The compression employed in mammography causes pain and disturbs the breast, making it difficult to determine biopsy sites and has the risk of potentiating the metastatic spread of cancer. This deficiency may be overcome by using ordinary CT scanners. Unfortunately, a much higher x-ray dose to the patient compared to that of mammography is inherent in the conventional CT scans. To address the issues on overdosing the patient, J. Boone et al. (Radiology, 221, 657-667, 2001), have conducted extensive studies on using the x-ray cone beam CT technology with a special positioning of the patient in order to expose x-ray to the breast area only.  
         [0004]     At this point, it is worth noting that both the x-ray mammography and CT modalities may be able to detect a lesion inside the breast, but neither of them is able to distinguish benign from malignant lesions. The distinction between these lesions could be based on the angiogenesis. Current development of CT scanners by Imaging Diagnostic Systems, Inc. (U.S. Pat. Nos. 5,692,511; 6,130,958 and 6,211,512), using a laser energy source instead of x-ray have shown the capability of providing a map of the blood supply (hemoglobin), which is present to feed the lesion. This extremely useful information suffers from the limited spatial resolution caused by the scatter effect of the laser while penetrating inside the breast, and the aberration effect due to the non linear photon migration path. To improve the limited resolution of such imaging system and to speed up the computational reconstruction time, Kawaguchi et al. (U.S. Pat. No. 5,419,320) suggested generating functional images based on an x-ray CT scan of the same anatomy. This method relies on an initial estimate of the functional images using the standard values of physical quantities of the corresponding anatomical structures identified by an image segmentation of the x-ray CT images. The final functional images are computed iteratively to match the optical data collected during the laser scan. One disadvantage of this method is that it would not be possible to generate functional images without the availability of the corresponding anatomical images from the x-ray scan. Moreover, an estimate of a functional image from an anatomical image is not reliable. This could affect the convergence of the algorithm, and may lead to a false functional image.  
       OBJECTS AND SUMMARY OF THE INVENTION  
       [0005]     It is an object of the present invention to provide an apparatus for providing functional and anatomical images of the breast for cancer screening and diagnosis.  
         [0006]     It is another object of the present invention to provide an apparatus for generating images of the anatomical structure of the breast with minimal dose to the patient to be an effective screening tool for breast cancer detection.  
         [0007]     It is still another object of the present invention to provide an apparatus for providing functional and anatomical images of the breast that are correlated to provide complementary information for screening and diagnosis of breast cancer.  
         [0008]     It is an object of the present invention to provide an apparatus for providing functional and anatomical images of the breast that provide independent scanning with laser and X-ray to complete a scan relatively quickly to minimize patient motion.  
         [0009]     It is another object of the present invention to provide an apparatus for providing functional and anatomical images of the breast using laser and X-ray scanners with independent image reconstruction.  
         [0010]     In summary, the present invention provides an apparatus for breast scanning to obtain functional and anatomical images of the breast, comprising a patient support for a patient to rest in a prone position, the support having an opening with one of her breasts vertically pendent through the opening for scanning; a laser CT scanner disposed below the support for generating a first set of data for reconstruction of functional images of the breast; an X-ray CT scanner disposed below the support for generating a second set of data for reconstruction of anatomical images of the breast; and a display to visualize at least one of the functional and anatomical images.  
         [0011]     The present invention also provides a method for acquiring data for reconstruction of images pertaining to functional and anatomical structures of a breast, comprising positioning a patient in a prone position on a support having an opening through which a breast of the patient is pendant; scanning the breast with a laser CT scanner to obtain data of the breast for functional image reconstruction of the breast; and while the patient is still prone on the support, scanning the breast with an X-ray CT scanner to obtain data of the breast for anatomical image reconstruction of the breast.  
         [0012]     These and other objects of the present invention will become apparent from the following detailed description. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]      FIG. 1  is a block diagram of a scanning apparatus made in accordance with the present invention.  
         [0014]      FIG. 2  is a schematic perspective view of the scanning apparatus, showing both the laser and X-ray CT scanners made in accordance with the present invention.  
         [0015]      FIG. 3  is a schematic perspective view of the main components of an X-ray CT scanner shown in  FIG. 2 .  
         [0016]      FIG. 4  is a top view of  FIG. 3 , showing the breast within the X-ray scanner scanning field.  
         [0017]      FIG. 5  is a schematic perspective view of the main components of a laser CT scanner shown in  FIG. 2 .  
         [0018]      FIG. 6  is a top view of  FIG. 5 , showing the breast within the ring of detectors of the laser CT scanner.  
         [0019]      FIG. 7  is a top view of both the laser and x-ray CT scanners in relation to the breast.  
         [0020]      FIG. 8  is a block diagram of a process representing the main components in the image reconstruction from data collected by the x-ray CT scanner.  
         [0021]      FIG. 9  is a block diagram of a process representing the main components in the image reconstruction from data collected by the laser CT scanner.  
         [0022]      FIG. 10  is a continuous wave spectrophotometry of various materials. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0023]     A scanning apparatus made in accordance with the present invention comprises two independent CT scanners sharing a patient couch. The patient lies on the couch in a prone position, with one of the breasts vertically pendent through an opening in the couch for scanning. The two scanners share a common patient couch to facilitate a direct correlation of the reconstructed images representing the functional and anatomical structures of the breast that are derived from the data collected by the two scanners respectively. The laser scan of the breast is followed immediately by an x-ray scan or vice-versa in order to keep the patient position invariant. To advantageously shorten the total scan time, the two scans may be performed concurrently. Two independent image reconstruction systems are provided. The first is for the reconstruction of functional images from data collected by the laser CT scanner, and the other for the reconstruction of anatomical images from data collected by the x-ray CT scanner. To allow a physician to detect, locate and discern cancer cells inside the breast, the reconstructed images are displayed in 2D and 3D format. The images may be displayed separately or concurrently using image fusion based on the physical location of the cross-sections of the breast along which both sets of images were reconstructed. The fused images enable the visualization of the sets of images separately or concurrently in order to facilitate detection of cancer, its location and extent inside the breast.  
         [0024]     Referring to  FIG. 1 , an apparatus  2  made in accordance with the present invention is disclosed. The apparatus  2  includes a laser CT scanner  4  and an X-ray scanner  6 . The laser and X-ray CT scanners  4  and  6  are disposed below a patient couch  8 . The patient lies on the couch  8  in a prone position, having her breast  10  vertically pendent through an opening  12  in the couch  8 . The couch  8  is shielded according to standard methods to ensure that only the scanned breast is exposed to the x-ray radiation during the scan in order to minimize the radiation dose to the patient.  
         [0025]     The laser CT scanner  4  includes a laser source  14  and a ring of multiple rows of detectors  16  (also see  FIG. 2 ). The laser source  14  is mounted to a fixture (not shown), as will be explained below, that allows a helical movement of the laser source  14  during a scan. The ring of detectors  16  is mounted to the same fixture (not shown), as will be explained below, that allows a linear, up and down motion, during the scan. The movements of the laser source  14  and the detector ring  16  are synchronized in such a way that the laser source remains in a middle plane defined by a middle row of detectors in the detector ring. These movements are monitored by a laser scan controller  20 .  
         [0026]     The laser CT scanner  4  provides the collection of data for reconstruction of functional images of the breast. In medical imaging, functional images show the body at work. Examples of functional images are those showing blood flow, brain activities, oxygen consumption, oxy-hemoglobin increase, or what a tumor is doing to a body. In the case of laser tomography for breast cancer detection, an objective is to image pools of blood feeding cancer cells in the breast. This is done using the fact that blood absorbs more photons from the laser source than regular breast tissue does, causing less photons received at the detectors surrounding the breast.  
         [0027]     The x-ray CT scanner  6  includes an x-ray source  22  and an arc of multiple rows of detectors  24 . Both the x-ray source  22  and the detector arc  24  are mounted to a fixture  26  (see  FIG. 2 ), allowing a helical movement during a scan of the breast. This movement is monitored by an X-ray scan controller  28 .  
         [0028]     Functional data are collected by a laser data acquisition system  30  during an optical scan when the laser source  14  emits a pencil beam continuously toward the breast. To determine the boundary of the breast, a portion of the light reflected from the incidence of the laser beam with the breast is recorded by two CCD cameras mounted near the laser source, as described in U.S. Pat. No. 6,044,288. For the sake of clarity, the cameras are not shown. This data set is also collected by the laser data acquisition system  30 . These two sets of data are then fed to a laser CT reconstruction system  32 , which is responsible for generating functional images along a plurality of cross sections of the breast, as described in U.S. Pat. No. 6,130,958. The reconstructed functional images are in a format readily available to be displayed by a visualization system  34 . The laser CT scan controller  20  supervises the laser data acquisition system  30 .  
         [0029]     Anatomical data are collected by an X-ray data acquisition system  36  during an X-ray CT scan when the X-ray source  22  emits a limited cone beam toward the breast. This data set is fed to an x-ray CT reconstruction system  38 , which is responsible for generating anatomical images along a plurality of cross sections of the breast. The reconstructed anatomical images are in a format readily available to be displayed by the visualization system  34 . The x-ray CT scan controller  28  supervises the x-ray data acquisition system  36 .  
         [0030]     The visualization system  34  is responsible for displaying functional and anatomical images in various formats, including cross-section, sagittal, coronal, or 3D views. The 3D views may be in the form of surface shading, maximum intensity projection (MIP) or volume rendering (VR). The functional anatomical images may be displayed separately or concurrently using an image fusion process based on the exact physical location of the cross-sections of the breast along which both sets of images were reconstructed.  
         [0031]     The X-ray CT scanner  6  produces images showing anatomical structure of the breast including, for example, fat, soft tissue, blood vessels, etc. If there are tumors, the tumors are shown in the CT images. However, both benign and malignant tumors are shown the same way so that it is very difficult, if not impossible, to distinguish them by viewing CT images. Functionally, malignant tumors require blood for their growth. The blood concentration feeding the tumors can be picked up by the laser CT scanner  4  and shown in the laser CT images, but not the tumors themselves. A way to correlate the tumors with their blood supply is through their relative locations within the images from the two modalities.  
         [0032]     X-ray CT images (anatomical images) and laser CT images (functional images) of the breast constitute two sets of slices reconstructed from the data collected by the corresponding scanners. In both cases, the slice locations are known from the reconstruction process and the data collection. From this knowledge, the slices from these 2 sets of images are correlated. Image slice interpolations within one set of images may be required if the images of the 2 sets were not reconstructed at the same slice locations.  
         [0033]     Consequently, it is advantageous to combine two images from the 2 sets at the same slice location, creating another image showing the characteristics of both original images at the same time. A linear combination of the grey level (image intensity) of the two images at the same pixel location is commonly used in this process. The resulting image will show the tumors from the x-ray CT image and the blood concentration from the laser CT image within the same area if the tumors are malignant.  
         [0034]     Final images prepared by the visualization  34  are displayed on a single or multiple display monitors  40  via a display controller  42 .  
         [0035]     An operator controls or selects a mode of operation of the apparatus  2  via a scan user interface system  44 , which extracts relevant parameters from the user input and passes them on to a system controller  46 . Using these parameters, the system controller  46  controls and monitors the operations of the scanner by issuing appropriate commands to either the laser CT controller  20  or X-ray CT controller  28 . The status of the scanner is fed back from both the laser and x-ray CT controllers to the system controller. Some of the status may be fed back to the operator via the scan user interface system  44 .  
         [0036]     Referring to  FIG. 2 , a schematic perspective view of the apparatus  2  is disclosed, showing a patient lying in a prone position on the couch  8 . Underneath the couch are the laser and X-ray CT scanners  4  and  6 .  
         [0037]     The X-ray source  22  and the arc of detectors  24  are attached to a mechanical structure  47  comprising a rotor  48  of a bearing  50 . The arc of detectors  24  and the X-ray source  22  are attached to the rotor  48 , enabling a circular motion for scanning. A stator  52  of the bearing is supported by four vertical actuators  54 , which facilitate a linear, up and down motion  56  during the scan. The rotation  57  of the rotor  48  and the linear, up and down motion  56  of the stator  52  provide a helical movement of the x-ray source  22  and the detectors  24  for scanning purpose.  
         [0038]     A mechanical structure similar to the structure  47  comprising a bearing and linear up and down actuators, but smaller in size is provided to support the laser source  14  and detector ring  16 , enabling a helical motion of the laser source and the detector ring  16  for scanning. For the sake of clarity, this mechanical structure is not shown in the figure.  
         [0039]     The helical movements supported by the two above mechanical fixtures are preferably decoupled in order to provide independent scans by the laser and X-ray CT scanners.  
         [0040]      FIG. 3  shows the extent of a limited cone beam  57  of X-ray radiation required for scanning. The limited cone beam  57  is realized by placing a collimator, not shown in the figure, located near the X-ray tube  22 , right in front of the X-ray focal spot. At one particular instance of time during a scan, an area  58  of the breast  10 , is exposed to the radiation dose, depending on the location of the x-ray tube  22  and that of the arc of detectors  24 . The arc of detectors comprises multiple rows of individual detectors  59 . The limited cone beam  57  is further disclosed in co-pending application Ser. No. 11/494,534, filed Jul. 29, 2006, herein incorporated by reference. As discussed in the cited co-pending application, a limited cone beam is advantageously used to reduce the radiation dose to the patient.  
         [0041]      FIG. 4  is a schematic top view of  FIG. 3 , showing the extent of the limited cone beam  57 . The x-ray tube  22  and the detector area  24  are positioned so that any cross-section of the breast  10  would be within a region  60  within the boundary of the cone beam  57 .  
         [0042]      FIG. 5  shows the ring of detectors  16  made up of multiple rows of individual detectors  61  for laser scanning with the laser source  14 . During a scan, the laser source  14  emits a pencil beam  62  of laser toward the breast  10 . Upon hitting the breast, photons of the laser beam scatter in all directions. Some are absorbed inside the breast and some survive and exit the breast. Some of the surviving photons are detected by the detectors  61  of the ring, giving rise to the so called “optical data” used for image reconstruction.  
         [0043]     The detectors  61  may be provided with optical filters to allow detection of photons only within a selected predefined narrow range of wave lengths. Optical filters are commonly used to detect fluorescent emission from the far-brighter excitation light of the laser source. These filters are usually interference filters, composed of many layers of optical material deposited on glass. The filters may be either bandpass or longpass filters and are disposed close to the optical detectors  61 .  
         [0044]      FIG. 6  is a schematic top view of the of  FIG. 5  that shows the relative positions of the detectors  61  within the top row of detectors of the ring  16 , as well as the relative positions of the detector ring  16  and the laser source  14  with respect to the position of the breast  10 . Note that the laser source  14  is disposed within the detector ring  16 . The ring of detectors  16  moves up and down vertically, while the laser source  14  rotates around the breast  10  to provide a helical path during scanning.  
         [0045]      FIG. 7  provides a top view of the x-ray CT scanner  6  and laser CT scanner  4 , showing the relative positions of the x-ray source  22 , detector arc  24 , laser source  14 , detector ring  16  with respect to the position of the breast  10 . Note that the laser detector ring  16  and the laser source  14  are disposed between the X-ray source  22  and the arc of detectors  24 .  
         [0046]     During a scan using x-ray CT scanner  6 , the x-ray data acquisition system  36  collects a set of data representing information pertaining to the x-ray attenuation through the breast. In order to render this information easily readable, this data set is submitted to an image reconstruction process  66  shown in  FIG. 8 . The image reconstruction is done for the whole scanned volume of the breast. The scanned volume is embedded in a parallelepiped, which is subdivided into small volume elements known as voxels. The value of the reconstructed images at each voxel is the result of a 3D back-projection  88 , as disclosed in Feldkamp et al., J. Opt. Soc. Am. A1, 612-619, 1984, incorporated herein by reference, or summation of data values along rays going through the 3D location of the voxel and the x-ray source locations when the source encircles the voxel in a period of π, along the helix. The data values contributing in the image reconstruction at each voxel are derived from the data collected by the X-ray data acquisition system  36 . In order to ensure proper values of reconstructed images, the following data processing steps are applied to the collected data set before the 3D back-projection  68  takes place. 
        a) Data correction process  70  to correct for errors and inconsistencies introduced by various physical components utilized for the data acquisition. The source of errors and inconsistencies may include the mA variations of the high voltage generator to the x-ray source, the beam walk caused by non stable focal spot, non-linear and non-uniform response of detectors, non-perfect geometric locations to the x-ray sources or detectors.     b) Rebinning process  72  to derive from the above corrected data set another data set according to a different geometry underlying a fictive theoretical data collection. The choice of the new geometry is simply to facilitate a correct but simple 3D back-projection process  68 . Parallel beam geometry is a preferred geometry for the present embodiment of the invention.     c) Convolution process  74  to ensure a sharp or less blurred resultant back-projected image. The convolution kernel may be a 2D or 1D filter derived from the ramp filter, as disclosed in Ramachandran et al., Proc. Nat. Acad. Sci. U.S., 68, 2236-2240, 1971, incorporated herein by reference. A 1D ramp filter is a preferred filter for the present invention.        
 
         [0050]     The process  66  provides a preferred sequence of data processing starting from the raw data collected by the x-ray data acquisition system  36  to reconstructed images feeding to the visualization system  34 .  
         [0051]     During a scan using the laser CT scanner  4 , the laser data acquisition system  30  collects an optical data set representing information resulting from the scatter and absorption phenomena of the photons from the laser source  14  as they travel through the breast  10 . In order to render this information easily readable, the optical data set is submitted to an image reconstruction process  76  shown in  FIG. 9 . Similar to the above reconstruction process  66  described for the x-ray system, the image reconstruction is done for whole scanned volume of the breast. The scanned volume is embedded in a parallelepiped, which is subdivided into small volume elements known as voxels. The value of the reconstructed images at each voxel results from an optical 3D back-projection  78  or simply a summation of data values along maximum probable photon paths, as disclosed in S. Feng et al., SPIE, 1888, 78-89, 1993, incorporated herein by reference, going through the 3D location of the voxel and the laser source locations as the source encircles the voxel in a period of 2π, along the helix. The data values contributing in the image reconstruction at each voxel are derived from the data collected by the laser data acquisition system  30 . In order to ensure proper values of reconstructed images, the following data processing steps are applied to the collected data set before the 3D optical back-projection  78  takes place. 
        a) Data correction process  80  to correct for errors and inconsistencies introduced by various physical components utilized for the data acquisition. The source of errors and inconsistencies may include the power variations of the laser source, non-linear and non-uniform response of detectors, non-perfect geometric locations to the laser sources or detectors.     b) Background removal  82  to reveal the signal caused by inclusions inside the breast from the corrected data set. This background removal makes use of the data representing the boundary of the breast in order to estimate optical signal that would have had been detected if the laser source would have shined on a homogeneous media of the same dimensions as that of the breast. Background removal is a procedure of taking the log of the ratio between the optical measurements derived from the measurements from the scanner during the scan of the breast, and an estimation of uniform background derived from an estimation of solution of the homogeneous diffusion equation satisfying the boundary condition derived from the boundary of the breast, which was recorded during the scan.     c) Rebinning process  84  to derive from the above estimated perturbation signal, another data set according to a different geometry underlying a fictive theoretical data collection. The choice of the new geometry is simply to facilitate a correct but simple 3D optical back-projection process  78 . Parallel beam geometry is a preferred geometry for the present invention.     d) Convolution process  86  to ensure a sharp or less blurred resultant back-projected image. The convolution kernel may be a 2D or 1D filter derived from the ramp filter, as disclosed in Ramachandran et al., Proc. Nat. Acad. Sci. U.S., 68, 2236-2240, 1971. A 1D ramp filter is a preferred filter in the present embodiment of the invention.        
 
         [0056]     The process  76  provides a preferred sequence of data processing starting from the raw data collected by the laser data acquisition system  30  to reconstructed images feeding to the visualization system  34 .  
         [0057]     A scan generates a geometry, called scan geometry, described by the locations of the source (x-ray or laser), and the locations of all the detectors of the scanner when the signals are recorded and collected. The scan geometry is to indicate that data are known along the rays joining the source and detectors at the time that the data are recorded. For each instance of data collection—the rays along which data are recorded—are within a cone or a fan with the source position being its vertex. From this point of view the scan geometry consists of a set of fans or limited cone beams.  
         [0058]     On the other hand, image reconstruction is done via a back-projection process, more precisely, the value of the reconstructed image at a voxel is the back-projection of convolved data at that voxel. As disclosed in co-pending application Ser. No. 11/494,534, filed Jul. 29, 2006, herein incorporated by reference, for the back-projection, it is advantageous to assume that data are known in a “curly wedge beam” geometry, which is different than the scan geometry. For this reason, it is required to synthesize data in the curly wedge beam geometry from data in the scan geometry before the convolution takes place. This process is known as the rebinning process.  
         [0059]     The rebinning is done on a ray by ray basis. For a given ray in the wedge beam geometry, we look for 4 closest rays in the scan geometry. The data along that particular given ray is estimated by computing an interpolation of the collected data along these 4 closest rays. The coefficients of the interpolation is inferred from the relative location of the given ray with respect to its 4 closest rays, similar to what was disclosed in the co-pending application Ser. No. 11/494,534.  
         [0060]     The scatter and absorption of photons during their travel through various tissues of the breast depend on the tissues and the wave length of the laser. It is advantageous for the user to be able to select the wave length of the laser in order to emphasize or deemphasize the structure he wants to view. A selection of a proper wave length may be based on the absorption factor curve as a function of materials and wave length.  FIG. 10  shows an example of such curves (see V. Tuchin, Tissue Optics, SPIE Press, vol. TT38, 156-157, 2000). Based on these curves, the wave length in a neighborhood of 805 nm, which corresponds to an oxy-deoxyhemoglobin isosbestic point, is selected if both oxyhemoglobin and deoxyhemoglobin concentration areas are of the same informational value to the user. On the other hand, if the deoxyhemoglobin area is more important to view than the oxyhemoglobin area, then a wave length in a neighborhood of 760 nm would be selected.  
         [0061]     The laser wavelength illuminating the patient may be selected electronically or mechanically, as is well known in the art. The outputs of multiple lasers could be optically combined, either via a fiber-optic combiner or via a series of dichroic mirrors, both techniques being well known in the optics industry. Then the lasers would be pulsed on sequentially via their respective controllers, giving a time-sequenced wavelength selection.  
         [0000]     Alternatively, the lasers could be mechanically selected, via either a fiber-optic switch or via a galvanometer-controlled moving mirror, both being well known in the optics field.  
         [0062]     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.