Patent Publication Number: US-2023143179-A1

Title: 3D Particle Analysis and Separation Using Dual Seeding

Description:
RELATED APPLICATIONS 
     This application claims the benefit under 35 USC 119(e) of U.S. Provisional Application No. 63/263,628, filed on Nov. 5, 2021, which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     Various imaging modalities have been used to identify and visualize mineral content of rocks, both in two dimensions (2D) and in three dimensions (3D). For example, these imaging modalities can analyze rock samples from extraction operations to determine porosity and mineralogy for exploration and production operations in the Oil and Gas industry, or determine comminution statistics for the mining industry. 
     In typical operation, these imaging modalities create image datasets such as 3D volumes or 2D images. Image analysis techniques are then employed to infer grain characteristics and mineral content from the volumes and the images. 
     Non-destructive imaging systems include x-ray computed tomography (CT) microscopy and Scanning Electron Microscopy (SEM) systems. These systems provide the ability to visualize features such as pores, organics and minerals in the samples. 
     The X-ray CT microscopy systems irradiate the sample with x-rays, typically in a range between 1 and several hundred keV. 2D projection images are collected at multiple angles and a 3D volume of the sample is reconstructed from the projections. 
     One current imaging analysis technique creates a 3D mineral map of the sample by analyzing volume image datasets of a sample created from x-ray imaging systems. A total mineral content of the sample is then defined, and x-ray attenuation coefficients are calculated for the defined minerals. The technique then segments the grey scale 3D images by identifying characteristic grey scale levels in the images corresponding to the calculated x-ray attenuation coefficients. 
     Another imaging analysis technique employs multi-phase segmentation of 3D x-ray tomography volume image datasets. The 3D x-ray tomography volumes are processed to obtain standardized intensity grey scale images, which are then segmented into at least 3 phases. The segmentation steps include computing a median/mean-filtered-gradient image of the standardized intensity image, creating an intensity vs. gradient graph from the median/mean-filtered-gradient image and the standardized intensity image, partitioning the intensity vs. gradient graph into at least 3 regions, and using thresholds defining the regions to segment the standardized grey scale image to create the segmented image. Then, volumetric fractions and spatial distributions of the segmented phases are calculated and compared with target values. 
     SUMMARY OF THE INVENTION 
     Segmentation is also a challenge when analyzing samples with small grains or even powders when a range of particle sizes are present in the sample. Therefore, multiscale segmentation approaches are required in this domain. 
     In general, according to one aspect, the invention features a sample segmentation method. This method comprises generating one or more volume datasets of a sample, binarizing the dataset into areas classified as background and particles to create a binary image, generating a distance transform image from the binary image, creating markers to identify unique particles, for at least two particle size classifications within the sample independently, and dilating the markers to merge into particles. 
     Preferably, the markers for the different particle sizes are processed differently. 
     A composite image can be created by overlying an image for smaller particles and an image for larger particles. 
     With respect to large particles, the distance image can be thresholded and any small objects can be removed to create the large markers. Then, for the small particles, the distance transform image is run through an H-max algorithm. 
     In the preferred embodiment, a user can change threshold values and measurements and statistics are calculated for the particles, such as minor and major axis length, total volume, surface area, sphericity, and association measurements. 
     In general, according to one aspect, the invention features an x-ray microscopy CT system, comprising: a source of generating x-rays, a sample holder for holding and rotating samples in the beam, and a detector for detecting the beam after interaction with the samples. The system further has a computer for receiving projections from the detector and generating one or more volume datasets of samples, and segmenting slices of the volume datasets by binarizing the dataset into areas classified as background and particles to create a binary image, generating a distance transform image from the binary image, creating markers to identify unique particles, for at least two particle size classifications within the sample independently, and dilating the markers to merge into particles. 
     The above and other features of the invention including various novel details of construction and combinations of parts, and other advantages, will now be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the particular method and device embodying the invention are shown by way of illustration and not as a limitation of the invention. The principles and features of this invention may be employed in various and numerous embodiments without departing from the scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the accompanying drawings, reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale; emphasis has instead been placed upon illustrating the principles of the invention. Of the drawings: 
         FIG.  1    is a schematic diagram of an x-ray CT system to which the present invention is applicable; 
         FIG.  2    is a flow diagram showing a process for segmentation executed by a computer system; 
         FIG.  3    is a slice of a 3D mineral dataset as displayed on a display device of the computer system; 
         FIG.  4    is the slice of a 3D mineral dataset depicted in  FIG.  3    after having undergone particle separation as displayed on the display device of the computer system. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The invention now will be described more fully hereinafter with reference to the accompanying drawings, in which illustrative embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. 
     As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. Further, the singular forms and the articles “a”, “an” and “the” are intended to include the plural forms as well, unless expressly stated otherwise. It will be further understood that the terms: includes, comprises, including and/or comprising, when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. Further, it will be understood that when an element, including component or subsystem, is referred to and/or shown as being connected or coupled to another element, it can be directly connected or coupled to the other element or intervening elements may be present. 
       FIG.  1    is a schematic diagram of an x-ray CT system  100  on which the present invention can be implemented. 
     In general, the x-ray CT system  100  includes an x-ray source system  102  that generates an often polychromatic x-ray beam  104  and a rotation and positioning stage  110  with sample holder  112  for holding the sample  114  in the x-ray beam  104  from the x-ray source system  102 . Images or x-ray projections are captured by a detector system  118 . The x-ray source system  102 , the rotation and positioning stage  110 , and the detector system are mounted to a base  108  of the x-ray CT system  100 . A computer system  200  typically receives and processes these images or projections and provides general control of the system  100 . The computer system  200  possibly along with a special purpose graphics processor will typically perform tomographic reconstruction using the x-ray projections. 
     The x-ray source  102 , in one example, is a polychromatic x-ray source. Laboratory x-ray sources are often used because of their ubiquity and relatively low cost. Nonetheless, synchrotron sources or accelerator-based sources are other alternatives. 
     Common laboratory x-ray sources include an x-ray tube, in which electrons are accelerated in a vacuum by an electric field and shot into a target piece of metal, with x-rays being emitted as the electrons decelerate in the metal. Typically, such sources produce a continuous spectrum of background x-rays (i.e. bremsstrahlung radiation) combined with sharp peaks in intensity at certain energies that derive from the characteristic lines of the target, depending on the type of metal target used. 
     In one example, the x-ray source  102  is a rotating anode type or micro focused source, with a Tungsten target. Targets that include Molybdenum, Gold, Platinum, Silver or Copper also can be employed. A transmissive configuration of the x-ray source  102  can be used in which the electron beam strikes the thin target  103  from its backside. The x-rays emitted from the other side of the target  103  are then used as the beam  104 . Reflection targets are another option. 
     The x-ray beam  104  generated by source  102  has an energy spectrum that is controlled typically by the operating parameters of the source. In the case of a laboratory source, important parameters include the material of the target and the acceleration voltage (kVp). The energy spectrum is also dictated by any conditioning filters that suppress unwanted energies or wavelengths of radiation. For example, undesired wavelengths present in the beam can be eliminated or attenuated using, for instance, an energy filter (designed to select a desired x-ray wavelength range /bandwidth). 
     In addition to the x-ray source  102 , filters are sometimes useful for filtering the x-ray beam  104  before interaction with the sample  114  (pre-filters). 
     When the sample  114  is exposed to the x-ray beam  104 , the x-ray photons transmitted through the sample form an attenuated x-ray beam  106  that is received by the spatially resolved detector system  118 . 
     In the most common configuration of the detector system  118 , a magnified projection image of the sample  114  is formed on the detector system  118  with a geometrical magnification that is equal to the inverse ratio of the source-to-sample distance and the source-to-detector distance. Generally, the geometrical magnification provided by the x-ray stage is between 2 x and 100 x, or more. In this case, the resolution of the x-ray image is limited by the focus spot size or virtual size of the x-ray source system  102 . 
     To achieve high resolution, an embodiment of the x-ray CT system  100  further utilizes a very high resolution detector  124 - 1  of the detector system  118  in conjunction with positioning the sample  114  close to the x-ray source system  102 . In one implementation of the high-resolution detector  124 - 1 , a scintillator is used in conjunction with a microscope objective to provide additional magnification in a range between 2 x and 100 x, or more. 
     Other possible detectors can be included as part of the detector system  118  in the illustrated x-ray CT system  100 . For example, the detector system  118  can include a lower resolution detector  124 - 2 , as shown in the illustrated embodiment of  FIG.  1   . This could be a flat panel detector or a detector with a lower magnification microscope objective, in examples. Configurations of one, two, or even more detectors  124  of the detector system  118  are possible. 
     Preferably, two or more detectors  124 - 1 ,  124 - 2  are mounted on a turret  122  of the detector system  118 , so that they can be alternately rotated into the path of the attenuated beam  106  from the sample  114 . 
     Typically, based on operator defined parameters, the controller  210  of the computer system  200  instructs the rotation stage  110  via the control interface  130  to move the sample  114  out of the beam path during x-ray source system  102  calibration. After completion of the calibration portion, the controller  210  moves the sample  114  back into the beam path and rotates the sample  114  relative to the beam  104  to perform the CT scan of the sample  114 . 
     In one example, the computer system  200  includes an image processor  202  that accelerates the analysis of the x-ray projections and possibly performs the calculations necessary for tomographic reconstructions created from the x-ray projections. A display device  240 , connected to the computer system  200 , displays information from the x-ray CT system  100 . An input device  250  such as a touch screen, keyboard, and/or computer mouse enables interaction between the operator, the computer system  200 , and the display device  240 . 
     A user interface application  208  executes on an operation system  206  that controls access to a central processing unit CPU  205  of the computer system  200 . In one example, the operator defines/selects CT scan or calibration parameters via the user interface  208 . These include x-ray acceleration voltage settings, and settings for defining the x-ray energy spectrum of the scan and exposure time on the x-ray source system  102 . The operator also typically selects other settings such as the number of x-ray projection images to create for the sample  114 , and the angles to rotate the rotation stage  110  for rotating the sample  114  for an x-ray CT scan in the x-ray beam  104 , along with the positioning of the sample in the beam along the x, y, and z axes. 
     The computer system  200 , with the assistance of its image processor  202 , accepts the image or projection information from the detector system  118  associated with each rotation angle of the sample  114 . The image processor  220  creates a separate projection image for each rotation angle of the sample  114 , and combines the projection images using CT reconstruction algorithms  209  to create 3D tomographic reconstructed volume information for the sample. 
     In addition, a segmentation application  207  also runs on the operating system  206  and the CPU  205 . This is used to segment the different features, such as particles, within the sample, which is often in the form of a powder, and to identify and otherwise analyze those particles to automatically generate comminution statistics, for example. 
       FIG.  2    shows a process for segmentation employed by the segmentation application  207 . 
     The first step is to segment or binarize the dataset into areas classified as background and particles in step  312 . 
     Then the distance transform image is produced from this binary image in step  314 . An appropriate Euclidian distance transform is described in Strutz, The Distance Transform and its Computation June, 2021, TECHP/2021/06, arXiv:2106.03503v1. 
     From there, markers are created and used to identify unique particles, for small and large particles independently in step  316 . The following articles describe appropriate possible implementations: Rabbani, A., Jamshidi, S. &amp; Salehi, S. An automated simple algorithm for realistic pore network extraction from micro-tomography images. J. Pet. Sci. Eng. 123, 469 164-171 (2014); Andrew, M. G., Menke, H. P., Blunt, M. J. &amp; Bijeljic, B. The Imaging of Dynamic Multiphase Fluid Flow Using Synchrotron-Based X-ray Microtomography at Reservoir Conditions. Transp. Porous Media 110, 1-24 (2015); Wildenschild, D. &amp; Sheppard, A. P. X-ray imaging and analysis techniques for quantifying pore-scale structure and processes in subsurface porous medium systems. Adv. Water Resour. 51, 217-246 (2013), Beucher, S. &amp; Lanteujoul, C. Use of watersheds in Contour Detection. in International workshop on image processing: real-time edge and motion detection/estimation (1979). See also U.S. Pat. Appl. No. US 20210182597 A1 by Matthew Andrew, which is incorporated herein by this reference. 
     For the large particles, the distance transform image is thresholded and any small objects are removed to create the large markers in step  318  to produce a thresholded distance image. 
     For the small particles, the distance transform image is run through the H-max algorithm in step  320 . Soille, P., “Morphological Image Analysis: Principles and Applications” (Chapter 6), 2nd edition (2003), ISBN 3540429883 describes an appropriate approach for generating the H-max image. 
     Then these two sets of images, the thresholded distance image and the H-max image, are overlayed in step  324 . This yields a composite marker image that covers both large and small particles. 
     The markers are then dilated to merge any that are not touching each other but are indicating the same particle in step  326 . This helps address any over separation that might occur. 
     Finally the independent markers are labeled and the distance transform image is flooded using this labelled marker image in step  328 . 
     The output of that is a label dataset where each particle is assigned a unique value as shown in  FIG.  4   , when starting from a slice from a 3D mineral dataset as shown in  FIG.  3   . 
     To allow for flexibility, the segmentation application allows the user to change a few of the parameters like the threshold value applied to the distance transform image to optimize the final label image. 
     After the dataset has gone through particle separation, the method then begins recording and calculating a number of relevant measurements and statistics. This is done for both the particles as well as grains. Some of the outputted 3D measurements include minor and major axis length, total volume, surface area, sphericity, etc. as well as association measurements as to what phase certain grains are in contact with. 
     While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.