摘要:
A method and apparatus for detecting objects in computed tomography (CT) data are disclosed. Erosion of the data can be performed by identifying a neighborhood of voxels surrounding a voxel of interest. If the number of voxels having densities below a predetermined threshold exceeds a predetermined number, then it is assumed that the voxel of interest is a surface voxel of an object and is removed from the object. A connectivity process is then applied to remaining voxels to combine them into objects. A dilation function can then be performed on the eroded object to replace surface voxels removed by erosion. This morphological connected components labeling (CCL) approach separates adjacent objects in the data such that they can be individually labeled and analyzed.
摘要:
A method and apparatus for detecting objects in computed tomography (CT) data are disclosed. Sheet-shaped objects such as sheet explosives can be detected by analyzing a neighborhood of voxels surrounding a test voxel. If the density of the test voxel is sufficiently different from the mean density of the neighboring voxels, then it is concluded that the test voxel is associated with a sheet object. Sheet objects can also be detected by eroding the CT data so as to eliminate voxels associated with thin objects. Remaining objects are then subtracted from the original data, leaving only thin sheet-shaped objects. Bulk objects can be detected by a modified morphological connected components labeling (CCL) approach which performs a series of erosion and dilation steps to separate adjacent objects in the data such that they can be individually labeled and analyzed. The process of the invention can be carried out in multiple paths. That is, for example, a sheet object detection process and a bulk object detection process can be implemented separately and in parallel. During the sheet object detection process, the data can be analyzed to identify bulk objects. Those objects can then be removed from the data and the remaining data can then be analyzed to identify any remaining sheets. Redundant analysis of data is eliminated.
摘要:
Sheet-shaped objects can be detected by analyzing voxels surrounding a test voxel. If the density different from the mean density then the test voxel is associated with a sheet object. Sheet objects can also be detected by eroding the CT data. Remaining objects are then subtracted from the original data removing with surface voxels, being removed. A connectivity process combines voxels into objects after sheets are detected A dilation function replaces surface voxels removed by erosion. A corrected mass can be compared to mass thresholds to classify the object. Multiple mass thresholds can be used, each of which is associated with a particular density range based on the density of an expected threat object. Bulk objects can be detected by a modified morphological connected components labeling (CCL) approach. A merging process can be used to reconnect related items, The system can also identify objects that contain liquids. The overall system performance, including overall object detection rate and false alarm rate, can be adjusted by adjusting individual object detection rates and/or false alarm rates.
摘要:
A method of and system for detecting threat objects represented in 3D CT data uses knowledge of one or more predefined shapes of the threat objects. An object represented by CT data for a region is identified. A two-dimensional projection of the object along a principal axis of the object is generated. A contour of the object boundary in the projection image is computed. A shape histogram is computed from the extracted contour. A difference measure between the extracted shape histogram and a set of pre-computed threat shape histograms is computed. A declaration of a threat object is made if the difference measure is less than a pre-defined threshold.
摘要:
A method of and apparatus for assessing the image quality of a CT scanner is described in which assessment can be made manually or automatically. No special image quality mode of CT scanner operation is necessary, and no precise alignment of the phantom is necessary. In general, performance of the scanner comprises: using the scanner (a) to scan a phantom in one or more of its normal modes of operation while translating said phantom along the scanner axis of rotation and (b) to produce scanned data of the phantom, and assessing the performance of the scanner from the scanned data. In accordance with another aspect, the assessment is performed by (a) using the scanner to scan a phantom in one or more of its normal modes of operation; (b) reconstructing a three-dimensional volume CT image for a region containing at least a portion of the phantom; (c) calculating properties of the CT image; and (d) using the calculated properties of the CT image to assess CT scanner performance.
摘要:
A method of and apparatus for detecting objects in computed tomography (CT) data includes the ability to define the types of objects to be detected, and at least one algorithm related to the detection of each type of object. Multiple types of objects can be detected and distinguished from one another. Each type of object exhibits an object detection rate related to the probability of the system detecting the corresponding object type, and a false detection rate related to the false identification of objects, different from the target objects, as the target objects. An overall system detection rate is related to a combination of the object detection rates. Each type of object can also be associated with a unique object false alarm rate, with a overall false detection rate being related to the combination of object false alarm rates. The overall system and/or object detection rate, and/or the false alarm rate and/or the overall false detection rate can be optimized by modifying at least one algorithm so as to adjust at least one of the object detection rates or object false alarm rate.
摘要:
A method and apparatus for detecting concealed objects in computed tomography data are disclosed. Sheet-shaped objects such as sheet explosives can be detected by a CT scanning system, in particular, a CT baggage scanning system. The invention analyzes CT voxels in a subregion in proximity to the sheet object to determine if the sheet object is concealed in an electronic device or is “sandwiched” within an item such as a book or magazine. To detect electronic concealment, the number of voxels in a subregion that contains the object having a density above a predetermined threshold is counted and the ratio of that number of voxels to the number of object voxels is computed. If the ratio exceeds a threshold, then it is concluded that the object is concealed in electronics. In response, the CT scanning system can alter discrimination parameters to allow the object to be classified as a threat. For “sandwich” concealment, layers on opposite sides of a sheet object are examined. The mean and standard deviation of density values for the voxels are computed. Where the mean density exceeds a predetermined threshold and the standard deviation is below a different threshold, for at least one of the layers, then it is concluded that the sheet object is sandwiched within an innocuous object such as a magazine or a book.
摘要:
Sheet-shaped objects can be detected by analyzing a neighborhood of voxels surrounding a test voxel. If the density is sufficiently different, then the voxel is associated with a sheet object. Sheet objects can also be detected by eroding the CT data so as to eliminate voxels associated with thin objects. Remaining objects are then subtracted from the original data, leaving only thin sheet-shaped objects. If the number of voxels having densities below a predetermined threshold exceeds a predetermined number, then it is assumed that the test voxel is a surface voxel and is removed from the object. A connectivity process can be applied to voxels to combine them into objects after sheets are detected. A dilation function can then be performed to replace surface voxels. A corrected mass can be compared to mass thresholds. Bulk objects can be detected by a modified morphological connected components labeling (CCL) approach. A merging process can be used to reconnect related items. The system can also identify objects that contain liquids. The object detection rate and false alarm rate can be adjusted by adjusting individual object detection rates and/or false alarm rates.
摘要:
A method and apparatus for detecting and classifying objects in computed tomography (CT) data are disclosed. A connectivity process can be applied to voxels in the data to combine them into objects. A dilation function can then be performed on the eroded object to replace surface voxels removed by erosion. A corrected mass using the mean eroded density of the object can be computed and compared to mass thresholds to classify the object as to whether it poses a threat. Multiple mass thresholds can be used, each of which is associated with a particular density range based on the density of an expected threat object.
摘要:
A method and apparatus for detecting objects in computed tomography (CT) data are disclosed. Sheet-shaped objects such as sheet explosives can be detected by analyzing a neighborhood of voxels surrounding a test voxel. If the density of the test voxel is sufficiently different from the mean density of the neighboring voxels, then it is concluded that the test voxel is associated with a sheet object. Sheet objects can also be detected by eroding the CT data so as to eliminate voxels associated with thin objects. Remaining objects are then subtracted from the original data, leaving only thin sheet-shaped objects. Erosion of the data can be performed by identifying a neighborhood of voxels surrounding a voxel of interest. If the number of voxels having densities below a predetermined threshold exceeds a predetermined number, then it is assumed that the test voxel is a surface voxel and is removed from the object. A connectivity process can be applied to voxels to combine them into objects after sheets are detected to prevent sheets from being inadvertently removed from the data by erosion. A dilation function can then be performed on the eroded object to replace surface voxels removed by erosion. A corrected mass using the mean eroded density of the object can be computed and compared to mass thresholds to classify the object as to whether it poses a threat. Multiple mass thresholds can be used, each of which is associated with a particular density range based on the density of an expected threat object. Bulk objects can be detected by a modified morphological connected components labeling (CCL) approach which performs a series of erosion and dilation steps to separate adjacent objects in the data such that they can be individually labeled and analyzed. A merging process can be used to reconnect related items, such as multiple sticks, that were separated during an erosion step. The merging process allows multiple objects that would individually pass as non-threat items to be combined into a single item that is correctly classified as a threat. The system can also identify objects that contain liquids, if desired. The process of the invention can be carried out in multiple stages. The overall system performance, including overall object detection rate and false alarm rate, can be adjusted by adjusting individual object detection rates and/or false alarm rates.