Abstract:
Methods and apparatus for reconstructing a multiple resolution images of an object are provided. The method includes reconstructing a first three-dimensional image at a first resolution, determining at least one volume of interest in the generated image, and reconstructing a second three-dimensional image of the determined at least one volume of interest at a second resolution, the second resolution being higher than the first resolution such that a quantification of image structures is facilitated.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This invention generally relates to rotating imaging scanner systems and more particularly, to methods and systems for optimizing high resolution image reconstruction. 
         [0002]    Detecting an accurate shape and size of small objects in CT images for example, a volume of soft plaque in a coronary vessel is affected by the resolution of the images that are being analyzed. To achieve the most accurate estimation of small volumes, the images of the object should be viewed at the highest possible resolution. However, because of limitations of storage space and workflow, acquisition of images at the highest resolution available on a CT system may not be possible. 
         [0003]    Small airways in lungs are the early precursors of thoracic diseases for example, but not limited to chronic obstructive pulmonary disease (COPD), asthma, and bronchitis. Changes in the wall thickness and lumen of these small airways (&lt;2 mm) facilitate indicating the progression of the disease at the very onset. Current clinical image acquisition techniques for lungs do not provide enough resolution for an accurate measurement of these airways. High-resolution reconstruction can help the accuracy but current clinical protocols do not use these because of the high number of images required to cover an entire field of view at such a reconstruction resolution. In addition, for diagnostic readings, doctors, physicians, and radiologists require images covering the full field of view of the lungs. Moreover, some of the reconstruction parameters used clinically for diagnostic reading of lung images have been found to be not suitable for quantitative analysis. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0004]    In one embodiment, a method for reconstructing a multi-resolution image of an object includes reconstructing a first three-dimensional image at a first resolution, determining at least one volume of interest in the generated image, and reconstructing a second three-dimensional image of the determined at least one volume of interest at a second resolution, the second resolution being higher than the first resolution such that a quantification of image structures is facilitated. 
         [0005]    In another embodiment, an imaging system includes a stationary member, a rotating member rotatably coupled to the stationary member wherein the rotating member includes an opened area proximate an axis about which the rotating member rotates. The imaging system also includes an x-ray source provided on the rotating member, and an x-ray detector disposed on the rotating member and configured to receive x-rays from the x-ray source. The system further includes a processor communicatively coupled to at least one of the x-ray source and the x-ray detector wherein the processor is configure to receive image data relating to an object and then reconstruct a first image at a first resolution using the received image data, determine at least one volume of interest in the generated image, and reconstruct a second image of the determined at least one volume of interest at a second resolution, the second resolution being greater than the first resolution such that a quantification of image structures is facilitated. 
         [0006]    In yet another embodiment, a method of reconstructing a multi-resolution image of a patient includes receiving image data of at least one of a lung and a heart, reconstructing a first image at a first resolution from the received data, determining at least one volume of interest in the generated image, and reconstructing a second image of the determined at least one volume of interest at a second resolution, the second resolution being greater than the first resolution such that a quantification of image structures is facilitated. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a pictorial view of a computed tomography (CT) imaging system in accordance with an embodiment of the present invention; 
           [0008]      FIG. 2  is a block schematic diagram of the system illustrated in  FIG. 1 ; 
           [0009]      FIG. 3  is a flow chart of an exemplary method of improving segmentation, classification and quantification of small plaque deposits using an application driven optimum keyhole reconstruction technique in accordance with an embodiment of the present invention; and 
           [0010]      FIG. 4  is a flow chart of an exemplary method of enhancing accuracy of small airway measurements using adaptive interactive workflow-based optimum volume reconstruction in accordance with an embodiment of the present invention; and 
           [0011]      FIG. 5  is a screen shot of a multi-resolution image of a phantom generated using an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0012]    As used herein, an element or step recited in the singular and proceeded with the word “a” or “an” should be understood as not excluding plural said elements or steps, unless such exclusion is explicitly stated. Furthermore, references to “one embodiment” of the present invention are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. Moreover, unless explicitly stated to the contrary, embodiments “comprising” or “having” an element or a plurality of elements having a particular property may include additional such elements not having that property. For example, CT imaging apparatus embodiments may be described herein as having a plurality of detector rows that are used in a certain process. Such embodiments are not restricted from having other detector rows that are not used in that process. 
         [0013]    Also as used herein, the phrase “reconstructing an image” is not intended to exclude embodiments of the present invention in which data representing an image is generated but a viewable image is not. However, many embodiments generate (or are configured to generate) at least one viewable image. 
         [0014]    Referring to  FIGS. 1 and 2 , a multi-slice scanning imaging system, for example, a Computed Tomography (CT) imaging system  10 , is shown as including a gantry  12  representative of a “third generation” CT imaging system. Gantry  12  has an x-ray tube  14  (also called x-ray source  14  herein) that projects a beam of x-rays  16  toward a detector array  18  on the opposite side of gantry  12 . Detector array  18  is formed by a plurality of detector rows (not shown) including a plurality of detector elements  20  which together sense the projected x-rays that pass through an object, such as a medical patient  22  between array  18  and source  14 . Each detector element  20  produces an electrical signal that represents the intensity of an impinging x-ray beam and hence can be used to estimate the attenuation of the beam as it passes through object or patient  22 . During a scan to acquire x-ray projection data, gantry  12  and the components mounted therein rotate about a center of rotation  24 .  FIG. 2  shows only a single row of detector elements  20  (i.e., a detector row). However, multi-slice detector array  18  includes a plurality of parallel detector rows of detector elements  20  such that projection data corresponding to a plurality of quasi-parallel or parallel slices can be acquired simultaneously during a scan. 
         [0015]    Rotation of components on gantry  12  and the operation of x-ray source  14  are governed by a control mechanism  26  of CT system  10 . Control mechanism  26  includes an x-ray controller  28  that provides power and timing signals to x-ray source  14  and a gantry motor controller  30  that controls the rotational speed and position of components on gantry  12 . A data acquisition system (DAS)  32  in control mechanism  26  samples analog data from detector elements  20  and converts the data to digital signals for subsequent processing. An image reconstructor  34  receives sampled and digitized x-ray data from DAS  32  and performs high-speed image reconstruction. The reconstructed image is applied as an input to a computer  36 , which stores the image in a storage device  38 . Image reconstructor  34  can be specialized hardware or computer programs executing on computer  36 . 
         [0016]    Computer  36  also receives commands and scanning parameters from an operator via console  40  that has a keyboard. An associated cathode ray tube (CRT), liquid crystal (LCD), plasma, or another suitable display device  42  allows the operator to observe the reconstructed image and other data from computer  36 . The operator supplied commands and parameters are used by computer  36  to provide control signals and information to DAS  32 , x-ray controller  28 , and gantry motor controller  30 . In addition, computer  36  operates a table motor controller  44 , which controls a motorized table  46  to position patient  22  in gantry  12 . Particularly, table  46  moves portions of patient  22  through gantry opening  48 . 
         [0017]    In one embodiment, computer  36  includes a device  50 , for example, a floppy disk drive, CD-ROM drive, DVD drive, magnetic optical disk (MOD) device, or any other digital device including a network connecting device such as an Ethernet device for reading instructions and/or data from a computer-readable medium  52 , such as a floppy disk, a CD-ROM, a DVD or another digital source such as a network or the Internet, as well as yet to be developed digital means. In another embodiment, computer  36  executes instructions stored in firmware (not shown). Computer  36  is programmed to perform functions described herein, and as used herein, the term computer is not limited to just those integrated circuits referred to in the art as computers, but broadly refers to computers, processors, microcontrollers, microcomputers, programmable logic controllers, application specific integrated circuits, and other programmable circuits, and these terms are used interchangeably herein. 
         [0018]    It will be understood that the block diagram of  FIG. 2  is closer to a logical representation of the functions described herein than a physical block diagram. Particular hardware and/or firmware and/or software implementations of these functions can be left as a design choice to one or more people skilled in the art of logic and/or computational circuit design and/or computer programming upon such person(s) gaining an understanding of the principles of the present invention presented herein. 
         [0019]    Although the specific embodiment mentioned above refers to a third generation CT system, the methods described herein equally apply to fourth generation CT systems (stationary detector-rotating x-ray source) and fifth generation CT systems (stationary detector and x-ray source). Additionally, it is contemplated that the benefits of the invention accrue to imaging modalities other than CT. Additionally, although the herein described methods and apparatus are described in a medical setting, it is contemplated that the benefits of the invention accrue to non-medical imaging systems such as those systems typically employed in an industrial setting or a transportation setting, such as, for example, but not limited to, a baggage scanning system for an airport or other transportation center. 
         [0020]    In some configurations, detector array  18  is a multirow detector array. Radiation source  14  and multirow ray detector array  18  are mounted on opposing sides of gantry  12  so that both rotate about an axis of rotation. The axis of rotation forms the z-axis of a Cartesian coordinate system having its origin centered within x-ray beam  16 . The plane defined by the “x” and “y” axes of this coordinate system thus defines a plane of rotation, specifically the plane of gantry  12 . 
         [0021]    Rotation of gantry  12  is measured by an angle from arbitrary reference position within plane of gantry  12 . The angle varies between 0 and 2π radians. X-ray beam  16  diverges from the gantry plane by an angle θ and diverges along the gantry plane by angle φ. Detector array  18  has a generally arcuate cross-sectional shape and its array of detector elements  20  are arranged to receive and make intensity measurements along the rays of x-ray beam  16  throughout the angles of and of radiation beam  16 . 
         [0022]    Detector array  18  comprises a 2-D array of detector elements  20  arranged in rows and columns. Each row comprises a plurality of detector elements  20  extending generally along an in-slice dimension. Each column comprises a plurality of detector elements extending generally parallel to the z-axis. 
         [0023]    A technical effect of the present invention is the display of high resolution image areas within a relatively low resolution image. This effect is achieved in some configurations by an operator operating the CT imaging apparatus (or another apparatus on which projection data is used to generate images) using image segmentation to locate at least one volume of interest that is then reconstructed using a high resolution algorithm. The high resolution image replaces the low resolution image portion of the volume of interest for clinical study of the overall low resolution image and the high resolution volume of interest. 
         [0024]      FIG. 3  is a flow chart of an exemplary method  300  of improving segmentation, classification and quantification of small plaque deposits using an application driven optimum keyhole reconstruction technique in accordance with an embodiment of the present invention. Method  300  includes acquiring  302  CT image data of, for example, a heart at a display field of view that covers the whole heart. Images of the heart are reconstructed  304  from the acquired data. After the original CT volume has been acquired, the reconstructed images are used to identify  306  possible volumes of interest using one or more of a plurality of processes. In the exemplary embodiment, the images are automatically segmented  308  to identify areas of potential plaque buildup. In an alternative embodiment, the volumes of interest are manually selected by a user while viewing the images. In still another embodiment, potential volumes of interest are identified and the user verifies the volumes of interest and selects the volumes of interest of greatest interest to the user. The volumes or images to be reconstructed with specific adaptively determined parameters are selected  310 . The volume of reconstruction of each region can be now determined from the system. The reconstruction parameters that are optimum for each volume and study can be determined from system. The reconstruction and scan parameters are sent to  312  to a reconstruction sub-system to make only the images that correspond to each volume of interest at the desired optimum resolution for quantification. This could create new images which will contain the regions of interest selected at the highest possible resolution afforded by the scanner. 
         [0025]    The high resolution images can be reconstructed  314  by changing the display field of view to the minimum allowable for the system configuration or by using higher resolution reconstruction kernels. Once the high resolution images are created, these new volumes are analyzed  316  for accurate segmentation and classification of the lesions and the application specific quantification of physiological parameters are generated from these high resolution volumes. Examples of some measurements include volume, location, density, composition, taper, length of each lesion. The percentage of stenosis, negative and positive remodeling of the wall of the lumen can also be quantified accurately from the new high resolution images. Similarly small airway wall thickness, diameter, lumen area, wall area can be determined accurately from the high resolution images. In another exemplary embodiment, the high resolution images are superimposed on the original resolution volume to visualize the volumes of interest in high resolution. 
         [0026]      FIG. 4  is a flow chart of an exemplary method  400  of enhancing accuracy of small airway measurements using adaptive interactive workflow-based optimum volume reconstruction in accordance with an embodiment of the present invention. Method  400  includes an ability to automate the creation of optimally reconstructed images of a volume of interest for accurately measuring small airways of a patient lung. Method  400  includes acquiring  402  an initial diagnostic quality set of image data. CT images are reconstructed  404  for the lung at selected clinical reconstruction parameters and an initial airway tree segmentation is performed  406 . The initial airway tree is visualized by the user in the application at any orientation. In the exemplary embodiment, after the initial segmentation, the user can use a semi-automated approach or automated approach to define clinically relevant/clinical study specific segments of interest along the airway tree. The user can then select any airway location for measurement, or an automatic measuring protocol may be invoked, for example, but not limited to measuring a halfway point on each airway segment in the airway tree. A center of reconstruction and a volume of reconstruction around the measurement location on airways in the lung are selected  408  from the information. The volume of reconstruction parameters will be optimally built based on the available system resolution, degree of resolution needed, size of the airway needed to be measured, reconstruction kernel used for the original diagnostic images. Optimal reconstruction thresholds are selected  410  based on for example, but not limited to system resolution, original image parameters, and accuracy requirements. The resultant information about the volume of reconstruction is transmitted to the reconstruction subsystem and the new images are reconstructed using the specifications laid out by the application. The small volumes of interest are reconstructed  412  at the higher optimal resolution. The new high resolution volumes of interest images are analyzed  414  and the measurements for the airways are completed and reported  416  and/or displayed  418 . When the images are completed, the application will be able to load these volumes one at a time and analyze for the measurements of the airway parameters on the optimally reconstructed images. 
         [0027]    Other exemplary embodiments of optimal reconstructions that are available include but are not limited to: 
         [0028]    1. Performing a high-resolution reconstruction of the small volume around the airway limited by the system resolution, to get more voxels for analysis of the walls and lumen. 
         [0029]    2. Selecting between reconstruction kernels that are optimized for quantification and diagnostic reading. For example, images reconstructed using a lung kernel may have characteristics that are not optimal for quantification but the lung kernel may perform well for diagnostic reading. Regions that are to be measured can be reconstructed using a quantification-friendly kernel and analyzed for reporting the results. Clinical studies have shown that the reconstruction kernel used for diagnostic visualization/reading may not be the most optimum and accurate one for quantitative measurements. 
         [0030]    In one embodiment, the high-resolution volumes at each measurable location are bookmarked in the dataset when available and these images are used for visualizations of the entire lung and the high resolution images are used in a multi-resolution visualization mode. A complete set of high-resolution images for every airway that are measured would require memory space and computing power that exceed known system capabilities. Rather, the methods in accordance with various embodiments of the present invention provides higher resolution images but only at the small volume of interest around the airways or plaque lesions to be measured that have been selected automatically or manually. 
         [0031]      FIG. 5  is a screen shot  500  of a multi-resolution image of a phantom  502  generated using an embodiment of the present invention. Phantom  502  includes a structure that simulates a patient chest cavity  504  including a first lung cavity  506  and a second lung cavity  508 , a heart cavity  510  and a heart structure  512 . Heart cavity  510  includes a coronary vessel structure  514  that includes a generally spherical cross-section of contrast material and a plaque lesion  515  along an outer periphery  516  of vessel structure  514 . Screen shot  500  also includes a high resolution enlarged area  518  of a portion of phantom  502 . Area  518  shows a high resolution image of the low resolution original image of phantom  502  wherein a volume of interest was identified. The identification is done using automatic segmenting and analyzing of the low resolution image or by manual selection by a user, or a combination of both techniques. For example, an automatic segmenting and analyzing of the low resolution image using image parameters specified by a user or using predetermined standard parameters may be performed. A list of likely volumes of interest may be identified based on the image parameters and sorted according to a probability of meeting all the image parameters. The user may then select a volume of interest based on the list or a slideshow of the identified potential volumes of interest may be viewed. 
         [0032]    Area  518  is a high resolution image of only a portion of chest cavity  504 . Accordingly, the data memory and computing power requirements for generating and storing the high-resolution region image is significantly less than for generating and storing high resolution images of the entire chest cavity or portion thereof at high resolution. Maintaining the low resolution portion of the multi-resolution image also permits a user an overall view of the patient including any landmarks that may be used to facilitate clinical study of the image. Plaque lesion  515  may be analyzed using many more voxels in high resolution enlarged area  518  than is available in the low resolution portion of the image. Such high resolution facilitates identification and quantification of the various dimensions and the composition within that region associated with lesion  515 . 
         [0033]    The above-described imaging methods and systems are cost-effective and highly reliable. The various embodiments of the present invention provides, for example, an optimum high resolution reconstruction of only selected regions/volumes of interest to achieve more accurate segmentation and quantification of plaque regions, the use of selective reconstruction to obtain high resolution images of only the volumes of interest that are to be segmented, classified and measured accurately, and a mechanism to do an optimum reconstruction of only regions/volumes of interest and achieve better quantification of very small airways that are crucial for early airway disease detection 
         [0034]    The imaging methods and systems also provide an optimized iterative reconstruction driven by post processing algorithms in the image space, clinical study specific protocols to extract the imaging system resolution, an optimized workflow to leverage the available resolution in the scan file, and the imaging methods and systems provide a workflow that allows the quantification and diagnostic reading from same scan but without significantly increasing the number of images. Accordingly, the imaging methods and systems described above facilitate operation of imaging systems in a cost-effective and reliable manner. 
         [0035]    While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.