US 7492931 B2
A technique is provided for analysis of image datasets acquired at different points in time. Computer aided algorithms are implemented for identification and classification of features of interest, and for comparison of such features which have evolved over time as represented by the image data. The algorithms may be specifically adapted to analyze temporal change images. Such algorithms may also be used to efficiently launch temporal change analysis only when particular features of interest are possibly present in the image data.
1. A method for analyzing image data comprising:
generating a temporal change image based upon first and second images from different times by segmenting the first and second images and registering at least a portion of the segmented images with one another, wherein the first and second images are generated by different imaging modalities; and
analyzing the temporal change image via at least one CAD algorithm.
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8. A method for analyzing image data comprising:
analyzing a first image via at least one CAD algorithm to identify a feature of interest;
if a feature of interest is identified in the first image, accessing a second image from a different time than the first image and generating a temporal change image based upon the first and second images; and analyzing the temporal change image via a second CAD algorithm different from the CAD algorithm used for analyzing the first image: wherein the CAD algorithm used for analyzing the first image has a sensitivity and a specificity to produce a desired level of positive identifications of potential features of interest, and wherein the CAD algorithm used for analyzing the temporal change image is configured to reduce the positive identifications of features of interest.
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14. A method for analyzing image data comprising:
analyzing a first image via at least one CAD algorithm to identify a feature of interest; and
if a feature of interest is identified in the first image, accessing a second image from a different time than the first image and analyzing the first and second images; wherein analyzing the first and second images includes Quantifying a change in a feature of interest between the first image and the second image.
15. A system for analyzing image data comprising:
means for generating a temporal change image based upon first and second images from different times by segmenting the first and second images and registering at least a portion of the segmented images with one another, wherein the first and second images are generated by different imaging modalities; and
means for analyzing the temporal change image via at least one CAD algorithm.
16. A system for analyzing image data comprising:
means for analyzing a first image via at least one CAD algorithm to identify a feature of interest;
means for accessing a second image from a different time than the first image if a feature of interest is identified in the first image, and for generating a temporal change image based upon the first and second images; and means for analyzing the temporal change image via a second CAD algorithm different from the CAD algorithm used for analyzing the first image: wherein the CAD algorithm used for analyzing the first image has a sensitivity and a specificity to produce a desired level of positive identifications of potential features of interest, and wherein the CAD algorithm used for analyzing the temporal change image is configured to reduce the positive identifications of features of interest.
17. A system for analyzing image data comprising:
means for analyzing a first image via at least one CAD algorithm to identify a feature of interest; and
means for accessing a second image from a different time than the first image if a feature of interest is identified in the first image, and for analyzing the first and second images; wherein analyzing the first and second images includes quantifying a change in a feature of interest between the first image and the second image.
18. A computer-readable medium embodied with a computer program for analyzing image data comprising:
code stored on the computer-readable medium for generating a temporal change image based upon first and second images from different times by segmenting the first and second images and registering at least a portion of the segmented images with one another, and analyzing the temporal change image via at least one CAD algorithm, wherein the first and second images are generated by different imaging modalities.
19. A computer-readable medium embodied with a computer program for analyzing image data comprising:
code stored on the computer-readable medium for analyzing a first image via at least one CAD algorithm to identify a feature of interest, and if a feature of interest is identified in the first image, accessing a second image from a different time than the first image and generating a temporal change image based upon the first and second images, and for analyzing the temporal change image via a second CAD algorithm different from the CAD algorithm used for analyzing the first image; wherein the CAD algorithm used for analyzing the first image has a sensitivity and a specificity to produce a desired level of positive identifications of potential features of interest, and wherein the CAD algorithm used for analyzing the temporal change image is configured to reduce the positive identifications of features of interest.
20. A computer-readable medium embodied with a computer program for analyzing image data comprising:
code stored on the computer-readable medium for analyzing a first image via at least one CAD algorithm to identify a feature of interest, and if a feature of interest is identified in the first image, accessing a second image from a different time than the first image and analyzing the first and second images, wherein analyzing the first and second images includes quantifying a change in a feature of interest between the first image and the second image.
The present invention relates generally to a field of imaging systems. In particular, the invention relates to a technique for analyzing image data to recognize features of interest and comparing resulting analyses with similar analyses performed on image data collected at different points in time in computationally and workflow-efficient manners.
Many applications exist for digital imagery. Such applications range from medical diagnostic imaging to part detection and analysis, parcel screening, and so forth. Similarly, many different types of imaging systems are currently available, some of which span certain of these applications. Imaging systems range from traditional photographic systems to much more complex magnetic resonance imagine (MRI) system, computed tomography (CT) systems, positron emission tomography (PET) systems, ultrasound systems, X-ray systems, and so forth. In each of these systems, some type of image data acquisition circuitry detects input data which is used to codify individual picture elements or pixels in a matrix. When reconstructed, the pixels can be viewed in a composite image which is useful to the viewer for various intended purposes.
Regardless of the origin of pixilated image data, many new uses are being explored which enhance the usefulness of the data for various purposes. For example, in medical imaging, as well as in other fields, such as parcel inspection, image data is analyzed to recognize structures encoded in the pixels, that may be representative of features of particular interest. In the medical field these may include specific anatomies, anomalies, pathologies, and so forth. In automated computer aided or computer assisted processes, computers can now identify certain such features which can be highlighted to a user to augment or aid in diagnosis and treatment of disease, or to analyze various states of wellness. Similarly, in other contexts, such automated recognition and classification processes can greatly assist human viewers and readers by pointing out potential objects of concern or interest.
In many contexts, particularly in medical imaging, images are created of the same subject or anatomy at different points in time. Certain of these images may depict anatomies or anomalies, such as growths, lesions, or other conditions which change over time. The detection of change in medical images of a patient acquire two different instances in time would be of great potential for improving diagnosis and treatment of disease, and for monitoring response to such treatment. More generally, however, such change can be useful in tracking development and growth, or for providing an indication of any meaningful change overtime, both within and outside the medical context. Certain, “temporal subtraction” applications have been proposed. In certain such applications dissimilarity between images is calculated using a simple pixel-by-pixel subtraction approach of registered images. However, simple subtraction results in images of poor contrast. Moreover, such approaches are not sufficiently robust when two initial images are acquired using different techniques or modalities. Moreover, such approaches do not incorporate an indication of a confidence level in the magnitude of the dissimilarity measurement.
In a temporal change image, resulting pixel values, which may be displayed as gray levels in a monochrome image, or proportional to the difference or dissimilarity in pixel values between two input images acquired with temporal separation. The input images may require registration and may be processed to compensate for several factors, such as the difference in positioning of the subject during two image acquisition sessions, differences in acquisition parameters, differences in bit resolution of the images, and differences in any pre- or post-processing that may have been applied to images. Any errors in registration of the two images may result in significantly large values in the dissimilarity image due to the presumption that much more significant changes have occurred in the images or between the images due to the misalignment. For example, if the resulting registration is not perfect, the temporal analysis image of the subject resulting from two identical images will not be a zero-value image as would be anticipated given the identity of the images. That is, for identical images, the process should result in no contrast whatsoever in the dissimilarity image. These non-zero elements of the dissimilarity image represent artifacts that could be mistaken for temporal change in the subject. Such artifacts and the lack of standard anatomical features renders radiographic interpretation of temporal subtracted images challenging for a radiologist or other user, especially when given the unfamiliarity of such users with the appearance of such images. In general, a dissimilarity image summarizes only differences between two compared images. Thus, unlike conventional images that reproduce aspects of a subject in an intuitive manner, this similarity images will generally only illustrate changes in the subject as dark or light regions, lines, and so forth. The images can, of course, be superimposed or otherwise associated with the original images, although developments in the field have not risen to a level as yet to satisfactory in this regard.
The advent and proliferation of digital imaging has enabled rapid electronic access to a variety of information, particularly patient information in the medical field, and the ability to perform rapid advanced image processing and analysis. For example, integration of digital acquisition coupled to a data repository in a hospital or other network enables rapid calculation and display of temporal change images. In addition, these technologies have enabled the practical use of computer aided detection and diagnosis (CAD) techniques and radiology. Such techniques generally serve to identify and classify various features of interest reproduced or detectable within the image data. Such “machine vision” tools have been developed to improve sensitivity, specificity and efficiency of radiologists in the interpretation of images.
Little or nothing has been done in the field, however, as yet for enhancing the utility of temporal change images, that is, images compared to one another and analyzed to detect evolution of features or other changes within the images. There is a need, at present, for further enhancement in the existing techniques, and creation of new techniques for performing complex analyses of images taken at different points in time so as to provide a useful indication of changes occurring in an image subject.
The present invention provides a novel technique for analysis of images created at different points in time designed to respond to such needs. The technique may be used for images from any suitable modality or imaging system, including complex imaging systems used in medical part and parcel inspection, but also conventional photographic systems. The present technique provides for accessing image data representative of a subject created at different points in time, the points in time being separated by any useful span, from fractions of a second to months or even years. The technique also greatly facilitates the workflow and efficiency in carrying out the process of comparison and analysis. In particular, CAD techniques may be applied both for the original screening of image data for analysis, as well as to launch such screening where appropriate.
Turning now to the drawings and referring first to
In the diagrammatical view of
The imager control circuitry 16 and the image data acquisition circuitry 18 are generally regulated by some type of system control circuitry 20. Again, depending upon the nature of the imaging system and the physics involved, the system control circuitry may initiate imaging sequences by exchanging appropriate signals with the imager control circuitry 16. The system control circuitry 20 may also receive the raw or pre-processed image data from the image data acquisition circuitry 18. The system control circuitry 20 may, particularly in more complex systems, be coupled to an operator workstation 22 where an operator selects, configures, and launches examination or imaging sequences. The image data, either raw, partially processed or fully processed, is typically stored in some type of storage media as represented at reference numeral 24. In the present context, such storage media may be part of the system control circuitry 20, the operator workstation 22, or any other component of the overall system. In a medical diagnostics context, for example, such storage media may include local and remote memory, both magnetic and optical, and may include complex picture archive and communication systems (PACS) designed to store and serve image data upon demand.
In the illustration of
The imaging system 10, and indeed other imaging systems of the same or different modalities, is used to create images of a subject at various points in time. In accordance with the present technique, these images may be accessed, analyzed and compared to determine whether certain particular features are likely present in the image and therefore in the subject. Moreover, temporal change analysis in accordance with the present techniques permits identification of trends in the development of particular features of interest. In the medical diagnostics context, for example, such temporal change analysis can be used to detect the appearance, growth or reduction of certain anatomical features, disease states, naturally occurring or foreign bodies and objects, and so forth.
System 32 further includes image data processing circuitry 40. In general, the image data processing circuitry 40 will include various hardware, firmware and software designed to carryout the functions described herein. The processing circuitry may be designed around a general purpose computer or an application-specific computer. Moreover, the image data processing circuitry may, in practice, be a part of the acquisition system 10, or may be completely separate from the acquisition system. Indeed, the image data processing circuitry 40 may perform its operations in near real time as images are acquired by the acquisition system 10, or may perform operations solely in post-processing, by accessing image sets 36 and 38 from the repository 34.
Circuitry 40 draws upon one or more computer aided detection (CAD) or computer aided diagnosis algorithms as represented generally at reference numeral 42 in
System 32 will typically include an operator workstation 22 which may be the same operator workstation as that described above with reference to the imaging system 10, or a different operating station. The operating station may, itself, incorporate the image data processing circuitry 40 and may be entirely remote from the acquisition system 10. Some type of output system 44 is typically included, such as for creating hardcopy outputs images, reports, and so forth. Either operator workstation 22 or output system 44 will also include monitors for viewing reconstructed and temporal change images as discussed below, which may be presented in the form of high resolution and high contrast images permitting users and viewers to analyze, read, annotate and otherwise use the reconstructed images. System 32 implements one or more types of processing for analyzing temporal changes between images taken at different points in time.
Image acquisition at block 48 of
Preprocessing module 56 may serve several functions, depending upon the nature of the image data. For example, module 56 may “normalize” two images to account for differences in acquisition techniques or differences in pre- and post-processing methods. As an example, in X-ray images, if the first image has half the exposure of the second image, gray levels in the first image may be multiplied by a factor of 2 before any further comparison to the second image. The adjustment in the images serves to reduce the differences in the overall image intensity due to image display or technical factors such as differences in dose. Preprocessing module 56 may also perform operations such as scaling, size and orientation adjustments, dynamic range adjustments, and so forth.
Segmentation module 58 identifies and defines the limits of features of interest in the image data at both points in time. Many types of segmentation are currently available in the art, and these processes are typically identify gradients, intensities and other characteristics of the pixilated data to extract meaningful associations of the data, such as to identify edges, areas, regions, and so forth which may represent recognizable features in the ultimate image. Module 58 therefore provides an automated or manual mechanism for isolating regions of interest in the image data. In many cases of practical interest, the entire image could be the reason of interest, with specific features or subsets of data being identified as potentially representing objects of particular interest.
Registration module 60 provides for alignment of similar regions or objects of interest in the images taken at different points in time. If the regions of interest for temporal change analysis are small, rigid body registration transformations, including translation, rotation, magnification and shearing may be sufficient to register a pair or images taken at two different points in time. However, if the regions of interest are large, including almost the entire image, warped, elastic transformations can be applied.
As will be appreciated by those skilled in the art, one manner for implementing the warped registration is the use of multi-scale, multi-region, pyramidal approach. In such approaches, a different cost function highlighting changes may be optimized at every scale. Such cost functions can be, but are not limited to, correlation methods, such as mathematical correlation and sign-change measurement, or statistical methods such as entropy measurements and mutual information. Images are re-sampled at a given scale and then divided into multiple regions. Separate shift vectors are calculated for different regions. Shift factors are interpolated to produce a smooth shift transformation, which is applied to warp one of the images. Weighting functions on shift vectors may be applied during interpolations and these weighting functions can be determined from the image characteristics, such as anatomical features, or the characteristics of the cost function map. The images are re-sampled and the warped registration process is repeated at the next higher scale until the pre-determined final scale is reached, or a point is reached where the cost function map has attained a certain pre-determined threshold. In other situations, a combination of rigid registration and elastic transformations may be used.
Following registration by the registration module 58, the images at different points in time will be comparable. The preprocessing segmentation and registration modules also serve to render the images comparable insomuch as they reduce apparent but inconsequential differences between the images that could tend to indicate more substantial changes over time than have actually occurred in the subject. Comparison module 62, then, analyzes dissimilarities between the images. A dissimilarity measure between the registered images may be performed in any one of several ways. For example, simple subtractions may be employed, wherein differences are analyzed on a pixel-by-pixel basis and an absolute value of a difference is recorded. However, enhanced methods include a division method, in which the difference between the images, on a pixel-by-pixel basis may be represented by the equation:
Following comparison of the images, the display and report module 54 provides a display and quantification capabilities for the user to visualize or quantify the results of the temporal comparison. Results of temporal comparisons may be simultaneously displayed on a display device, such as a monitor, separate from either of the temporal images. Alternatively, either or both of the temporal images may be superimposed with one another and with the temporal change image via a logical operator based on a specified criterion. For quantitative comparison, color look-up tables for the overlaid images may be used so as to highlight differences or changes that have occurred over time. The resulting combination can be presented in a monochrome or multi-color overlay display.
In the temporal change analysis routine illustrated in
The present technique also provides for quantitative analysis of temporal changes between images.
As noted above, the present technique may be employed with a reconciliation routine in which a machine or human reader identifies discrepancies between analyses. Such discrepancies may typically include concurrences and differences, such as in the recognition or classification of features of interest in temporally distinct images.
In the various processes and workflows described above, various types of CAD algorithms will be implemented. As will be appreciated by those skilled in the art, such CAD processing may take many forms, depending upon the type of analysis, type of image, and type of feature of interest.
In the implementation of CAD routine 94 illustrated in
A feature extraction module 100, which may be an optional module in the routine, involves performing computations on the sourced data. For example, the image-based data in the region of interest may be analyzed to determine statistics such as shape, size, density, curvature, and so forth. On acquisition-based and patient-based data, such as that used in the medical context, the data itself may serve as the extracted features.
Once the features are segmented and any feature extraction has been performed as desired, a classification module 102 helps to classify the regions of interest in accordance with any suitable type of classification. For example, in the medical context, masses may be classified by their type, by a probability that they are benign or malignant, and so forth. Such classifiers may include a wide range of algorithms, such as Bayesian classifiers, neural networks, rule-based methods, fuzzy logic methods, and so forth. It should be noted that the CAD routine is performed once by incorporating features of all data and can be performed in parallel. The parallel operation of CAD algorithms may improve performance of the CAD operations. For example, individual operations on the datasets may be influenced by results of individual modules of the CAD algorithm or by combining the results of CAD operations, through logical operators such as AND, OR NOT operations, or combinations of these. In addition, different CAD algorithms and operations may be implemented to detect multiple features, articles, disease states, and so forth in series or in parallel, as described more fully below with reference to
It should be noted that the CAD routine may make use of specific information relating to the images, or general information relating to knowledge with respect to particular features of interest anticipated in the images for the feature extraction and classification steps, as well as for segmentation. As illustrated in
In a preferred process, some type of training of the CAD algorithm is provided, such as through the incorporation of prior knowledge of known and confirmed features of interest. Training phases of this type may involve computation of several candidate features based on known samples, such as benign and malignant masse in the medical context. A feature selection algorithm is then employed to sort the candidate features and select only the useful features for confirming or rejecting certain segmentation, feature extraction and classification candidates. Only useful features or characteristics are preferably retained to reduce redundancy and to improve computational efficiency. Such decisions are typically based on classification of results with different combinations of candidate features. The feature selection algorithm employed is also used to reduce the dimensionality from a practical standpoint, therefore further improving computational efficiency. A feature set is thus derived that can optimally discriminate between features of interest, such as benign and malignant masses in the medical context. This optimal feature set is extracted on regions of interest in the CAD routine. Optimal feature selection can be performed using many techniques, such as well-known distance measure techniques, including diversions measures, Bhattacharya distance measures, Mahalanobis distance measures, and so forth.
The CAD algorithms employed in the present technique may be different from one another, and indeed multiple different CAD algorithms may be used. For example, as described above, algorithms may be used for parallel analysis of image data, or may be used in series, such as to launch temporal analysis only where particular features of interest may be present or viewable in the image data. Parallel CAD algorithms may also be employed for the same or different features, or with different levels of sensitivity and specificity, with reconcilers being employed as discussed above, where appropriate. Moreover, as noted above, it is anticipated that temporal analysis CAD algorithms will continue to be developed for operation on temporal change images specifically. These will include algorithms for quantitative analysis of changes over time.
As also mentioned above, certain CAD algorithms may be performed or implemented in parallel as represented generally in
While the invention may be susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and have been described in detail herein. However, it should be understood that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the following appended claims.