WO1999054705A2 - Iterative warping for temporal subtraction of radiographs - Google Patents
Iterative warping for temporal subtraction of radiographs Download PDFInfo
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
- G06T7/00—Image analysis
- G06T7/0002—Inspection of images, e.g. flaw detection
- G06T7/0012—Biomedical image inspection
- G06T7/0014—Biomedical image inspection using an image reference approach
- G06T7/0016—Biomedical image inspection using an image reference approach involving temporal comparison
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Definitions
- the present is related to automated techniques for automated detection of abnormalities in digital images, for example as disclosed in one or more of U.S. Patents 4,839,807; 4,841,555; 4,851,984; 4,875,165; 4,907,156; 4,918,534; 5,072,384; 5,133,020; 5,150,292; 5,224,177; 5,289,374; 5.319,549; 5,343,390; 5,359,513; 5,452,367; 5,463.548; 5,491,627; 5,537,485; 5.598,481 ; 5,622,171; 5,638,458; 5,657,362; 5,666,434; 5.673,332; 5,668,888; as well as U.S.
- the present invention also relates to technologies referenced and described in the references identified in the appended APPENDIX and cross-referenced throughout the specification by reference to the number, in brackets, of the respective reference listed in the APPENDIX, the entire contents of which are also incorporated herein by reference.
- Various of these publications may correspond to various of the cross-referenced patents and patent applications.
- the present invention is related to temporal analysis of medical images and, in particular, to the analysis of chest radiograph images using automated temporal subtraction. Discussion of the Background
- radiologists For the interpretation of chest radiographs, radiologists commonly compare a current film with previous films in order to facilitate the detection of abnormalities on chest radiographs, such as pulmonary nodules, interstitial infiltrates, pleural effusions, and cardiomegaly.
- abnormalities on chest radiographs such as pulmonary nodules, interstitial infiltrates, pleural effusions, and cardiomegaly.
- investigators at the University of Chicago Department of Radiology have developed a temporal subtraction scheme based on a nonlinear geometric warping technique.
- Another object of this invention is to provide a novel image processing technique to overcome severe misregistration errors mainly due to differences in a subject's inclination and/or rotation in temporally sequential images.
- a further object of this invention is to provide a novel temporal image subtraction technique to assist radiologists in the detection of interval changes on chest radiographs.
- the method includes the steps of (a) determining first shift values between pixels of a first digital image and corresponding pixels of a second digital image; (b) warping said second digital image based on the first shift values to obtain a warped image in which spatial locations of pixels are varied in relation to said first shift values; (c) determining second shift values between pixels of said first digital image and pixels of said warped image obtained in step (b); (d) wa ⁇ ing said warped image obtained in step (b) based on the second shift values to obtain an iteratively wa ⁇ ed image in which spatial locations of pixels of said wa ⁇ ed image obtained in step (b) are varied in relation to said second shift values; and (e) subtracting the iteratively wa ⁇ ed image from said first digital image.
- initial shift values are obtained by cross- correlation techniques using a template and search regions of interest. Shift vectors and a histogram of shift vectors are obtained from each initial shift value. Based on the histogram of shift vectors, variations in various groups of the initial shift values are smoothed using two-dimensional fitting.
- the present invention similarly includes a computer readable medium storing program instructions by which the method of the invention can be performed when the stored program instructions are appropriately loaded into a computer, and a system for implementing the method of the invention.
- Figure 1 is an illustration of selecting different ROIs for analysis of histograms of subtraction images.
- Figures 2(a)(A) and 2(a)(B) are photographs of subtraction images with ROI placement for analysis of histograms for pixel values, with the photograph of Fig. 2(a)(A) being an example of a poor subtraction image and the photograph of Fig. 2(a)(B) being an example of a good subtraction image.
- Figure 2(b) is a graph of histograms of subtraction images of Figures 2(a)(A) and 2(a)(B).
- Figure 3(a)-3(e) are illustrations of distributions of histogram widths in both lungs for cases rated as (a) 1 (very poor quality), (b) 2 (poor quality), (c) 3 (adequate quality), (d) 4 (good quality), and (e) 5 (excellent quality), respectively.
- Figure 4(a) is a schematic diagram of the temporal subtraction method using an iterative wa ⁇ ing technique according to the present invention.
- Figures 4(b)-4(d) are highly schematic diagrams of shift vector analysis, first wa ⁇ ing, and second wa ⁇ ing steps, respectively, included in the method of Figure 4(a).
- Figures 4(e) 1 and 4(e)(2) illustrate in more detail than the highly schematic Figures 4(a)-4(d) the processing performed in the iterative process of the present invention.
- Figures 5(a) and 5(b) are photographs of respective subtraction images obtained using different shift vectors, i.e., (a) good subtraction image and (b) a poor subtraction image, wherein shift vectors are overlaid on each image, dark and light vectors (short lines) are used for inside and outside, respectively, of approximate lung areas, and small white dots at one end of dark vectors indicate initial locations of template ROIs, which are used in the wa ⁇ ing technique
- Figures 6(a) and 6(b) are graphs respectively illustrating a distribution of accumulated shift vector values as a function of shift vector orientation for (a) a good subtraction case and (b) a poor subtraction case.
- Figures 7(a)-7(d) are photographs respectively illustrating (a) dominant shift vectors (dark lines) in a temporal image, (b) subtraction image; (c) remaining shift vectors (dark lines) and (d) a subtraction image.
- Figures 8(a), 8(b) and 8(c) are photographs of subtraction images respectively obtained with (a) a single wa ⁇ ing technique, (b) an iterative wa ⁇ ing technique, and (c) an iterative wa ⁇ ing technique plus linear inte ⁇ olation of shift values.
- Figures 9(a), 9(b), 9(c), (d), and 9(e) are graphs respectively illustrating distributions of histogram widths in both lungs for the 181 cases, obtained with the prior wa ⁇ ing technique (dots) and the wa ⁇ ing technique of the present invention (x), rated as 1 (very poor quality), 2 (poor quality), 3 (adequate quality), 4 (good quality), and 5 (excellent quality).
- Figures 10(a) and 10(b) are photographs of subtraction images for comparison, respectively obtained (a) with the prior wa ⁇ ing technique and (b) with the wa ⁇ ing technique of the present invention.
- Figure 11 is a bar graph illustrating the distribution of the degree of improvement, with the subjective rating method, in the quality of the subtraction images obtained with the wa ⁇ ing technique of the present invention.
- Figure 12 is a schematic illustration of a general pu ⁇ ose computer 100 programmed according to the teachings of the present invention.
- the image database used in the derivation of the present invention included 181 pairs of chest radiographs obtained from the Iwate Prefectural Hospital, Morioka, Japan. These 181 cases were obtained sequentially from chest screening images which were made with a Fuji Computed Radiography (FCR) system (Fuji Medical Systems Co., Ltd., Tokyo, Japan). The time interval between the current and previous images for all cases was 1 year. The pixel size and gray level of CR chest images were 0.2 mm and 1024, respectively.
- the technique of the present invention was developed by use of a Silicon Graphics 02 workstation. Methodology 1. Subjective evaluation of the quality of subtraction images
- the final rating for each case was determined in one of the five categories above based on the average (or the majority) of all observers' ratings.
- Figs. 1(a)- 1(d) For determination of the histogram of pixel values in each lung field of the subtraction image, various ROIs of different size and shape in each lung were examined, as shown in Figs. 1(a)- 1(d). Initially, the ROI included all of the lung and mediastinum areas, as illustrated in Fig. 1(a). Second, we segmented the fight and left lungs were segmented by using the heart border information, as shown in Fig. 1(b), in order to evaluate the quality of the subtraction image in each lung field separately. However, it was found that the top and the bottom areas of the ROIs tended to include misregistration errors caused by the difference between the clavicle positions, and also the difference between different diaphragm levels, respectively.
- the areas around the ribcage edge boundaries and the boundaries of the mediastinum were excluded from the ROIs, as shown in Fig. 1(c).
- small ROIs as shown in Fig. 1(d) were employed, because the extent of the misregistration error for the ribs can be detected more sensitively with the ROI placed over the central area of the lung rather than with the other ROIs shown in Figs. 1(a), 1(b), and 1(c).
- the size of the small ROIs for both lungs was 30 pixels (width) x 120 pixels (length).
- the centers of the ROIs were determined by using the x,y coordinates of the ribcage edges and the cardiac edges.
- the vertical locations of the two centers of the ROIs were the same and equal to the y-location between the top lung, which was obtained from the ribcage edge detection scheme, and the bottom of the right ribcage edge.
- the horizontal centers of the ROIs were determined as the x-location in each lung between the ribcage edge and the cardiac edge, at the vertical center level of the ROIs.
- Figure 2 (a) shows a comparison of a poor (A) and a good (B) subtraction images of the right lung.
- the ROIs used for determination of the histogram width are illustrated by black lines.
- the corresponding histograms of these images are shown in Figure 2 (b). It is seen that the width of the histogram for the poor subtraction image (A) is much wider than that for the good subtraction image (B).
- the "misregistration" the difference between an abnormal current image and a normal previous image
- due to the actual interval abnormal change would usually be localized and small compared with the misregistration errors due to a failure in image matching. Therefore, the quality of the subtraction image was evaluated by using the widths of the histograms in the ROI for each lung.
- the width of the histogram at 10%) of the largest peak was obtained. It was found that the width of the histogram at a low level such as 10%> of the peak was more sensitive than the histogram width at a high level in distinguishing between good and poor subtraction images.
- the distributions of the histogram widths for each of the five groups of different qualities of subtraction images, which were grouped based on subjective ratings, obtained by the previous technique are shown in Fig. 3 (a)-3(e). In these figures, the horizontal and vertical axes correspond to the width of the histogram in the right and the left lung, respectively.
- the histogram widths for "very poor” and “poor” subtraction images tend to be large and are distributed in the upper right, as shown in Figs. 3 (a) and 3(b).
- the histogram widths of "adequate” subtraction images are distributed in the intermediate range, as shown in Fig. 3 (c).
- the histogram widths for "good” subtraction images are shifted toward the lower left, as shown in Fig. 3 (d).
- the "excellent" subtraction images as represented by a subjective rating score of 5 are characterized by narrow histogram widths, as shown in Fig. 3 (e). 3.
- a nonlinear density correction technique [1,7] was applied first for adjustment of the density and contrast in the two digitized images, i.e., the current and previous chest radiographs.
- the difference in the lateral inclination between the two images was corrected by use of an image rotation technique.
- the global shift values were then determined for the initial registration by use of the cross-correlation of a pair of blurred low-resolution images obtained from the current and the previous image.
- a number of template ROIs 32 x 32 matrix
- the corresponding search area ROIs 64 x 64 matrix
- Shift values, ⁇ x and ⁇ y, for all pairs of selected ROIs were determined by using a cross-correlation technique to find the "best" matched areas in the current and previous images.
- a two-dimensional surface fitting by use of polynomial functions was then applied to each set of mapped shift values, ⁇ x and ⁇ y, for conversion of the x, y coordinates of the previous image, i.e., for wa ⁇ ing of the image.
- the wa ⁇ ed previous image was then subtracted from the current image.
- the temporal subtraction technique is illustrated in overview in Fig. 4 (a).
- the matrix size for the current and the previous chest image obtained with a CR system is reduced to 586 x 586 (one third of the original image matrix size).
- a density correction technique was not applied because the chest images obtained with the CR system can maintain consistent density and contrast with the use of the exposure data recognition (EDR) system [4] included in most recent CR systems.
- EDR exposure data recognition
- global matching 420 is performed using an image rotation [2], determining the angle between the two images by comparison of the two midlines of these images [5], and applying an initial image matching technique for determination of the global shift value between the two images, which corresponds to the shift in the x, y coordinates of one image relative to the other.
- the two images are globally registered by use of the initial image matching technique based on the cross-correlation of blurred low-resolution images.
- an iterative image wa ⁇ ing technique is employed to improve local image matching and thus to reduce registration errors.
- local segmentation 430 is performed in which the ribcage edges of the previous image are detected based on image profile analysis.
- the cardiac edges are determined based on an edge detection technique for segmentation of the lungs of the current image.
- the shift values ⁇ x and ⁇ y, for all of the selected ROIs are determined by a cross-correlation technique.
- Shift vectors based on the shift values ⁇ x and ⁇ y are then determined, as discussed in more detail hereinafter.
- a first image wa ⁇ ing (step 450), typically of the previous or older image, is performed to derive a first wa ⁇ ed image (step 460). Then a second wa ⁇ ing (step 470) is performed on the first wa ⁇ ed image, followed by obtaining of a subtraction image 480 for diagnosis.
- Fig. 4(b) illustrates very schematically one embodiment of determination of fitted shift values for the first wa ⁇ ing step.
- a shift vector orientation histogram is obtained (step 411) for each lung.
- step 412 peaks in the histogram of each lung are determined, and utilized to identify dominant and remaining shift vectors (step 413).
- a first wa ⁇ ing is performed.
- step 451 optimized shift values are determined and then in step 452 subjected to surface fitting [1]. After fitting, a coordinate transformation is performed in step 453 and a wa ⁇ ed image obtained in step 454.
- a second image wa ⁇ ing technique which is applied to the wa ⁇ ed previous image, is then performed.
- the optimized shift values between the current image and the wa ⁇ ed previous image are determined by the cross-correlation technique and vectors are again determined in step 471 to derive optimized shift values, as discussed in more detail hereinafter.
- a linear inte ⁇ olation is performed on the optimized shift values in step 472 to determine the final shift values on all of the x,y coordinates of the wa ⁇ ed previous image.
- Another coordinate transformation is performed in step 473 to obtain a second wa ⁇ ed image in step 474.
- the temporal subtraction image is obtained by subtraction of the second wa ⁇ ed previous image from the current chest image, as shown schematically in step 480 of Fig. 4(a). 4. Weighting factors for surface fitting of shift values
- weighting factors determined based on the cross-correlation values were used for surface fitting to determine the local shift values. [1] In general, the larger the cross-correlation value, the larger the weighting factor. However, it was found that the cross-correlation values near the ribcage borders, in the mediastinum area, and below the diaphragm area were generally very large, and much greater than the values in the lung areas.
- the fitted shift values would have been affected considerably by the shift values near the ribcage borders, in the mediastinum, and below the diaphragms area. This is not desirable, because accurate subtraction is commonly required in the lung fields rather than in other areas in chest images.
- a lung segmentation method which includes the detection of ribcage edges and heart edges for identifying the shift values in the lung area.
- a weighting factor of 1.0 is assigned for ROIs in the lung areas, and 0.25 for ROIs in the mediastinum and below the diaphragm, whereupon weighted polynomial fitting is performed. [1]
- the fitted shift values are determined for the first wa ⁇ ing step. When the new weighting factors were used, the registration errors in the lung areas were reduced in some cases. 5. Shift- vector orientation analysis
- the surface fitting technique of the shift values was generally effective in improving local registration around the poorly matched regions. [1] However, if some shift vectors with incorrect orientation are included within a relatively small region, the correct shift vectors may be affected significantly by the fitting. In the previous method [1.3], the orientation (or angle) of the shift vectors was not considered in the process for determining the surface fitting of the shift values. However, according to the present invention it has since been determined that the orientation of the shift vectors is an important factor for accurate surface fitting, and therefore two different components, i.e., the dominant and the remaining (non-dominant) shift vectors, are identified by using the shift vector orientation histogram, which is a histogram of accumulated shift values as a function of the shift vector orientation.
- the ribcage edges and the cardiac edges are determined by using the edge detection technique [6] for segmentation of the lungs.
- Many ROIs are selected in the lung field for both the previous and current images.
- Shift values, ⁇ x and ⁇ y, are determined for each pair of ROIs based on the cross-correlation technique.
- the orientation (or angle) of the shift vector for each ROI is determined by the arc tangent of ⁇ y/ ⁇ x. Then the shift- vector orientation histograms for the right and the left lung are obtained.
- Figures 5 (a) and 5(b) illustrate the distributions of shift vectors obtained with a good and a poor subtraction image, respectively.
- the orientations of the shift vectors for good subtraction images tend to be similar. This may be because the rib contrast in this chest image is relatively high, and thus the template ROI which includes a rib edge could easily match the corresponding rib edge in the search area ROI.
- the orientations of the shift vectors for a poorly registered case were varied because of the low-contrast ribs.
- the shift-vector orientation histograms of these cases, Figs. 5(a) and 5(b), for the right and left lungs are shown in Fig. 6(a) and 6(b). It is apparent that the shift-vector orientation histograms for a good registered case have a large peak in each lung. However, there is no obvious peak in the orientation histograms for a poor case, as shown in Fig. 6(b).
- FIGS 7(a) and 7(b) show the selected dominant shift vectors and the corresponding subtraction image obtained by fitting with the dominant shift vectors, respectively.
- Figures 7(c) and 7(d) illustrate non-dominant shift vectors and the corresponding subtraction image obtained by fitting with the non-dominant shift vectors, respectively. It is clear that the subtraction image obtained with the dominant shift vectors is superior to that obtained with the non-dominant shift vectors.
- Figures 8(a) and 8(b) show the temporal subtraction images obtained with the prior technique and that of the present invention using shift- vector analysis, respectively. The quality of the subtraction image obtained according to the present invention is improved slightly.
- the present invention selects for further two-dimensional fitting the fitted shift values of pixels of each respective lung region in the respective first and second wa ⁇ ed images exhibiting the narrower histogram of pixel values, and then performs further two-dimensional fitting on the further selected fitted shift values, and then wa ⁇ s the previous image using said further fitted shift values to produce a wa ⁇ ed image for further iterative processing.
- the image wa ⁇ ing technique is applied repeatedly and thus iteratively first on the previous image, next on the first wa ⁇ ed image, and then on the second wa ⁇ ed image, and so on, until the desired quality of the subtraction image is obtained.
- the second and subsequent image wa ⁇ ing steps are employed for improvement of the quality of the temporal subtraction image.
- the wa ⁇ ed previous image from the first wa ⁇ ing step is obtained.
- the current image and the wa ⁇ ed previous image are then used for the second image wa ⁇ ing.
- the shift values, ⁇ x and ⁇ y are determined by use of the cross-correlation technique for all of the selected ROIs in the current image and the wa ⁇ ed previous image.
- shift vectors and a histogram of shift vectors are derived, angular ranges determined, and two sets of shift vectors again selected for production of interim first and second twice wa ⁇ ed images.
- corresponding subtraction images are obtained, and the histograms of pixel values in each subtraction image are evaluated.
- one subtraction image exhibits a narrower histogram of pixel values in both lung regions in comparison to that of the other subtraction image, then that subtraction image is considered the final subtraction image for diagnosis (assuming that no further wa ⁇ ing iterations are to be performed). If however that is not the case, then another shift value fitting is performed.
- the present invention selects for further two-dimensional fitting the fitted shift values of pixels of each respective lung region in the respective first and second wa ⁇ ed images exhibiting the narrower histogram of pixel values, and then performs further two-dimensional fitting on the further selected fitted shift values, and then wa ⁇ s the previously wa ⁇ ed image using the further fitted shift values to produce a secondly wa ⁇ ed image for further iterative processing, if desired, or for production of the final subtraction image for diagnosis.
- the shift values of all x,y coordinates over the entire lung fields for the second image wa ⁇ ing are preferably obtained by a linear inte ⁇ olation technique instead of the surface fitting technique with polynomial functions used during the first wa ⁇ ing, since linear inte ⁇ olation was observed to result in a somewhat better subtraction image after the second image wa ⁇ ing.
- the present invention can also be practiced using linear inte ⁇ olation for the first image wa ⁇ ing or polynomial fitting for the second image wa ⁇ ing.
- Figure 8(c) shows a subtraction image obtained by application of the second image wa ⁇ ing technique.
- the registration errors for the ribs in the temporal subtraction image are reduced substantially by use of the second image wa ⁇ ing technique.
- a third image wa ⁇ ing technique which is basically the same as the second wa ⁇ ing process, can also be used.
- the quality of the subtraction image was improved slightly in some cases by applying the third image wa ⁇ ing; however, at the expense of increased computational time for the iterative wa ⁇ ing process.
- two iterations of iterative image wa ⁇ ing are preferably employed, i.e., the second image wa ⁇ ing technique is employed as a standard for local image matching.
- Figures 4(e) 1 and 4(e)(2) illustrate in more detail than the highly schematic Figures 4(a)-4(d) the processing performed in the iterative process of the present invention.
- the process begins with obtaining first and second temporal sequential digital images of a subject (step 4000). Then these first and second digital images are preprocessed in step 4010, as above discussed in connection with step 420 of Fig. 4(a).
- step 4020 initial shift values are determined by selecting plural template regions of interest (ROIs) in the first digital image and corresponding search area ROIs in the second image, and determining shift values between pixels centered in each template ROI and pixels centered in a respective search area ROI and exhibiting highest cross-correlation with respect to said template ROI, [1,3]
- step 4020 shift vectors are determined for each of said shift values; a first cumulative histogram of the shift vectors for pixels in one lung, and a second cumulative histogram of the shift vectors for pixels in the other lung are also produced.
- the shift vector histograms are used to select two sets of shift values for two-dimensional fitting.
- the process includes selecting, based on said first histogram, a first set of pixels in the one lung with shift vectors within a ⁇ 90° range of angles of a peak in the first histogram of shift vectors and selecting the second set of pixels as the remaining pixels in the one lung, and selecting, based on the second histogram, a third set of pixels in the other lung with shift vectors within a ⁇ 90° range of angles of a peak in the second histogram of shift vectors and selecting the fourth set of pixels as the remaining pixels in the other lung.
- the shift values of the first and third sets of pixels are fitted using polynomial fitting to produce a first fitted set of shift values, and likewise the shift values of the second and fourth sets of pixels are fitted using polynomial fitting to produce a second fitted set of shift values.
- the method may include selecting, based on the first histogram, a first set of pixels in the one lung with shift vectors within a ⁇ 90° range of angles of a peak in the first histogram of shift vectors and selecting the second set of pixels as the remaining pixels in the one lung (assuming a peak exists in the histogram of that lung), and selecting, based on the second histogram, a third set of pixels in the other lung with shift vectors within an arbitrary range, e.g., a 0-180° range, of angles in the second histogram of shift vectors and selecting the fourth set of pixels as the remaining pixels in the other lung (assuming a peak does not exist in the shift vector histogram for that lung), and then forming first and second sets of fitted shift values as previously noted. If no peak
- step 4040 the first and second sets of fitted shift values derived in step 4030 are used to wa ⁇ one of the original sequentially temporal images to derive two wa ⁇ ed images.
- the method then proceeds in step 4050 by producing first and second interim subtraction images between the first digital image and the two wa ⁇ ed image, respectively.
- the two interim subtraction images are then used to derive a final first wa ⁇ ed image for further iterative processing.
- the method proceeds in step 4060 to determine a histogram of pixel values in lung regions of the first and second subtraction images and to determine if one of the first and second subtraction images exhibits a narrower histogram of pixel values in both lung regions.
- the method proceeds by selecting the wa ⁇ ed image from which the subtraction image having the narrower histograms was produced for further iterative wa ⁇ ing.
- the method proceeds in step 4080 by selecting for further two-dimensional fitting the fitted shift values of pixels of each respective lung region in the respective first and second wa ⁇ ed images exhibiting the narrower histogram of pixel values, performing further two- dimensional fitting in step 4090 on the further selected fitted shift values, and wa ⁇ ing, in step 4100, the second digital image using the further fitted shift values to produce a final first wa ⁇ ed image for further iterative wa ⁇ ing.
- a further iteration of wa ⁇ ing commences between the final first wa ⁇ ed image and the other original digital image by determining shift values, shift vectors and shift vector histograms etc.
- step 4120 a subtraction image for diagnosis is produced by subtraction of the final second wa ⁇ ed image from the non- wa ⁇ ed original digital image.
- the subtraction images scored as 1 or 2 may be considered as poor and inadequate, and would need to be improved for clinical use.
- the subtraction images scored as 3, 4, or 5 are good subtraction images, which would be adequate for clinical use.
- the number of adequate subtraction images increased from 78.5% to 97.7% with the new scheme. It is clear thus that the performance of the temporal subtraction was improved substantially by use of the iterative image wa ⁇ ing method of the present invention.
- the quality of the 181 subtraction images were evaluated by using the histogram widths.
- the histogram widths for each subjective rating group are shown in Figures 9 (a)-9(e).
- the distributions of the histogram widths of the subtraction images obtained with the previous and the new temporal subtraction scheme are plotted with dots and x, respectively.
- the results show that the histogram widths of the subtraction images obtained with the iterative wa ⁇ ing method of the present invention tend to be small and distributed in the lower left on the graphs. This indicates that the misregistration errors in the subtraction images obtained with the new method are smaller than those obtained with the previous method.
- Subtraction images obtained with the previous and the new method are shown in Figs. 10 (a) and 10(b), respectively. It is apparent that the registration errors in the subtraction image obtained with the previous method are decreased substantially with the new temporal subtraction method, as shown in Fig. 10 (b).
- the relative change in the quality of temporal subtraction images was subjectively evaluated by comparing two subtraction images obtained with the previous and the new methods. Using a subjective rating scale from -2 to 2, the quality of the new subtraction image compared to the previous subtraction image is rated as +2, clearly improved;
- This invention may be conveniently implemented using a conventional general pu ⁇ ose digital computer or micro-processor programmed according to the teachings of the present specification, as will be apparent to those skilled in the computer art.
- Appropriate software coding can readily be prepared by skilled programmers based on the teachings of the present disclosure, as will be apparent to those skilled in the software art.
- the present invention includes a computer program product which is a storage medium including instructions which can be used to program a computer to perform a process of the invention.
- the storage medium can include, but is not limited to, any type of disk including floppy disks, optical discs, CD-ROMs, and magneto-optical disks, ROMs, RAMs, EPROMs, EEPROMs, magnetic or optical cards, or any type of media suitable for storing electronic instructions.
- FIG 12 is a schematic illustration of a general pu ⁇ ose computer 100 programmed according to the teachings of the present invention.
- the general pu ⁇ ose computer 100 includes a computer housing 102 having a motherboard 104 which contains a CPU 106 and memory 108.
- the computer 100 also includes plural input devices, e.g. , a keyboard 122 and mouse 124, and a display card 110 for controlling monitor 120.
- the computer system 100 further includes a floppy disk drive 114 and other removable media devices (e.g., tape, and removable magneto-optical media (not shown)), a hard disk 112, or other fixed, high density media drives, connected using an appropriate device bus, e.g., a SCSI bus or an Enhanced IDE bus.
- the computer 100 may additionally include a compact disc reader/ writer 118 or a compact disc jukebox (not shown).
- the present invention includes programming for controlling both the hardware of the computer 100 and for enabling the computer 100 to interact with a human user.
- Such programming may include, but is not limited to, software for implementation of device drivers, operating systems, and user applications.
- Such computer readable media further includes programming or software instructions to direct the general pu ⁇ ose computer 100 to perform tasks in accordance with the present invention.
- general pu ⁇ ose computer 100 may include a software module for digitizing and storing PA radiographs obtained from an image acquisition device.
- the present invention can also be implemented to process digital data derived from a PA radiograph elsewhere.
- the invention may also be implemented by the preparation of application specific integrated circuits or by interconnecting an appropriate network of conventional component circuits, as will be readily apparent to those skilled in the art.
Abstract
Description
Claims
Priority Applications (4)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
EP99917300A EP1295244A4 (en) | 1998-04-02 | 1999-04-02 | Method, system and computer readable medium for iterative image warping prior to temporal subtraction of chest radiographs in the detection of interval changes |
AU35452/99A AU3545299A (en) | 1998-04-02 | 1999-04-02 | Method, system and computer readable medium for iterative image warping prior totemporal subtraction of chest radiographs in the detection of interval changes |
CA002326776A CA2326776C (en) | 1998-04-02 | 1999-04-02 | Method, system and computer readable medium for iterative image warping prior to temporal subtraction of chest radiographs in the detection of interval changes |
JP2000545001A JP2003530722A (en) | 1998-04-02 | 1999-04-02 | Method, system and computer readable medium for iterative image distortion prior to temporal subtraction of chest radiographs in detecting temporal changes |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
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US09/053,798 US6067373A (en) | 1998-04-02 | 1998-04-02 | Method, system and computer readable medium for iterative image warping prior to temporal subtraction of chest radiographs in the detection of interval changes |
US09/053,798 | 1998-04-02 |
Publications (2)
Publication Number | Publication Date |
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WO1999054705A2 true WO1999054705A2 (en) | 1999-10-28 |
WO1999054705A3 WO1999054705A3 (en) | 2002-12-27 |
Family
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Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/US1999/004290 WO1999054705A2 (en) | 1998-04-02 | 1999-04-02 | Iterative warping for temporal subtraction of radiographs |
Country Status (6)
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US (1) | US6067373A (en) |
EP (1) | EP1295244A4 (en) |
JP (1) | JP2003530722A (en) |
AU (1) | AU3545299A (en) |
CA (1) | CA2326776C (en) |
WO (1) | WO1999054705A2 (en) |
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Also Published As
Publication number | Publication date |
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EP1295244A2 (en) | 2003-03-26 |
JP2003530722A (en) | 2003-10-14 |
CA2326776C (en) | 2008-06-17 |
CA2326776A1 (en) | 1999-10-28 |
AU3545299A (en) | 1999-11-08 |
WO1999054705A3 (en) | 2002-12-27 |
EP1295244A4 (en) | 2009-06-03 |
US6067373A (en) | 2000-05-23 |
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