We have developed a multi-probe resonance-frequency electrical impedance spectroscope (REIS) system to detect breast
abnormalities. Based on assessing asymmetry in REIS signals acquired between left and right breasts, we developed
several machine learning classifiers to classify younger women (i.e., under 50YO) into two groups of having high and
low risk for developing breast cancer. In this study, we investigated a new method to optimize performance based on the
area under a selected partial receiver operating characteristic (ROC) curve when optimizing an artificial neural network
(ANN), and tested whether it could improve classification performance. From an ongoing prospective study, we selected
a dataset of 174 cases for whom we have both REIS signals and diagnostic status verification. The dataset includes 66
"positive" cases recommended for biopsy due to detection of highly suspicious breast lesions and 108 "negative" cases
determined by imaging based examinations. A set of REIS-based feature differences, extracted from the two breasts
using a mirror-matched approach, was computed and constituted an initial feature pool. Using a leave-one-case-out
cross-validation method, we applied a genetic algorithm (GA) to train the ANN with an optimal subset of features. Two
optimization criteria were separately used in GA optimization, namely the area under the entire ROC curve (AUC) and
the partial area under the ROC curve, up to a predetermined threshold (i.e., 90% specificity). The results showed that
although the ANN optimized using the entire AUC yielded higher overall performance (AUC = 0.83 versus 0.76), the
ANN optimized using the partial ROC area criterion achieved substantially higher operational performance (i.e.,
increasing sensitivity level from 28% to 48% at 95% specificity and/ or from 48% to 58% at 90% specificity).
We have developed and preliminarily tested a new breast cancer risk prediction model based on computerized
bilateral mammographic tissue asymmetry. In this study, we investigated and compared the performance difference of
our risk prediction model when the bilateral mammographic tissue asymmetrical features were extracted in two different
methods namely (1) the entire breast area and (2) the mirror-matched local strips between the left and right breast. A
testing dataset including bilateral craniocaudal (CC) view images of 100 negative and 100 positive cases for developing
breast abnormalities or cancer was selected from a large and diverse full-field digital mammography (FFDM) image
database. To detect bilateral mammographic tissue asymmetry, a set of 20 initial "global" features were extracted from
the entire breast areas of two bilateral mammograms in CC view and their differences were computed. Meanwhile, a
pool of 16 local histogram-based statistic features was computed from eight mirror-matched strips between the left and
right breast. Using a genetic algorithm (GA) to select optimal features, two artificial neural networks (ANN) were built
to predict the risk of a test case developing cancer. Using the leave-one-case-out training and testing method, two GAoptimized
ANNs yielded the areas under receiver operating characteristic (ROC) curves of 0.754±0.024 (using feature
differences extracted from the entire breast area) and 0.726±0.026 (using the feature differences extracted from 8 pairs of
local strips), respectively. The risk prediction model using either ANN is able to detect 58.3% (35/60) of cancer cases 6
to 18 months earlier at 80% specificity level. This study compared two methods to compute bilateral mammographic
tissue asymmetry and demonstrated that bilateral mammographic tissue asymmetry was a useful breast cancer risk
indicator with high discriminatory power.
An interactive computer-aided detection or diagnosis (ICAD) scheme allows observers to query suspicious
abnormalities (lesions) depicted on medical images. Once a suspicious region is queried, ICAD segments the abnormal
region, computes a set of image features, searches for and identifies the reference regions depicted on the verified lesions
that are similar to the queried one. Based on the distribution of the selected similar regions, ICAD generates a detection
(or classification) score of the queried region depicting true-positive disease. In this study, we assessed the performance
and reliability of an ICAD scheme when using a database including total 1500 positive images depicted verified breast
masses and 1500 negative images depicted ICAD-cued false-positive regions as well as the leave-one-out testing method.
We conducted two experiments. In the first experiment, we tested the relationship between ICAD performance and the
size of reference database by systematically increasing the size of reference database from 200 to 3000 images. In the
second experiment, we tested the relationship between ICAD performance and the similarity level between the queried
image and the retrieved similar references by applying a set of thresholds to systematically remove the queried images
whose similarity level to their most "similar" reference images are lower than threshold. The performance was compared
based on the areas under ROC curves (AUC). The results showed that (1) as the increase of reference database, AUC
value monotonically increased from 0.636±0.041 to 0.854±0.004 and (2) as the increase of similarity threshold values,
AUC value also monotonically increased from 0.854±0.004 to 0.932±0.016. The increase of AUC values and the
decrease of their standard deviations indicate the improvement of both CAD performance and reliability. The study
suggested that (1) assembling the large and diverse reference databases and (2) assessing and reporting the reliability of
ICAD-generated results based on the similarity measurement are important in development and application of the ICAD
schemes.
The amplification status of human epidermal growth factor receptors 2 (HER2) genes is strongly associated
with clinical outcome in patients with breast cancer. The American Society of Clinical Oncology Tumor Marker
Guidelines Panel has recommended routine testing of HER2 status on all newly diagnosed metastatic breast cancers
since 2001. Although fluorescent in situ hybridization (FISH) technology provides superior accuracy as compared with
other approaches, current manual FISH analysis methods are somewhat subjective, tedious, and may introduce interreader
variability. The goal of this preliminary study is to develop and test a computer-aided detection (CAD) scheme to
assess HER2 status using FISH images. Forty FISH images were selected for this study from our genetic laboratory. The
CAD scheme first applies an adaptive, iterative threshold method followed by a labeling algorithm to segment cells of
possible interest. A set of classification rules is then used to identify analyzable interphase cells and discard nonanalyzable
cells due to cell overlapping and/or other image staining debris (or artifacts). The scheme then maps the
detected analyzable cells onto two other gray scale images corresponding to the red and green color of the original image
followed by application of a raster scan and labeling algorithms to separately detect the HER-2/neu ("red") and CEP17
("green") FISH signals. A simple distance based criterion is applied to detect and merge split FISH signals within each
cell. The CAD scheme computes the ratio between independent "red" and "green" FISH signals of all analyzable cells
identified on an image. If the ratio is ≥ 2.0, the FISH image is assumed to have been acquired from a HER2+ case;
otherwise, the FISH image is assumed to have been acquired from HER2- case. When we applied the CAD scheme to
the testing dataset, the average computed HER2 amplification ratios were 1.06±0.25 and 2.53±0.81 for HER2- and
HER2+ samples, respectively. The results show that the CAD scheme has the ability to automatically detect HER2 status
using FISH images. The success of CAD-guided FISH image analysis could result in a more objective, consistent, and
efficient approach in determining HER2 status of breast cancers.
Currently, breast cancer screening protocols are based on a woman's age, but not on other risk factors or on the physical
characteristics of her breasts. One commonly cited risk factor is dense breast tissue. This study is part of an effort to
provide basic information needed to develop automatically, individualized screening protocols, by clarifying the
relationships between age, risk, breast composition, lesion conspicuity, and other factors. In this project, a database was
established that includes 227 cancer negative cases and 116 cancer positive cases across a wide range of age groups. In
the cancer positive cases, we included a subgroup in which the cancer had been missed in the previous exam. Using our
physics based model of breast density, we quantified percentage of breast parenchyma as an index of density. Density
distributions and changes over time were analyzed. The most significant finding within this data was a significantly
slower density decrease over the time in the cancer positive group than in the cancer negative group, with no overall
difference in the density distribution in those two groups. False negative cases were found to be significantly more dense
than true positive cases. In addition, our results showed a trend of density decrease with increasing age, which is in
agreement with others' widely reported results.
KEYWORDS: Digital breast tomosynthesis, Computer aided design, Mammography, Computer aided diagnosis and therapy, Breast, Visualization, 3D image processing, Signal to noise ratio, Image filtering
Digital breast tomosynthesis (DBT) has emerged as a promising imaging modality for screening
mammography. However, visually detecting micro-calcification clusters depicted on DBT images is a difficult task.
Computer-aided detection (CAD) schemes for detecting micro-calcification clusters depicted on mammograms can
achieve high performance and the use of CAD results can assist radiologists in detecting subtle micro-calcification
clusters. In this study, we compared the performance of an available 2D based CAD scheme with one that includes a new
grouping and scoring method when applied to both projection and reconstructed DBT images. We selected a dataset
involving 96 DBT examinations acquired on 45 women. Each DBT image set included 11 low dose projection images
and a varying number of reconstructed image slices ranging from 18 to 87. In this dataset 20 true-positive micro-calcification
clusters were visually detected on the projection images and 40 were visually detected on the reconstructed
images, respectively. We first applied the CAD scheme that was previously developed in our laboratory to the DBT
dataset. We then tested a new grouping method that defines an independent cluster by grouping the same cluster detected
on different projection or reconstructed images. We then compared four scoring methods to assess the CAD
performance. The maximum sensitivity level observed for the different grouping and scoring methods were 70% and
88% for the projection and reconstructed images with a maximum false-positive rate of 4.0 and 15.9 per examination,
respectively. This preliminary study demonstrates that (1) among the maximum, the minimum or the average CAD
generated scores, using the maximum score of the grouped cluster regions achieved the highest performance level, (2)
the histogram based scoring method is reasonably effective in reducing false-positive detections on the projection images
but the overall CAD sensitivity is lower due to lower signal-to-noise ratio, and (3) CAD achieved higher sensitivity and higher false-positive rate (per examination) on the reconstructed images. We concluded that without changing the detection threshold or performing pre-filtering to possibly increase detection sensitivity, current CAD schemes developed and optimized for 2D mammograms perform relatively poorly and need to be re-optimized using DBT datasets and new grouping and scoring methods need to be incorporated into the schemes if these are to be used on the DBT examinations.
Xiao Hui Wang, Janet Durick, David Herbert, Amy Lu, Sarawathi Golla, Dilip Shinde, Samaia Piracha, Kristin Foley, Carl Fuhrman, Betty Shindel, J. Ken Leader, Walter Good
To improve radiologist's performance in lesion detection and diagnosis on 3D medical image dataset, we have conducted a pilot study to test viability and efficiency of the stereo display for lung nodule detection and classification. Using our previously developed stereo compositing methods, stereo image pairs were prestaged and precalculated from CT slices for real-time interactive display. Three display modes (i.e., stereoscopic 3D, orthogonal MIP and slice-by-slice) were compared for lung nodule detection and total of eight radiologists have participated this pilot study to interpret the images. The performance of lung nodule detection was analyzed and compared between the modes using FROC analysis. Subjective assessment indicates that stereo display was well accepted by the radiologists, despite some uncertainty of beneficial results due to the novelty of the display. The FROC analysis indicates a trend that, among the three display modes, stereo display resulted in the best performance of nodule detection followed by slice-based display, although no statistically significant difference was shown between the three modes. The stereo display of a stack of thin CT slices has the potential to clarify three-dimensional structures, while avoiding ambiguities due to tissue superposition. Few studies, however, have addressed actual utility of stereo display for medical diagnosis. Our preliminary results suggest a potential role of stereo display for improving radiologists' performance in medical detection and diagnosis, and also indicate some factors likely affect the performance with new display, such as novelty of the display, training effect from projected radiography interpretation and confidence with the new technology.
Many diagnostic problems involve the assessment of vascular structures or bronchial trees depicted in volumetric
datasets, but previous algorithms for segmenting cylindrical structures are not sufficiently robust for them to be widely
applied clinically. Local geometric information that is of importance in segmentation consists of voxel values and their
first and second derivatives. First derivatives can be generalized to the gradient and more generally the structure tensor,
while the second derivatives can be represented by Hessian matrices. It is desirable to exploit both kinds of information,
at the same time, in any voxel classification process, but few segmentation algorithms have attempted to do this. This
project compares segmentation based on the structure tensor to that based on the Hessian matrix, and attempts to
determine whether some combination of the two can demonstrate better performance than either individually. To
compare performance in a situation where a gold standard exists, the methods were tested on simulated tree structures.
We generated 3D tree structures with varying amounts of added noise, and processed them with algorithms based on the
structure tensor, the Hessian matrix, and a combination of the two. We applied an orientation-sensitive filter to smooth
the tensor fields. The results suggest that the structure tensor by itself is more effective in detecting cylindrical structures
than the Hessian tensor, and the combined tensor is better than either of the other tensors.
A workstation for testing the efficacy of stereographic displays for applications in radiology has been developed, and is currently being tested on lung CT exams acquired for lung cancer screening. The system exploits pre-staged rendering to achieve real-time dynamic display of slabs, where slab thickness, axial position, rendering method, brightness and contrast are interactively controlled by viewers. Stereo presentation is achieved by use of either frame-swapping images or cross-polarizing images. The system enables viewers to toggle between alternative renderings such as one using
distance-weighted ray casting by maximum-intensity-projection, which is optimal for detection of small features in many cases, and ray casting by distance-weighted averaging, for characterizing features once detected. A reporting mechanism is provided which allows viewers to use a stereo cursor to measure and mark the 3D locations of specific features of interest, after which a pop-up dialog box appears for entering findings. The system's impact on performance is being tested on chest CT exams for lung cancer screening. Radiologists' subjective assessments have been solicited for other
kinds of 3D exams (e.g., breast MRI) and their responses have been positive. Objective estimates of changes in performance and efficiency, however, must await the conclusion of our study.
Based on the need to increase the efficacy of chest CT for lung cancer screening, a stereoscopic display for viewing chest CT images has been developed. Stereo image pairs are generated from CT data by conventional stereo projection derived from a geometry that assumes the topmost slice being displayed is at the same distance as the screen of the physical display. Image grayscales are modified to make air transparent so that soft tissue structures of interest can be more easily seen. Because the process of combining multiple slices has a tendency to reduce the effective local contrast, we have included mechanisms to counteract this, such as linear and nonlinear local grayscale transforms. The physical display, which consists of a CRT viewed through shutter glasses, also provides for real-time adjustment of displayed thickness and axial position, as well as for changing brightness and contrast. While refinement of the stereo projection, contrast, and transparency models is ongoing, subjective evaluation of our current implementation indicates that the method has considerable potential for improving the efficiency of the detection of lung nodules. A more quantitative effort to assess its impact on performance, by ROC type methods, is underway.
The widespread adoption of chest CT for lung cancer screening will greatly increase the workload of chest radiologists. Contributing to this effort is the need for radiologists to differentiate between localized nodules and slices through linear structures such as blood vessels, in each of a large number of slices acquired for each subject. To increase efficiency and accuracy, thin slices can be combined to provide thicker slabs for presentation, but the resulting superposition of tissues can make it more difficult to detect and characterize smaller nodules. The stereo display of a stack of thin CT slices may be able to clarify three-dimensional structures, while avoiding the loss of resolution and ambiguities due to tissue superposition.
The current work focuses on the development and evaluation of stereo projection models that are appropriate for chest CT. As slices are combined into a three dimensional structure, maximum image intensity, which is limited by the display, must be preserved. But, compositing methods that effectively average slices together typically reduce contrast of subtle nodules. For monoscopic viewing, orthographic maximum-intensity projection (MIP), of thick slabs, has been employed to overcome this effect, but this method provides no information of depth or of the geometrical relationships between structures. Our comparison of various rendering options indicates that a stereographic perspective transformation, used in conjunction with a compositing model that combines maximum-intensity projection with an appropriate brightness weighting function, shows promise for this application. The main drawback uncovered was that, for the images used in this study, the lung volume was undersampled in the z-direction, resulting in certain unavoidable image artifacts.
Breast tissue density is one of the most cited risk factors in breast cancer development. Nevertheless, estimates of the magnitude of breast cancer risk associated with density vary substantially because of the inadequacy of methods used in tissue density assessment (e.g., subjective and/or qualitative assessment) and lack of a reliable gold standard. We have developed automated algorithms for quantitatively measuring breast composition from digitized mammograms. The results were compared to objective truth as determined by quantitative measures from breast MR images, as well as to subjective truth as determined by radiologists' readings from digitized mammograms using BI-RAD standards. Higher linear correlation between estimates calculated from mammograms using the methods developed herein and estimates derived from breast MR images demonstrates that the mammography-based methods will likely improve our ability to accurately determine the breast cancer risk associated with breast density. By using volumetric measures from breast MR images as a gold standard, we are able to estimate the adequacy and accuracy of our algorithms. The results can be used for providing a calibrated method for estimating breast composition from mammograms.
We investigated a new approach to improve the performance of a computer-aided detection (CAD) scheme in identifying masses depicted on images acquired earlier ("prior"). The scheme was trained using a dataset with simulated mass features. From a database with images acquired during two consecutive examinations, 100 locations matched pairs of malignant mass regions were selected in both the “current” and the most recent “prior” images. While reviewing the current images, mass regions were identified and as a result biopsies were ultimately performed. Prior images were not identified as suspicious by radiologists during the original interpretation. The same number of false-positive regions was also selected in both current and prior images. The selected regions were then randomly divided into training and testing datasets with 50 true-positive and 50 false-positive regions in each. For each selected region, five features; area, contrast, circularity, normalized standard deviation of radial length, and conspicuity; were computed. The ratios of the average difference of five feature values between current and prior mass regions in the training datasets were also computed. Multiplying these ratios by the computed values in current mass regions, we generated a new dataset of simulated features of “prior” mass regions. Three artificial neural networks (ANN) were trained. ANN-1 and ANN-2 were trained using training datasets of current and prior regions, respectively. ANN-3 was trained using simulated “prior” dataset. The performance of three ANNs was then evaluated using the testing dataset of prior images. Areas under ROC curves (Az) were 0.613 ± 0.026 for ANN-1, 0.678 ± 0.029 for ANN-2, and 0.667 ± 0.029 for ANN-3, respectively. This preliminary study demonstrated that one could estimate an average change of feature values over time and "adjust" CAD performance for better detection of masses at an earlier stage.
A novel technique for assessing local and global differences between mammographic images was developed. This method uses correlations between abstract features extracted from corresponding views to compare image properties without resorting to processes that depend on exact geometrical congruence, such as image subtraction, which have a tendency to produce excessive artifact. The method begins by normalizing both digitized mammograms, after which a series of global and local feature filters are applied to each image. Each filter calculates values characterizing a particular property of the given image, and these values, for each property of interest are arranged in a feature vector. Corresponding elements in the two feature vectors are combined to produce a difference vector that indicates the change in the particular properties between images. Features are selected which are expected to be relatively invariant with respect to breast compression.
KEYWORDS: 3D modeling, Magnetic resonance imaging, Breast, Image segmentation, Visualization, Tissues, Visual process modeling, Data modeling, 3D image processing, Tumor growth modeling
Contrast enhanced breast MRI is currently used as an adjuvant modality to x-ray mammography because of its ability to resolve ambiguities and determine the extent of malignancy. This study described techniques to create and visualize 3D geometric models of abnormal breast tissue. MRIs were performed on a General Electric 1.5 Tesla scanner using dual phased array breast coils. Image processing tasks included: 1) correction of image inhomogeneity caused by the coils, 2) segmentation of normal and abnormal tissue, and 3) modeling and visualization of the segmented tissue. The models were visualized using object-based surface rendering which revealed characteristics critical to differentiating benign from malignant tissue. Surface rendering illustrated the enhancement distribution and enhancement patterns. The modeling process condensed the multi-slice MRI data information and standardized its interpretation. Visualizing the 3D models should improve the radiologist's and/or surgeon's impression of the 3D shape, extent, and accessibility of the malignancy compared to viewing breast MRI data slice by slice.
The purpose was to evaluate the effect of incorporating negative but suspicious regions into a knowledge-based computer-aided detection (CAD) scheme of masses depicted in mammograms. To determine if a suspicious region is positive for a mass, the region was compared not only with actually positive regions (masses), but also with known negative regions. A set of quantitative measures (i.e., a positive, a negative, and a combined likelihood measure) was computed. In addition, a process was developed to integrate two likelihood measures that were derived using two selected features. An initial evaluation with 300 positive and 300 negative regions was performed to determine the parameters associated with the likelihood measures. Then, an independent set of 500 positive and 500 negative regions was used to test the performance of the CAD scheme. During the training phase, the performance was improved from Az=0.83 to 0.87 with the incorporation of negative regions and the integration process. During the independent test, the performance was improved from Az=0.80 to 0.83. The incorporation of negative regions and the integration process was found to add information to the scheme. Hence, it may offer a relatively robust solution to differentiate masses from normal tissue in mammograms.
In this study, we test a new method to automatically search for matched regions in bilateral digitized mammograms and to compute differences in region conspicuities in pairs of matched regions. One hundred pairs of bilateral images of the same view were selected for the experiment. Each pair of images depicted one verified mass. These 100 mass regions, along with 356 suspicious but actually negative mass regions, were first detected by a single-image-based CAD scheme. To find the matched regions in the corresponding bilateral images, a Procrustean-type technique was used to register the two images, which corrects the deformation of tissue structure between images by guaranteeing the registration of nipples, skin lines, and chest walls. Then, a region growth algorithm was applied to generate a growth region in the matched area, which has the same effective size as the suspicious region in the abnormal image. The conspicuities in the two matched regions, as well as their differences, were computed. Using the conspicuity in the original mass regions and the difference of conspicuities in the two matched regions as two identification indices to classify this set of 456 suspicious regions, the computed areas under the ROC curves (Az) were 0.77 and 0.75, respectively. This preliminary study indicates that by comparing the difference of conspicuities in two matched regions that a very useful feature for the CAD schemes can be extracted.
A novel figure-of-merit (FOM) for automatically quantifying the types of artifacts that appear in compressed images was investigated. This FOM is based on task specific linear combinations of magnitude, frequency and 'localized' structure information derived from difference images. For each elemental diagnostic task (e.g., detection of microcalcifications) a value is calculated as the weighted linear combination of the output of an array of filters, and the FOM is defined to be the maximum of these values, taken over all relevant diagnostic tasks. This FOM was tested by applying it to a previously assembled set of 60 mammograms that had been digitized and compressed at five different compression levels using our version of the original JPEG algorithm. The FOM results were compared to subjective assessments of image quality provided by nine radiologists. A subset consisting of 25 images was also processed with the JPEG 2000 algorithm and evaluated by the FOM. A significant correlation existed between readers' subjective ratings and FOMs for JPEG compressed images. A comparison between the results of the two compression algorithms reveals that, to achieve a comparable FOM level, the JPEG 2000 images were compressed at a bitrate that was typically 15% lower than that of images compressed with the original JPEG algorithm.
We present a simple algorithm for determining the fat fraction in magnetic resonance images of the breast. These computed values are intended to help train neural networks for determining breast composition from x-ray mammograms. The method relies on simple intensity thresholding to form a binary mask followed by morphological dilations and erosions, automated region selection and clustering the tissues within the mask into fat and parenchymal components. Correcting the image intensity nonuniformity due to the spatial sensitivity profile of the breast coil was found to be essential and easily accomplished with homologous filtering. In the absence of large artifacts, the algorithm was able to accurately calculate breast fat fractions.
In this paper, a novel method is used for computerized lesion detection and analysis in three-dimensional(3D) contrast enhanced MR breast images. The automatic analysis involves three steps: 1) alignment between series; 2) extraction of suspicious regions; and 3) application of feature classification to each region. Assuming that there are only small geometric deformations after global registration, we adopted a 3D thin-plate spline based registration method, in which the control points are determined using 3D gradient and local correlation. Experiments show superior correlation between neighboring slices with 3D alignment as compared to a previous two-dimensional(2D) method. After registration, a new series named enhancement rate images(ERIs) are created. Suspicious volumes-of-interest(VOIs) are identified by 3D region labeling after thresholding the ERIs. Since carcinomas can typically be characterized by irregular borders and rapid and high uptake of contrast followed by a washout, a set of morphological features(irregularity, spiculation index, etc) and enhancement features(small volume enhancement rate, slope of average rate, etc) are calculated for selected VOIs and evaluated in a rule-based classifier to identify malignant lesions from benign lesions or normal tissues.
The wide dynamic range present in digitized mammographic data, partially resulting from the non-uniform thickness of tissue during breast compression, makes it difficult to find window and level values that are appropriate to display the entire image. Further, this factor combined with the non- linearity of the relationship between density and log exposure, confound attempts to automatically derive tissue composition information directly from uncorrected data. This project attempts to address these issues by making appropriate local image corrections based on the characteristic curves of film and digitizer, as well as on the variations in tissue thickness during breast compression. Subjective comparisons of the display techniques developed in this project, to mammography displays based on local histogram equalization methods to reduce image dynamic range, clearly demonstrate superior performance of the methods presented in this paper. In addition to this subjective observation about image display, we also investigated the possibility of using corrected data to improve the performance of tissue composition measurements. A neural network classifier was developed to use features derived from the volume-corrected histogram of the corrected mammographic data to estimate tissue composition. Results indicate that tissue composition measurements are more highly correlated to radiologists' estimates, when they are derived from corrected images.
Registration of mammograms is frequently used in computer- aided-detection algorithms, and has been considered for use in the analysis of temporal sequences of screening exams. Previous image registration methods, employing affine transformations or Procrustean transforms based ona small number of fiducial points, have not proven to be entirely adequate. A significantly improved method to facilitate the display and analysis of temporal sequences of mammograms by optimizing image registration and grayscales, has been developed. This involves a fully automatic nonlinear geometric transformation, which puts corresponding skin lines, nipples and chest walls in registration and locally corrects pixel values based on the Jacobian of the transformation. Linear regression is applied between pairs of corresponding pixels after registration, and the derived regression equation is used to equalize grayscales. Although the geometric transformation is not able to correct interior tissue patterns for gross differences in the angle of view or differences resulting from skewing of the breast tissue parallel to the detector, sequences studied have been sufficiently consistent that typically only about 30 percent of images in a sequence are considered to be seriously incompatible with the remaining images. These methods clearly demonstrate a significant benefit for the display and analysis of sequences of digital mammograms.
The study is to investigate the use of a Bayesian belief network (BBN) in a computer-assisted diagnosis (CAD) scheme for mass detection in digitized mammograms. Two independent image sets were used in the experiments. After initial processing of image segmentation and adaptive topographic region growth in our CAD scheme, 288 true-positive mass regions and 2,204 false-positive regions were identified in the training image set. In the testing set, 304 true-positive and 1,586 false-positive regions were identified. Fifty features were computed for each region. After using a genetic algorithm search, a BBN was constructed based on 12 local and four global features in order to classify these regions as positive or negative for mass. The performance of the BBN was evaluated using an ROC methodology. The BBN achieved an area under the ROC curve of 0.873 plus or minus 0.009 in classifying the 304 positive and 1,586 negative regions in the testing set. This result was better than using an artificial neural network with the same set of input features. After incorporating the BBN into our CAD scheme as the last classification stage, we detected 80% of 189 positive mass cases (in 433 testing images) with an average detection rate of 0.76 false-positive regions per image. Therefore, this study demonstrated that a BBN approach could yield a comparable performance to that using other classifiers. Using a probabilistic learning concept and interpretable topology, the BBN provides a flexible approach to improving CAD schemes.
On mammograms, certain kinds of features related to masses (e.g., location, texture, degree of spiculation, and integrated density difference) tend to be relatively invariant, or at last predictable, with respect to breast compression. Thus, ipsilateral pairs of mammograms may contain information not available from analyzing single views separately. To demonstrate the feasibility of incorporating multi-view features into CAD algorithm, `single-image' CAD was applied to each individual image in a set of 60 ipsilateral studies, after which all possible pairs of suspicious regions, consisting of one from each view, were formed. For these 402 pairs we defined and evaluated `multi-view' features such as: (1) relative position of centers of regions; (2) ratio of lengths of region projections parallel to nipple axis lines; (3) ratio of integrated contrast difference; (4) ratio of the sizes of the suspicious regions; and (5) measure of relative complexity of region boundaries. Each pair was identified as either a `true positive/true positive' (T) pair (i.e., two regions which are projections of the same actual mass), or as a falsely associated pair (F). Distributions for each feature were calculated. A Bayesian network was trained and tested to classify pairs of suspicious regions based exclusively on the multi-view features described above. Distributions for all features were significantly difference for T versus F pairs as indicated by likelihood ratios. Performance of the Bayesian network, which was measured by ROC analysis, indicates a significant ability to distinguish between T pairs and F pairs (Az equals 0.82 +/- 0.03), using information that is attributed to the multi-view content. This study is the first demonstration that there is a significant amount of spatial information that can be derived from ipsilateral pairs of mammograms.
This project is a preliminary evaluation of two simple fully automatic nonlinear transformations which can map any mammographic image onto a reference image while guaranteeing registration of specific features. The first method automatically identifies skin lines, after which each pixel is given coordinates in the range [0,1] X [0,1], where the actual value of a coordinate is the fractional distance of the pixel between tissue boundaries in either the horizontal or vertical direction. This insures that skin lines are put in registration. The second method, which is the method of primary interest, automatically detects pectoral muscles, skin lines and nipple locations. For each image, a polar coordinate system is established with its origin at the intersection of the nipple axes line (NAL) and a line indicating the pectoral muscle. Points within a mammogram are identified by the angle of their position vector, relative to the NAL, and by their fractional distance between the origin and the skin line. This deforms mammograms in such a way that their pectoral lines, NALs and skin lines are all in registration. After images are deformed, their grayscales are adjusted by applying linear regression to pixel value pairs for corresponding tissue pixels. In a comparison of these methods to a previously reported 'translation/rotation' technique, evaluation of difference images clearly indicates that the polar coordinates method results in the most accurate registration of the transformations considered.
This study investigates the degree to which the performance of Bayesian belief networks (BBNs), for computer-assisted diagnosis of breast cancer, can be improved by optimizing their input feature sets using a genetic algorithm (GA). 421 cases (all women) were used in this study, of which 92 were positive for breast cancer. Each case contained both non-image information and image information derived from mammograms by radiologists. A GA was used to select an optimal subset of features, from a total of 21, to use as the basis for a BBN classifier. The figure-of-merit used in the GA's evaluation of feature subsets was Az, the area under the ROC curve produced by the corresponding BBN classifier. For each feature subset evaluated by the GA, a BBN was developed to classify positive and negative cases. Overall performance of the BBNs was evaluated using a jackknife testing method to calculate Az, for their respective ROC curves. The Az value of the BBN incorporating all 21 features was 0.851 plus or minus 0.012. After a 93 generation search, the GA found an optimal feature set with four non-image and four mammographic features, which achieved an Az value of 0.927 plus or minus 0.009. This study suggests that GAs are a viable means to optimize feature sets, and optimizing feature sets can result in significant performance improvements.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.