The reduction of false positive marks in breast mass CAD is an active area of research. Typically, the problem
can be approached either by developing more discriminative features or by employing different classifier designs.
Usually one intends to find an optimal combination of classifier configuration and small number of features to
ensure high classification performance and a robust model with good generalization capabilities.
In this paper, we investigate the potential benefit of relying on a support vector machine (SVM) classifier
for the detection of masses. The evaluation is based on a 10-fold cross validation over a large database of screen
film mammograms (10397 images). The purpose of this study is twofold: first, we assess the SVM performance
compared to neural networks (NNet), k-nearest neighbor classification (k-NN) and linear discriminant analysis
(LDA). Second, we study the classifiers' performances when using a set of 30 and a set of 73 region-based
features. The CAD performance is quantified by the mean sensitivity in 0.05 to 1 false positives per exam on
the free-response receiver operating characteristic curve.
The best mean exam sensitivities found were 0.545, 0.636, 0.648, 0.675 for LDA, k-NN, NNet and SVM.
K-NN and NNet proved to be stable against variation of the featuresets. Conversely, LDA and SVM exhibited
an increase in performance when adding more features. It is concluded that with an SVM a more pronounced
reduction of false positives is possible, given that a large number of cases and features are available.
Background. Contrary to what may be expected, finding abnormalities in complex images like pulmonary
nodules in chest radiographs is not dominated by time-consuming search strategies but by an almost immediate
global interpretation. This was already known in the nineteen-seventies from experiments with briefly flashed
chest radiographs. Later on, experiments with eye-trackers showed that abnormalities attracted the attention
quite fast but often without further reader actions. Prolonging one's search seldom leads to newly found abnormalities
and may even increase the chance of errors. The problem of reading chest radiographs is therefore
not dominated by finding the abnormalities, but by interpreting them. Hypothesis. This suggests that readers
could benefit from computer-aided detection (CAD) systems not so much by their ability to prompt potential
abnormalities, but more from their ability to 'interpret' the potential abnormalities. In this paper, this hypothesis
was investigated by an observer experiment. Experiment. In one condition, the traditional CAD condition,
the most suspicious CAD locations were shown to the subjects, without telling them the levels of suspiciousness
according to CAD. In the other condition, interactive CAD condition, levels of suspiciousness were given,
but only when readers requested them at specified locations. These two conditions focus on decreasing search
errors and decision errors, respectively. Results of reading without CAD were also recorded. Six subjects, all
non-radiologists, read 223 chest radiographs in both conditions. CAD results were obtained from the OnGuard
5.0 system developed by Riverain Medical (Miamisburg, Ohio). Results. The observer data were analyzed by
Location Response Operating Characteristic analysis (LROC). It was found that: 1) With the aid of CAD, the
performance is significantly better than without CAD; 2) The performance with interactive CAD is significantly
better than with traditional CAD at low false positive rates.
KEYWORDS: Computer aided diagnosis and therapy, Mammography, Computer aided design, CAD systems, Cancer, Computing systems, Detection and tracking algorithms, Visualization, Visual process modeling, Breast cancer
Most computer aided detection (CAD) systems for mammographic mass detection display all suspicious regions
identified by computer algorithms and are mainly intended to avoid missing cancers due to perceptual oversights.
Considering that interpretation failure is recognized to be a more common cause of missing cancers in screening
than perceptual oversights, a dedicated mammographic CAD system has been developed that can be queried
interactively for the presence of CAD prompts using a mouse click. To assess the potential benefit of using CAD
in an interactive way, an observer study was conducted in which 4 radiologists and 6 non-radiologists evaluated
60 cases with and without CAD, to compare the detection performance of the unaided reader with that of the
reader with CAD assistance. 20 cases had a malignant mass, and 40 were cancer-free. During the reading sessions
we recorded time and probed locations which reveal information about the search strategy and detection process.
The purpose of this study is to determine a relation between detection performance and time to first probe of
the lesion and to investigate if longer reading times lead to more reports of malignant lesions in lesion-free areas.
On average, 65.0% of the malignant lesions were found within 60 seconds and this percentage stabilizes after this
period. Results suggest that longer reading time did not lead to more false positives. 74.6% of the reported true
positive findings were hit by the first probe, and 93.2% were hit within 5 probes, which may suggest that many
of the correctly reported malignant masses were perceived immediately after image onset.
Most of the current CAD systems detect suspicious mass regions independently in single views. In this paper
we present a method to match corresponding regions in mediolateral oblique (MLO) and craniocaudal (CC)
mammographic views of the breast. For every possible combination of mass regions in the MLO view and CC
view, a number of features are computed, such as the difference in distance of a region to the nipple, a texture
similarity measure, the gray scale correlation and the likelihood of malignancy of both regions computed by single-view
analysis. In previous research, Linear Discriminant Analysis was used to discriminate between correct and
incorrect links. In this paper we investigate if the performance can be improved by employing a statistical method
in which four classes are distinguished. These four classes are defined by the combinations of view (MLO/CC)
and pathology (TP/FP) labels. We use distance-weighted k-Nearest Neighbor density estimation to estimate the
likelihood of a region combination. Next, a correspondence score is calculated as the likelihood that the region
combination is a TP-TP link. The method was tested on 412 cases with a malignant lesion visible in at least
one of the views. In 82.4% of the cases a correct link could be established between the TP detections in both
views. In future work, we will use the framework presented here to develop a context dependent region matching
scheme, which takes the number and likelihood of possible alternatives into account. It is expected that more
accurate determination of matching probabilities will lead to improved CAD performance.
In this paper, we compare two state-of-the-art classification techniques characterizing masses as either benign
or malignant, using a dataset consisting of 271 cases (131 benign and 140 malignant), containing both a MLO
and CC view. For suspect regions in a digitized mammogram, 12 out of 81 calculated image features have been
selected for investigating the classification accuracy of support vector machines (SVMs) and Bayesian networks
(BNs). Additional techniques for improving their performance were included in their comparison: the Manly
transformation for achieving a normal distribution of image features and principal component analysis (PCA) for
reducing our high-dimensional data. The performance of the classifiers were evaluated with Receiver Operating
Characteristics (ROC) analysis. The classifiers were trained and tested using a k-fold cross-validation test method
(k=10). It was found that the area under the ROC curve (Az) of the BN increased significantly (p=0.0002)
using the Manly transformation, from Az = 0.767 to Az = 0.795. The Manly transformation did not result in
a significant change for SVMs. Also the difference between SVMs and BNs using the transformed dataset was
not statistically significant (p=0.78). Applying PCA resulted in an improvement in classification accuracy of the
naive Bayesian classifier, from Az = 0.767 to Az = 0.786. The difference in classification performance between
BNs and SVMs after applying PCA was small and not statistically significant (p=0.11).
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