Multilevel learning-based segmentation of ill-defined and spiculated masses in mammograms
Flowchart of the proposed MLS technique. Major processes of the method as shown in rounded rectangles include pixel-level soft segmentation, object-level detection, and spiculation detection.
The distribution of the mass statistics of shape, margin, density, sizes, and subtlety ranking within the database.
Flowchart of ISLM. For the training process, regional features of training subpatches are used for the pixel-level mass/nonmass classifier learning. For the testing process, the learned classifier is used to generate a mass possibility map for the whole testing image. A high intensity value in the mass probability map represents a high likelihood to be mass tissue. It is seen that very high intensity covers mass body and most of mass boundary with edge.
Results from the pixel-level classification. (a) The original ROI, (b) the mass probability map produced by the two-phase pixel-level classifiers, (c) the segmentation ground truth generated from multiple radiologists (with majority of five radiologists’ consensus), and (d) the ground truth contour superimposed on the original ROI.
Example of spiculation detection on a synthetic image. (a) Synthetic linear structures superimposed on a fatty mammographic background, (b) the ridge detector response, (c) the extracted backbone of the spiculation, and (d) the superimposed backbone on the original image.
Results of multiscale spiculation detection, (a) The original ROI, (b) the multiscale line-strength image, (c) the detected spicules, (d) the detected spicules superimposed on the ROI, and (e) the final spiculation map.
Example outputs of the multiphase pixel-level classification. (a) The original ROI, (b) the PM generated by the first phase classifier, (c) the PM generated by the two-phase classifiers, and (d) the ground truth provided by the radiologists. Note that the noisy responses on the upper left corner of (b) and (c) come from the pectoral muscles, which have been clearly suppressed by the two-phase classifier with low classification values produced.
The box and whisker plots of the distribution of the segmentation measurements. (a) Box plots of AOR, (b) box plots of AMINDIST, and (c) box plots of HSDIST. The vertical lines of the boxes correspond to the lower, median, and upper quartile. Each cross represents an outlier. The vertical dashed line in (a) corresponds to the threshold for a good segmentation with , which is adopted in the literature (Ref. 8).
Segmentation results. From left to right, they are the original ROI, segmentation result of MLFA, LS, MLS, manual segmentation, and the contours superimposed on the original image of the MLS approach (white contour) and radiologists’ manual segmentation (black contour). The BI-RADS descriptors of a mass in margin and shape are also shown under each original image in the first column.
The WIs with CI at 0.95 for the three segmentation measurements of the algorithm and the radiologists. (a) WI of AOR, (b) WI of AMINDIST, and (c) WI of HSDIST.
Margin segmentation performance. (a) The box and whisker plots of the distribution of MAOR, (b) WI of MAOR for the algorithm and the radiologists. The vertical dashed line in (a) corresponds to the threshold for a good margin segmentation with , which is determined in this study by considering the difficulty in segmenting the margin portion.
Illustration of cases with considerable disagreement between the computer segmentation and the ground truth. (a) A segmentation of is obtained on a low contrast mammogram. (b) A segmentation case with falsely included ducts as spiculations. The contours superimposed on the original image are the MLS approach (white contour) and manual segmentation (black contour).
Measurements of segmentation accuracy with the three proposed methods. Note that AMINDIST and HSDIST are distance based measurements. The high distance value means low similarity between computer segmentation and radiologists’ delineation. The reciprocal of the distance value is used as the segmentation similarity measurement for testing the multiobserver agreement in Sec. III C.
MAOR for various methods.
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