This work proposes a new method of building 3D models of microcalcification clusters and describes the validation of their realistic appearance when simulated into 2D digital mammograms and into breast tomosynthesisimages.Methods:
A micro-CT unit was used to scan 23 breast biopsy specimens of microcalcification clusters with malignant and benign characteristics and their 3D reconstructed datasets were segmented to obtain 3D models of microcalcification clusters. These models were then adjusted for the x-ray spectrum used and for the system resolution and simulated into 2D projection images to obtain mammograms after image processing and into tomographic sequences of projection images, which were then reconstructed to form 3D tomosynthesis datasets. Six radiologists were asked to distinguish between 40 real and 40 simulated clusters of microcalcifications in two separate studies on 2D mammography and tomosynthesis datasets. Receiver operating characteristic (ROC) analysis was used to test the ability of each observer to distinguish between simulated and real microcalcification clusters. The kappa statistic was applied to assess how often the individual simulated and real microcalcification clusters had received similar scores (“agreement”) on their realistic appearance in both modalities. This analysis was performed for all readers and for the real and the simulated group of microcalcification clusters separately. “Poor” agreement would reflect radiologists’ confusion between simulated and real clusters, i.e., lesions not systematically evaluated in both modalities as either simulated or real, and would therefore be interpreted as a success of the present models.Results:
The area under the ROC curve, averaged over the observers, was 0.55 (95% confidence interval [0.44, 0.66]) for the 2D study, and 0.46 (95% confidence interval [0.29, 0.64]) for the tomosynthesis study, indicating no statistically significant difference between real and simulated lesions (p > 0.05). Agreement between allocated lesion scores for 2D mammography and those for the tomosynthesis series was poor.Conclusions:
The realistic appearance of the 3D models of microcalcification clusters, whether malignant or benign clusters, was confirmed for 2D digital mammographyimages and the breast tomosynthesis datasets; this database of clusters is suitable for use in future observer performance studies related to the detectability of microcalcification clusters. Such studies include comparing 2D digital mammography to breast tomosynthesis and comparing different reconstruction algorithms.
This work is part of the OPTIMAM project which is funded by CR-UK & EPSRC Cancer Imaging Program in Surrey, in association with the MRC and Department of Health (England). The authors are grateful to the radiologists, who participated in the studies: Dr. Andreas Van Steen, Dr. Sandra Postema, Dr. Kirsten Joossens, Dr. Ilse Vervloessem, and Dr. Riet D’Hauwe. The authors would like to thank Thomas Mertelmeier from Siemens (Erlangen, Germany) for providing the reconstruction software “TomoEngine” and the reprocessing software “OpView2.”
II. MATERIALS AND METHODS
II.A. Simulation of 3D models of microcalcification
II.A.1. 3D model of microcalcification cluster
II.A.2. Initial sets of microcalcification clusters
II.B. Simulation framework
II.B.1. System specifications
II.B.2. Ideal template generation
II.B.3. Template modification for MTF
II.B.4. Template modification for noise
II.B.5. Insertion and reconstruction/processing
II.C. Validation of the simulation
II.C.1. Image datasets
II.C.2. Observer study
II.C.3. Statistical analysis
III.A. Results of the 2D FFDM study
III.B. Results of the tomosynthesis study
III.Cxs. Comparison between 2D FFDM and breast tomosynthesis
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