In this work, we conducted an imaging study to make a direct, quantitative comparison of image features measured by
film and full-field digital mammography (FFDM). We acquired images of cadaver breast specimens containing
simulated microcalcifications using both a GE digital mammography system and a screen-film system. To quantify the
image features, we calculated and compared a set of 12 texture features derived from spatial gray-level dependence
matrices. Our results demonstrate that there is a great degree of agreement between film and FFDM, with the correlation
coefficient of the feature vector (formed by the 12 textural features) being 0.9569 between the two; in addition, a paired
sign test reveals no significant difference between film and FFDM features. These results indicate that textural features
may be interchangeable between film and FFDM for CAD algorithms.
The ultimate goal of this project is to investigate whether the effect of a computer-aided detection (CAD) system on
readers' performance (especially, in situation of an upgrade of the CAD system, or between two different CAD systems
with similar design) can be accurately predicted without having to perform a multi-reader multi-case (MRMC) observer
study and, if such prediction is possible, to establish the underlying methodology. Our current study is intended to
provide evidence that would substantiate efforts toward such investigation. The objectives of this study were 1) to
investigate the relationship between the number of radiologists reading a dataset of thoracic computed tomography (CT)
images to identify lung nodules and the number of distinct findings and 2) to determine the number of readers needed to
identify almost all clinically distinct findings in a dataset. We used data from a multi-reader multi-case (MRMC)
observer study that consisted of six radiologists interpreting 85 thoracic CT examinations. To further illustrate our
approach, we also utilized simulated data consisting of twelve readers interpreting 198 samples equally distributed
between three levels of detection difficulty. For each possible reader grouping, the number of distinct findings identified
by the readers in the group was calculated. Five types of regression models used to describe the relationship between the
average number of distinct findings per case and the number of readers needed were compared. The result showed that
the logistic model best fitted both the thoracic CT data and the simulated data. Our assumption is that adding more
readers after a certain reader set size would mostly add redundant findings and, therefore, the benefit would be
negligible. Using this model, the predicted number of readers was found to depend on the type of findings considered.
Our study showed that the number of clinically distinct findings that can be identified by radiologists on CT lung
examinations without the use of a CAD system may be limited and that identifying almost all of these findings may only
require a limited number of readers.
KEYWORDS: Computer aided diagnosis and therapy, Signal detection, Signal to noise ratio, Image quality, Mammography, Imaging systems, Image segmentation, Digital mammography, Sensors, Bone
Most computer-aided detection (CADe) schemes were developed for digitized screen-film mammography (dSFM) and
are being transitioned to full-field digital mammography (FFDM). In this research, phantoms were used to relate image
quality differences to the performance of the multiple components of our microcalcification CADe scheme, and to
identify to what extent, if any, each CADe component is likely to require modification for FFDM. We compared
multiple image quality metrics for a dSFM imaging chain (GE DMR, MinR-2000 and Lumisiys digitizer) and an FFDM
system (GE Senographe 2000D) and related them to CADe performance for images of 1) contrast-detail phantom disks
and 2) microcalcification phantoms (bone fragments and cadaver breasts). Higher object signal-to noise ratio (SNR) in
FFDM compared with dSFM (p<0.05 for 62% of disks, and p>0.05 for 32% of disks) led to superior CADe signal and
cluster detection FROC performance. Signal segmentation was comparable (p>0.05 for 74% of disks) in dSFM and
FFDM and superior in FFDM (p<0.05) for 19% of disks. Better FFDM temporal stability led to more reproducible
CADe performance. For microcalcification phantoms, seven of eight computer-calculated features performed better or
comparably (p<0.05) at classifying true- and false-positive detections in FFDM. In conclusion, the image quality
improvements offered by FFDM compared to dSFM led to comparable or improved performance of the multiple stages
of our CADe scheme for microcalcification detection.
We are investigating the use of special mammographic views, i.e. magnification and spot compression views, into computerized classification schemes for malignant versus benign microcalcification clusters. Radiologists often recall patients with suspicious lesions for additional views. We expect that the fusion, or combination, of information extracted from special views and conventional mammograms will improve the performances of computer-aided diagnosis (CAD) schemes for classification of malignant versus benign microcalcification clusters. It has been shown that reading with CAD improves radiologists' performances. The CAD scheme is applied separately to conventional mammograms and special views. The scheme consists of segmentation of manually-identified microcalcifications, followed by extraction of microcalcification-based geometrical and textural features in addition to cluster-based features. Linear discriminant analysis (LDA) is then applied to each image to classify a cluster as malignant or benign. The leave-one-out technique is used for training and testing the classifier. The resulting likelihoods of malignancy output from the LDA applied separately to the conventional mammograms and special views are combined using the maximum classifier output. We applied the proposed technique to a database of 75 biopsy-proven patients (31 malignant and 44 benign). The case-based performances for classification of malignant versus benign microcalcification clusters resulted in an area under the receiver operating characteristic (ROC) curves, Az, of: 0.771 on conventional mammograms, 0.845 on special views, and 0.908 when merging likelihoods of malignancy from conventional mammograms and special views. These preliminary results indicate that the proposed technique of combining information from special views with that from conventional mammograms can improve computerized classification of microcalcification clusters.
There is now a large effort towards developing computer- aided diagnosis (CAD) techniques. It is important to be able to compare performance of different approaches to be able to determine which ones are the most efficacious. There are currently a number of barriers preventing meaningful (statistical) comparisons, two of which are discussed in this paper: database composition and scoring protocol. We have examined how the choice of cases used to test a CAD scheme can affect its performance. We found that our computer scheme varied between a sensitivity of 100% to 77%, at a false-positive rate of 1.0 per image, with only 100% change in the composition of the database. To evaluate the performance of a CAD scheme the output of the computer must be graded. There are a number of different criteria that are being used by different investigators. We have found that for the same set of detection results, the measured sensitivity can be between 40 - 90% depending on the scoring methodology. Clearly consensus must be reached on these two issues in order for the field to make rapid progress. As it stands now, it is not possible to make meaningful comparisons of different techniques.
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