Matching Breast Masses Depicted on Different Views

Rationale and Objectives

Computerized determination of optimal search areas on mammograms for matching breast mass regions depicted on two ipsilateral views remains a challenge for developing multiview-based computer-aided detection (CAD) schemes. The purpose of this study was to compare three methods aimed at matching CAD-cued mass regions depicted on two views and the associated impact on CAD performance.

Materials and Methods

The three search methods used (1) an annular (fan-shaped) band, (2) a straight strip perpendicular to the estimated centerline, and (3) a mixed search area bound on the chest wall side by a straight line and an annular arc on the nipple side, respectively. An image database of 200 examinations with positive results depicting the masses on two views and 200 examinations with negative results was used for testing. Two performance assessment experiments were conducted. The first investigated the maximum matching sensitivity as a function of the search area size, and the second assessed the change in CAD performance using these three search methods.

Results

To include all 200 paired mass regions within the search areas, maximum widths were 28 and 68 mm for the use of the straight strip and the annular band search methods, respectively. When applying a single-image-based CAD scheme to this image database, 172 masses (86% sensitivity) and 523 false-positive (FP) regions (0.33 per image) were detected and cued. Among the positive findings, 92 were cued by the CAD system on both views, and 80 were cued on only one view. In an attempt to match as many of the 172 CAD-cued masses (true-positive [TP] regions) on two views by incrementally reducing the CAD threshold inside the different search areas, the CAD scheme generated 158 TP-TP paired matches with 14 TP-FP paired matches, 142 TP-TP paired matches with 30 TP-FP paired matches, and 146 TP-TP paired matches with 26 TP-FP paired matches, using the methods involving the straight strip, the annular band, and the mixed search areas, respectively. Using the straight strip search method, the CAD also eliminated 25% of FP regions initially cued by the single-image-based CAD scheme and generated the lowest case-based FP detection rate, namely, 15% less than that generated by the annular band method.

Conclusions

This study showed that among these three search methods, the straight strip method required a smaller search area and achieved the highest level of CAD performance.

Single-image-based computer-aided detection (CAD) systems for mammograms in which most subtle cancers are cued on only one view and are therefore more likely to be discarded by radiologists as false-positive (FP) cues may be limited in their ability to improve radiologists’ performance . Hence, a number of research groups (including ours) have been attempting to develop multiview-based CAD schemes that enable the incorporation of the related information regarding abnormalities depicted on two ipsilateral (ie, craniocaudal [CC] and mediolateral oblique [MLO]) views into the decision-making process of the schemes. Similarly, this information can also be used to improve CAD performance in terms of maximizing the number of paired depicted and cued masses.

The first step needed in these multiview-based CAD schemes is the matching (pairing) of detected suspicious regions depicting the same abnormality (ie, mass) on two views. For this purpose, the scheme must detect either one or two fiducial landmarks (eg, the nipple and/or the chest wall) to enable a “global” registration of the paired images in question by establishing a reference matching coordinates for both views. Once a suspicious mass region is detected on one view (a “queried region”), the scheme identifies a search area on the corresponding ipsilateral view and searches for a CAD-detected suspicious region within this area that is considered the “most similar” to the queried region. These two “matched” regions are defined as a “pair” of mass regions. Under the assumption that true-positive (TP) mass regions have a higher probability than FP detections to be correctly matched on two views , the resulting overall performance of multiview-based CAD schemes may improve by keeping (cuing) “correctly matched” suspicious mass regions depicted on two views while discarding all unmatched regions as FP identifications .

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Materials and methods

Testing Image Data Set

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The Three Search Methods

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Modification of the Straight Strip–Based Search Method

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Performance Assessment Experiments

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Results

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Table 1

Comparison of Mass Detection Performance Levels of the Single-Image-Based CAD Scheme and a Multiview-Based CAD Scheme When Using Each of the Three Search Methods

Multi-view based CAD scheme using different search method Variable Single-Image-Based CAD Scheme Straight Strip Search Method Annular Band Search Method Annular Band Search Method Mixed Search Method Minimum search area width (mm) N/A 28 28 68 20 CAD-cued masses 172 172 148 172 172 Case-based sensitivity 86% 86% 74% 86% 86% Masses cued on two views 92 158 137 142 146 Average no. of matching candidates N/A 1.67 1.62 2.73 2.33 CAD-cued FP regions 523 676 653 808 792 Cues discarded initially as FP regions N/A 131 142 62 76 No. of case-based FP cues 462 331 321 389 383 Case-based FP rate per image 0.29 0.21 0.20 0.24 0.24

CAD, computer-aided detection; FP, false-positive; N/A, not applicable.

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Discussion

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References

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Matching Breast Masses Depicted on Different Views

Rationale and Objectives

Materials and Methods

Results

Conclusions

Materials and methods

Testing Image Data Set

The Three Search Methods

Modification of the Straight Strip–Based Search Method

Performance Assessment Experiments

Results

Discussion

References

Further Reading

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