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Improved Differential Diagnosis of Breast Masses on Ultrasonographic Images with a Computer-Aided Diagnosis Scheme for Determining Histological Classifications

Objectives

A computer-aided diagnosis (CAD) scheme for determining histological classifications of breast masses is expected to be useful for clinicians in making a differential diagnosis. The purpose of this study was to evaluate the usefulness of using the CAD scheme on ultrasonographic images.

Methods

The database consisted of 390 breast ultrasonographic images with masses. Three experienced clinicians independently provided subjective ratings on the likelihood of malignancy for each of the 390 masses. Fifty benign masses (25 cysts and 25 fibroadenomas) and 50 malignant masses (25 noninvasive ductal carcinomas and 25 invasive ductal carcinomas) were selected as unknown cases for an observer study based on a stratified randomization method with the ratings. The likelihood of the histological classification in each unknown case was evaluated by the CAD scheme with image features that clinicians commonly use for describing masses. In the observer study, seven observers provided their confidence levels regarding the malignancy of the unknown case before and after viewing the likelihood of the histological classification. The usefulness of the CAD scheme was evaluated with a multireader multicase receiver operating characteristic (ROC) analysis.

Results

The areas under the ROC curves (AUCs) for all observers were improved by use of the CAD scheme. The average AUC increased from 0.716 without to 0.864 with the CAD scheme ( P = .006).

Conclusion

The presentation of the likelihood of the histological classification evaluated by the CAD scheme improved the clinicians’ performance and therefore would be useful in making a differential diagnosis of masses on ultrasonographic images.

Breast ultrasonography is thought to be more useful than mammography for detecting small breast cancers in dense breasts . However, introducing ultrasonography to breast cancer screening might result in a lower specificity and thereby increase the false positive rate . Tohno et al showed the rate of positive findings by ultrasonography to be 24%, and that it would decrease to 10% if simple cysts would be excluded from the positive findings . Therefore, ultrasonography may be able to achieve more effective breast cancer screening than mammography if clinicians can more accurately make a differential diagnosis on ultrasonographic images.

Computer-aided diagnosis (CAD) is one of the solutions for improving clinicians’ performance . CAD is a diagnostic method in which clinicians use the results analyzed by a computer as a “second opinion.” The usefulness of CAD at mammography has been shown on many studies. Jiang et al conducted observer studies for distinguishing between benign and malignant clustered microcalcifications with and without the computer output indicating the likelihood of malignancy. The average area under the receiver operating characteristic (ROC) curve (AUC) was thus found to increase from 0.61 to 0.75 by the computer aid ( P < .0001) . Timps et al showed the radiologists’ performances to improve significantly ( P < .05) when they used the computer output for the characterization of benign and malignant masses on mammograms using a temporal change analysis . Nakayama et al investigated the effect of presenting similar images on radiologists’ differential diagnosis of clustered microcalcifications on mammograms . The observer study found that the radiologists’ performance significantly increased with the use of similar images ( P = .0009).

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Materials and methods

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Case Selection

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Figure 1, Distribution of average confidence levels of malignancy by three clinicians. DCIS, ductal carcinoma in situ; FA, fibroadenomas; IDC, invasive ductal carcinoma.

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Observer Study

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Statistical Analysis

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Results

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Figure 2, Comparison of receiver operating characteristic (ROC) curves for the average performance of seven clinicians in differential diagnosis between benign and malignant masses on ultrasonographic images with computer-aided diagnosis (CAD) and without CAD. The average area under the ROC curve (AUC) was improved from 0.716 to 0.864 with CAD ( P = .006).

Table 1

AUCs for Clinicians in the Distinction between Benign and Malignant Masses with and without CAD

AUC Without CAD With CAD_P_ Expert A 0.787 0.853 .001 B 0.690 0.823 — C 0.733 0.765 .013Mean__0.7370.814.115 Surgeon D 0.625 0.955 — E 0.713 0.922 — F 0.728 0.861 .002 G 0.737 0.870 —Mean__0.7010.902.016 AllMean0.7160.874.002

Figure 3, Comparison of receiver operating characteristic (ROC) curves for the average performance of the expert group and the general group with and without computer-aided diagnosis (CAD). The average area under the ROC curve (AUC) for the general group was improved from 0.701 to 0.902 ( P = .016), whereas the average AUC for the expert group was improved from 0.737 to 0.814 ( P = .115).

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Figure 4, The average beneficial or detrimental changes in the confidence level resulting from the computer-aided diagnosis scheme. The computer output was assumed to have a beneficial or detrimental effect on an observer's diagnosis when the difference was greater than 0.1.

Table 2

Number of Cases in Which CAD had a Beneficial or Detrimental Effect

Beneficially Detrimentally Expert A 17 0 B 25 2 C 5 1Mean__4__2 Surgeon D 65 8 E 64 2 F 32 1 G 26 1Mean__66__3AllMean472

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Discussion

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Figure 5, A case in which the average confidence level changed most beneficially. The average confidence level for this case with invasive ductal carcinoma changed from 0.289 without computer-aided diagnosis (CAD) to 0.547 with CAD.

Figure 6, Two cases of noninvasive ductal carcinomas in which the average confidence levels changed detrimentally with computer-aided diagnosis. The average confidence level for the case in (a) changed from 0.422 to 0.290, whereas that in (b) changed from 0.640 to 0.510.

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Conclusion

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Appendix

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References

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