Comparison of early and delayed quantified indices of double-phase 99mTc MIBI scintimammography in the detection of primary breast cancer

Purpose: To compare the diagnostic accuracy and incremental diagnostic role of quantitative indices of early and delayed lesion to non-lesion ratios (L/Ns) in the detection of primary breast cancer. Material and Methods: Double-phase 99m Tc MIBI scintimammography (SMM) (early 10 min, delayed 3 h) was performed after injection of 750 MBq of 99m Tc MIBI in 446 highly suspected breast cancer patients (malignant: 311, benign: 135). For visual analysis, five scoring methods were used, and, for quantitative analysis, early and delayed L/Ns were calculated. Receiver operating characteristic curve (ROC) analyses were performed to determine the optimal visual grade, and to calculate cut-off values of quantitative indices for differentiation of malignant and benign diseases and to investigate whether the quantitative indices could provide incremental diagnostic values in addition to visual analysis. Results: Optimal visual grades were above 4 and 5 in the detection of breast cancer. Sensitivity was 84.2% and specificity 79.3%; the area under the curve (AUC) was 0.832 (95% CI, 0.794-0.866) and standard error was 0.019. Early and delayed L/Ns of malignant breast disease were significantly higher than those of benign disease (early: 2.01±0.99 versus 1.13±0.26 (P<0.001); delayed: 1.68±0.69 versus 1.11±0.23 (P<0.001)). The optimal L/Ns for the detection of primary breast cancer were 1.27 for early and 1.12 for delayed imaging. When early L/N 1.27 was used as cut-off value for the detection of primary breast cancer, the sensitivity of SMM was 77.8% and specificity 85.2%. The AUC was 0.856 (95% CI, 0.820-0.888). When delayed L/N 1.12 was used, sensitivity and specificity were 81.4% and 78.5%, respectively. The AUC was 0.834 (95% CI, 0.796-0.867). The ROC comparison of early and delayed L/N showed no statistical difference in the detection of malignant breast disease (P=0.403). When the delayed L/N was added to the early one, early plus delayed quantitative analysis (E+D) showed 86.5% sensitivity and 74.8% specificity. However, the AUCs of E+D (0.854, 95% CI, 0.767-0.842) and early L/N (E) (0.856) showed no statistical difference (P=0.614). When grades 4 and 5 were used as cut-off visual grade, sensitivity and specificity were 84.2% and 79.3%, respectively. When the E was added to visual grade, visual plus early L/N (V+E) showed 89.4% sensitivity and 77% specificity. The AUC of V+E (0.867, 95% CI, 0.832-0.897) was significantly higher than that of visual analysis (V) (0.832, 95% CI, 0.794-0.866, P<0.001). When the delayed L/N (D) was added to visual grade, visual plus delayed L/N (V+D) showed 89.4% sensitivity and 74.1% specificity. The AUCs of V+D (0.852, 95% CI, 0.816-0.884) and V revealed no statistical differences (P=0.052). Conclusion: From this study, the optimal visual grades for diagnosis of breast cancer were grades 4 and 5; the cut-off values of L/Ns were 1.27 for early and 1.12 for delayed imaging. It was also found that early L/Ns provide incremental value in addition to visual analysis. However, delayed L/N revealed no incremental value. Therefore, the delayed image should not be routinely performed for purposes of primary breast cancer detection.