Abstract: Objective: To investigate group-level changes in normalized iodine concentration (nIC) measured in active-tumor and whole-tumor regions using small-animal photon-counting detector CT (PCD-CT) at different growth time points of mouse triple-negative breast cancer (TNBC) and to evaluate the association of nIC with microvessel density (MVD) and vascular endothelial growth factor (VEGF). Methods: Fifty 4T1 mouse TNBC models were randomly assigned to five independent groups and underwent PCD-CT scanning and terminal pathological sampling on days 7, 14, 21, 28, and 35 after inoculation, constituting a multi-time-point cross-sectional design. nIC was normalized to abdominal aortic iodine concentration. Active-tumor region of interest (ROI) was used for the primary analysis, and whole-tumor ROI, including necrotic and liquefied regions, was added as a sensitivity analysis. Spearman correlation was used for time-point-specific analyses between nIC and MVD, Pearson correlation was used for the pooled analysis, and a linear model with time point as a categorical fixed effect was used for adjustment. Spearman correlation was used to assess the associations between nIC and VEGF in the pooled sample. Results: Mean tumor volume increased across successive time-point groups, whereas the apparent group-level growth rate estimated from the mean values of adjacent time-point groups decreased after day 21. Active-tumor nIC, whole-tumor nIC, MVD, and VEGF exhibited similar group-level rise-then-fall patterns across the time-point groups, with the highest values observed in the day-21 group. Active-tumor nIC exhibited a positive but nonsignificant correlation with MVD on day 7 (r_s=0.573, P=0.088) and moderate-to-strong correlations on days 14–35 (r_s=0.669–0.799, P＜0.05); the pooled Pearson correlation was r=0.844 (P＜0.001). After adjustment for time point, MVD remained positively associated with active-tumor nIC (B=0.000729, 95%CI=0.000474–0.000985, P＜0.001) and whole-tumor nIC (B=0.000666, 95%CI=0.000434–0.000898, P＜0.001). Unadjusted Spearman analyses exhibited positive correlations between VEGF expression and nIC values of both the active-tumor and whole-tumor regions.(r_s=0.467, P < 0.001 and r_s=0.536, P < 0.001, respectively). Central tumor necrosis was more pronounced in the day-28 and day-35 groups than in the earlier time-point groups. Conclusion: The nIC values of active-tumor and whole-tumor regionsexhibited a rise-then-fall pattern across the independent time-point groups and remained positively associated with MVD after adjustment for time point and with VEGF in the pooled analyses. These findings support the potential of small-animal PCD-CT nIC for noninvasive assessment of TNBC angiogenesis.