CD68 and infection: Importantly, both the 19F-positive area (Fig. 3E; r = 0.882, p = 0.004) as well as the CD68-positive area (Fig. 3F; r = 0.720, p = 0.044) in tumor sections of VACV-treated animals positively correlated with the degree of VACV-infection as determined by the GFP-positive tumor area enabling indirect intratumoral virus detection.