By the end of this trajectory, mean signal changes of 13.1% ± 1.9% and 0.7% ± 1.5% were observed in the presence of test and control xenografts, respectively, a significant difference (t-test p=0.007, n = 3) that indicates that FAP-expressing cancer cells are selectively and robustly detected by the FAPVap sensor in vivo (Figure 2C). Here, FAP is linked to cancer.