CASP3 and neoplasm: This low required dose can be attributed to the caspase-3-triggered in situ nanoaggregation and MR signal amplification strategies for identifying tumor death, since neither the non-cyclizable control (NC-ctrl, Figs 3 and 4) nor a small molecule MRI contrast agent ProHance® (Supplementary Fig. S3) was able to identify the response to therapy.