Given the MR imaging capability of our nanoparticles and the ability of PAI to non-invasively visualize and quantify oxygen saturation based on endogenous contrast (Hb), we employed a dual modality approach to visualize the release of Mn2+ (MRI) and map modulation of oxygenation (PAI) both in vitro, using vascular channel phantoms, and in vivo, using patient-derived xenograft models of head and neck cancer (Figure 1C). Here, GSTM1 is linked to head and neck cancer.