Figure 1.

Schematic representation of PDT mechanism and list of ultrasound (US) and photoacoustic imaging surrogate markers obtained pre‐, during and post‐therapy. The photosensitizer (PS) is a phototoxic theranostic agent that upon light activation transitions into an excited triplet state and reacts with the surrounding environment (such as ground state molecular oxygen) to generate cytotoxic reactive species (such as singlet oxygen) leading to cell death. The bottom panel lists various structural and functional information that can be obtained with US and photoacoustic imaging to guide, monitor and assess PDT response. StO₂, blood oxygen saturation. pO₂, partial pressure of oxygen.