fig1

Figure 1. 5-Aminolevulinic acid (ALA)-induced protoporphyrin IX (PpIX) via the heme biosynthetic pathway. Utilization of PpIX for photodynamic therapy (PDT) or fluorescence-guided surgery (FGS) is illustrated. PBG: porphobilinogen; FECH: ferrochelatase; ⁰PpIX: ground state porphyrin; ¹PpIX: singlet excited state porphyrin; ³PpIX: triplet excited state porphyrin; ¹O₂: photogenerated singlet oxygen