http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2929432/ It is generally believed that phagocytes in healthy tissues rapidly and efficiently remove PS expressing cells and cell remnants. Diseased tissues on the other hand have a sustained presence of cell surface expressed PS as a result of an imbalance in appearance and clearance of PS expressing cells and cell remnants. Cell surface expressed PS is therefore a useful target for Molecular Imaging and Targeted Drug Delivery (TDD) strategies.