FRI approaches were first described in 1999 [44] and then successfully used to study epidermal growth factor receptor (EGFR) labeled with Cy5.5 in breast tumors [45], tumor protease activity of breast carcinoma [44,46], protease activity in arthritis [47], osteoblast activity in vertebra [48] and GFP expressing tumors [49] in mice. Here, EGFR is linked to breast carcinoma.