Patent ID: 7473415

Claim:
A method of fluorescence imaging, comprising introducing a near infrared fluorescent contrast agent comprising a compound of the formula below or a pharmaceutically acceptable salt thereof into a living body, exposing said body to an excitation light, and detecting near infrared fluorescence from the contrast agent wherein R 1 , R 2 , R 7 , and R 8 independently represent a substituted or unsubstituted C 1 -C 10 alkyl group or a substituted or unsubstituted aryl group; or R 1 R 2 and/or R 7 and R 8 bind to each other to form a ring; R 3 , R 4 , R 5 , R 6 , R 9 , R 10 , R 11 and R 12 independently represent a hydrogen atom, a substituted or unsubstituted C 1 -C 6 alkyl group, a substituted or unsubstituted aryl group, a substituted or unsubstituted heteroaryl group, a halogen atom, cyano group, carboxyl group, or sulfo group; or two of R 3 , R 4 , R 5 , R 6 , R 9 , R 10 , R 11 and R 12 bind to each other to form a ring; X 2 represent a substituted or unsubstituted C 1 -C 15 alkyl group or a substituted or unsubstituted aryl group; X 1 is a group represented by the following formula wherein X 1 and X 2 in total have 2 or 4 carboxyl groups; Y 1 and Y 2 independently represent a substituted or unsubstituted divalent linking group; m 1 represents 0 or 1; m 2 represents 0 or 1; m 3 represents 0 or 1; L 1 , L 2 , L 3 , L 4 , L 5 , L 6 , and L 7 independently represent a substituted or unsubstituted methine group, provided that when two or more of the methine groups have substituents, the substituents bind to each other to form a ring; M represents a hydrogen atom, a metal, or a quaternary ammonium salt; and n represents an integer of 1 to 7 necessary for neutralizing charge.