A method of imaging arthritis in a subject, comprising administering to the subject a tracer which comprises a peptide conjugated to a radionuclide, and imaging the subject by 2D nuclear imaging or by 3D detection of single-photon emission events, characterized in that the peptide is a compound of Formula wherein: - R represents arginine or N-methyl arginine; - G represents glycine; - D represents aspartic acid; - Y 1 is an amino acid residue selected from aspartic acid, glutamic acid, asparagine, glutamine, lysine and arginine wherein the side-chain of Y 1 is bonded via a heteroatom in the side-chain to the moiety -L-Z; - The moieties -Y 2 -S- and -Y 3 -S- each independently represent an amino acid residue capable of forming a disulphide bond -Y 2 -S-S-Y 3 -; - Y 4 is an amino acid residue selected from valine, leucine, isoleucine, methionine, phenylalanine, tyrosine and tryptophan; - The moiety -Y 5 -(CH 2) p -S- represents a sulphur-containing amino acid residue; wherein p is 1 or 2; - R 1 represents -(CH 2) q -(Ar) r -(CH 2) s -, wherein q and s are each independently 0 or an integer, wherein q + s is an integer from 1 to 8, and wherein r is 0 or 1; and wherein Ar is a C 6 arylene group; - R 2 is absent or represents -Het-((CH 2) n Het) m R b HetR a; - n is 1 or 2; - m is an integer from 1 to 6; - each Het is independently -O- or -NR a -; - R b is absent or is C 1 to C 6 alkylene which may be optionally substituted by from 1 to 3 oxo groups and/or may be interrupted by from 1 to 3 groups selected from -O- and -C -; - each R a is independently selected from H and C 1 to C 2 alkyl; - L is -C -(C 1 -C 6 alkylene)-C -; wherein the alkylene group of L may be optionally interrupted by -O- and/or wherein the alkylene group of L is unsubstituted or substituted by 1 or 2 substituents selected from -OH, C 1 to C 2 alkoxy and C 1 to C 2 alkyl; - Z represents a moiety capable of coordinating to the radionuclide. - R represents arginine or N-methyl arginine; - G represents glycine; - D represents aspartic acid; - Y 1 is an amino acid residue selected from aspartic acid, glutamic acid, asparagine, glutamine, lysine and arginine wherein the side-chain of Y 1 is bonded via a heteroatom in the side-chain to the moiety -L-Z; - The moieties -Y 2 -S- and -Y 3 -S- each independently represent an amino acid residue capable of forming a disulphide bond -Y 2 -S-S-Y 3 -; - Y 4 is an amino acid residue selected from valine, leucine, isoleucine, methionine, phenylalanine, tyrosine and tryptophan; - The moiety -Y 5 -(CH 2) p -S- represents a sulphur-containing amino acid residue; wherein p is 1 or 2; - R 1 represents -(CH 2) q -(Ar) r -(CH 2) s -, wherein q and s are each independently 0 or an integer, wherein q + s is an integer from 1 to 8, and wherein r is 0 or 1; and wherein Ar is a C 6 arylene group; - R 2 is absent or represents -Het-((CH 2) n Het) m R b HetR a; - n is 1 or 2; - m is an integer from 1 to 6; - each Het is independently -O- or -NR a -; - R b is absent or is C 1 to C 6 alkylene which may be optionally substituted by from 1 to 3 oxo groups and/or may be interrupted by from 1 to 3 groups selected from -O- and -C -; - each R a is independently selected from H and C 1 to C 2 alkyl; - L is -C -(C 1 -C 6 alkylene)-C -; wherein the alkylene group of L may be optionally interrupted by -O- and/or wherein the alkylene group of L is unsubstituted or substituted by 1 or 2 substituents selected from -OH, C 1 to C 2 alkoxy and C 1 to C 2 alkyl; - Z represents a moiety capable of coordinating to the radionuclide.