An imaging agent which comprises an 18 F-radiolabelled c-Met binding cyclic peptide, wherein said c-Met binding cyclic peptide is an 18 to 30-mer cyclic peptide of Formula I: Z 1 -[cMBP]-Z 2 where: cMBP is of Formula II: - x-Q-(A') y - where Q is the amino acid sequence (SEQ-1): -Cys a -X 1 -Cys c -X 2 -Gly-Pro-Pro-X 3 -Phe-Glu-Cys d -Trp-Cys b -Tyr-X 4 -X 5 -X 6 - wherein X 1 is Asn, His or Tyr; X 2 is Gly, Ser, Thr or Asn; X 3 is Thr or Arg; X 4 is Ala, Asp, Glu, Gly or Ser; X 5 is Ser or Thr; X 6 is Asp or Glu; and Cys a-d are each cysteine residues such that residues a and b as well as c and d are cyclised to form two separate disulfide bonds; A and A' are independently any amino acid other than Cys, with the proviso that at least one of A and A' is present and is Lys; x and y are independently integers of value 0 to 13, and are chosen such that [x + y] = 1 to 13; Z 1 is attached to the N-terminus of cMBP, and is H or M IG; Z 2 is attached to the C-terminus of cMBP and is OH, OBc, or M IG, where B c is a biocompatible cation; each M IG is independently a metabolism inhibiting group which is a biocompatible group which inhibits or suppresses in vivo metabolism of the cMBP peptide at either the amino terminus (Z 1) or carboxy terminus (Z 2) and which chosen from: for the peptide amine terminus: N-acylated groups -NH(C=O)R G where the acyl group -(C=O)R G has R G chosen from: C 1-6 alkyl, or C 3-10 aryl groups or comprises a polyethyleneglycol building block; for the peptide carboxy terminus: carboxamide, tert-butyl ester, benzyl ester, cyclohexyl ester, amino alcohol or a polyethyleneglycol building block; wherein cMBP is labelled at the Lys residue of the A or A' groups with 18 F. cMBP is of Formula II: - x-Q-(A') y - where Q is the amino acid sequence (SEQ-1): -Cys a -X 1 -Cys c -X 2 -Gly-Pro-Pro-X 3 -Phe-Glu-Cys d -Trp-Cys b -Tyr-X 4 -X 5 -X 6 - wherein X 1 is Asn, His or Tyr; X 2 is Gly, Ser, Thr or Asn; X 3 is Thr or Arg; X 4 is Ala, Asp, Glu, Gly or Ser; X 5 is Ser or Thr; X 6 is Asp or Glu; and Cys a-d are each cysteine residues such that residues a and b as well as c and d are cyclised to form two separate disulfide bonds; A and A' are independently any amino acid other than Cys, with the proviso that at least one of A and A' is present and is Lys; x and y are independently integers of value 0 to 13, and are chosen such that [x + y] = 1 to 13; where Q is the amino acid sequence (SEQ-1): -Cys a -X 1 -Cys c -X 2 -Gly-Pro-Pro-X 3 -Phe-Glu-Cys d -Trp-Cys b -Tyr-X 4 -X 5 -X 6 - wherein X 1 is Asn, His or Tyr; X 2 is Gly, Ser, Thr or Asn; X 3 is Thr or Arg; X 4 is Ala, Asp, Glu, Gly or Ser; X 5 is Ser or Thr; X 6 is Asp or Glu; and Cys a-d are each cysteine residues such that residues a and b as well as c and d are cyclised to form two separate disulfide bonds; X 1 is Asn, His or Tyr; X 2 is Gly, Ser, Thr or Asn; X 3 is Thr or Arg; X 4 is Ala, Asp, Glu, Gly or Ser; X 5 is Ser or Thr; X 6 is Asp or Glu; and Cys a-d are each cysteine residues such that residues a and b as well as c and d are cyclised to form two separate disulfide bonds; A and A' are independently any amino acid other than Cys, with the proviso that at least one of A and A' is present and is Lys; x and y are independently integers of value 0 to 13, and are chosen such that [x + y] = 1 to 13; Z 1 is attached to the N-terminus of cMBP, and is H or M IG; Z 2 is attached to the C-terminus of cMBP and is OH, OBc, or M IG, where B c is a biocompatible cation; each M IG is independently a metabolism inhibiting group which is a biocompatible group which inhibits or suppresses in vivo metabolism of the cMBP peptide at either the amino terminus (Z 1) or carboxy terminus (Z 2) and which chosen from: for the peptide amine terminus: N-acylated groups -NH(C=O)R G where the acyl group -(C=O)R G has R G chosen from: C 1-6 alkyl, or C 3-10 aryl groups or comprises a polyethyleneglycol building block; for the peptide carboxy terminus: carboxamide, tert-butyl ester, benzyl ester, cyclohexyl ester, amino alcohol or a polyethyleneglycol building block; where B c is a biocompatible cation; each M IG is independently a metabolism inhibiting group which is a biocompatible group which inhibits or suppresses in vivo metabolism of the cMBP peptide at either the amino terminus (Z 1) or carboxy terminus (Z 2) and which chosen from: for the peptide amine terminus: N-acylated groups -NH(C=O)R G where the acyl group -(C=O)R G has R G chosen from: C 1-6 alkyl, or C 3-10 aryl groups or comprises a polyethyleneglycol building block; for the peptide carboxy terminus: carboxamide, tert-butyl ester, benzyl ester, cyclohexyl ester, amino alcohol or a polyethyleneglycol building block; for the peptide amine terminus: N-acylated groups -NH(C=O)R G where the acyl group -(C=O)R G has R G chosen from: C 1-6 alkyl, or C 3-10 aryl groups or comprises a polyethyleneglycol building block; for the peptide carboxy terminus: carboxamide, tert-butyl ester, benzyl ester, cyclohexyl ester, amino alcohol or a polyethyleneglycol building block;