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Technetium-99m-Labeled Stannous Imidodiphosphate, A New Radiodiagnostic Agent for Bone Scanning: Comparison with Other ^99mTc Complexes

Upstate Medical Center, Syracuse, New York

Correspondence: For reprints contact: G. Subramanian, Div. of Nuclear Medicine, Dept. of Radiology, Upstate Medical Center, Syracuse, N.Y. 13210.

ABSTRACT

Imidodiphosphate (IDP) is an analog of pyrophosphate and diphosphonate, with a P-N-P bond instead of P-O-P or P-C-P. We have labeled IDP with ^99mTc quantitatively (98%) using stannous ions as the reducing/complexing agent in a freeze-dried kit form. Radiobioassay of this compound was carried out in rabbits and the results were compared with those of eight other Tc-labeled bone-imaging agents, using the performance of simultaneously administered ⁸⁵Sr as a reference standard. The ^99mTc-IDP concentrated 20% higher in the bone, and its soft-tissue and blood levels were lower than with ⁸⁵Sr. By comparison, the concentrations in the bone of the other ^99mTc agents were 20% less than that of ⁸⁵Sr. Regarding blood levels, Tc-IDP performed worse than the Tc-diphosphonate but better than the pyrophosphate and the other technetium complexes. Scintillation camera images of ^99mTc-IDP in both rabbits and dogs showed excellent details of the skeleton. In a preliminary human study, images with ^99mTc-IDP were somewhat inferior to those comparably procured with ^99mTc-methylene diphosphonate, but count rates with the IDP complex were about twice those with the MDP compound. Because of its better bone uptake, however, it is suggested that ^99mTc-IDP may be clinically useful in spite of its relatively slow blood clearance.

Key Words: IDP, imidodiphosphate • MDP, methylene diphosphonate • HEDP, ethylenehydroxydiphosphonate • AEDP, aminoethylenediphosphonate • HMDTMP, hexamethylenediaminotetra(methylene phosphonate) • EDTMP, ethylenediaminotetra(methylene phosphonate) • DTPMP, diethylenetriaminopenta(methylene phosphonate)