It has been reported that administration of the paramagnetic contrast agent Gd-diethylenetriaminepentaacetic acid (Gd-DTPA, gadopentate) prior to Ga-67 citrate could lead to poor quality scans, characterized by pronounced bone uptake and a loss of tumour avidity. Suggestions to account for this behaviour included in vivo dissociation or the presence of free DTPA in the formulation. The objective of this study was to assess this potential interference in Ga-67 imaging using a mouse model. Commercial gadopentate and gadodiamide contrast agents at doses up to 5 mmol.kg(-1) were injected into mature female Balb/c mice 4 h before i.v. Ga-67 citrate, then the biodistribution was determined at 24 h. Gd-DTPA solutions containing excess Gd or DTPA were examined as well. The model was verified by identical studies using inactive Ga(III) or Fe(III) at 0.1 mmol.kg(-1). The effects of Gd(III) or the DTPA ligand at this dose were also determined. Administration of Gd-DTPA was found to produce no marked changes in Ga-67 biodistribution. Minor changes occurred after 0.1 mmol.kg(-1) Gd(III) or the DTPA ligand, but could not account for the scan changes reported above. Inactive Ga(III) or Fe(III), as expected, caused a marked reduction of Ga-67 uptake in all tissues except bone, leading to greatly increased total bone:total soft tissue ratios. It is concluded that Gd-DTPA or its constituents do not significantly alter the biodistribution of Ga-67 citrate in mice. Extrapolating these findings to the human situation suggests that the previously reported scan changes may have been the result of other undetermined factors. ((C) 2002 Lippincott Williams Wilkins).
