The effect of gadolinium-based MRI contrast agents on the biodistribution of (67)Ga.

Abstract

It has been reported that administration of the paramagnetic contrast agent Gd-diethylenetriaminepentaacetic acid (Gd-DTPA, gadopentate) prior to 67Ga 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 67Ga imaging using a mouse model. Commercial gadopentate and gadodiamide contrast agents at doses up to 5mmol*kg(-1) were injected into mature female Balb/c mice 4h before i.v. 67Ga citrate, then the biodistribution was determined at 24h. 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 0.1mmol*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 67Ga biodistribution. Minor changes occurred after 0.1mmol*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 67Ga 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 67Ga 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.