Variations in quality of bone images obtained with four different preparations of MDP

Technetium 99m medronate (MDP) is widely used for bone imaging. While all MDP kits are based on the reduction of pertechnetate in the presence of methylenediphosphonic acid, there are numerous differences in the formulations of kits from different suppliers. Among these differences are the form of methylenediphosphonic acid used (free acid or sodium salt), the reducing agent (stannous chloride or fluoride), the use of an antioxidant (ascorbic acid), and the ratio of the reactants. Direct comparison of the images obtained using four commercial MDP formulations in an animal model revealed significant variation in image quality. The study was set up so that observers compared images obtained with the four MDPs in each of three rabbits. They ranked the images according to quality and were not aware that they were comparing the four MDPs in each of the rabbits. Bone/soft tissue ratios calculated from digital images showed the pattern expected from observers' preferences: higher for the MDP formulation which received the best rankings. Similarities were noted in the formulations of the kits which gave images judged to be superior. The inclusion of MDP as the disodium salt, a lower ratio of reducing agent to the complexing agent, and the absence ofmore » antioxidant were common factors in the formulations which gave images judged to be better. It is possible that the observed variation in image quality is due to the formation of more than one labeled species in MDP kits.« less