Characterization of molecular imaging probes in multiple animal models of disease is essential to increase their diagnostic potential. For example, we recently demonstrated visualization of active inflammation in a rabbit model saccular aneurysm using clinical field strength MRI and the paramagnetic MR contrast agent di-5-HT-GdDTPA, which has been shown in vitro to be sensitive and specific for the enzyme myeloperoxidase (MPO). While the use of transgenic mice (MPO−/−) has demonstrated specificity of di-5-HT-GdDTPA for MPO in a model of myocardial infarction [1], MPO-deficient rabbits are not available. Therefore, in this study, we sought to validate di-5-HT-GdDTPA MPO specificity in the New Zealand white rabbit by comparing serial enhancement ratios of di-5-HT-GdDTPA to a structurally similar MR contrast agent, di-Tyr-GdDTPA, which is activated by peroxidases but not by MPO. Structural diagrams of the synthesis of the two agents are demonstrated in Figure 1 [2].

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