Detection of Inflammatory Arthritis by Using Hyperpolarized 13C-Pyruvate with MR Imaging and Spectroscopy

Purpose: To examine the feasibility of using magnetic resonance (MR) spectroscopy with hyperpolarized carbon 13 (C-13)-labeled pyruvate to detect inflammation. Materials and Methods: The animal care and use committee approved all work with animals. Arthritis was induced in the right hind paw of six rats; the left hind paw served as an internal control. The lactate dehydrogenase-catalyzed conversion of pyruvate to lactate was measured in inflamed and control paws by using C-13 MR spectroscopy. Clinical and histologic data were obtained to confirm the presence and severity of arthritis. Hyperpolarized C-13-pyruvate was intravenously injected into the rats before simultaneous imaging of both paws with C-13 MR spectroscopy. The Wilcoxon signed rank test was used to test for differences in metabolites between the control and arthritic paws. Results: All animals showed findings of inflammation in the affected paws and no signs of arthritis in the control paws at both visible inspection (clinical index of 3 for arthritic paws and 0 for control paws) and histologic examination (histologic score of 3-5 for arthritic paws and 0 for control paws). Analysis of the spectroscopic profiles of C-13-pyruvate and converted C-13-lactate showed an increase in the amount of C-13-lactate in inflamed paws (median lactate-to-pyruvate ratio, 0.50; mean lactate-to-pyruvate ratio +/- standard deviation, 0.52 +/- 0.16) versus control paws (median lactate-to-pyruvate ratio, 0.27; mean lactate-to-pyruvate ratio, 0.32 +/- 0.11) (P < .03). The ratio of C-13-lactate to total C-13 was also significantly increased in inflamed paws compared with control paws (P < .03). Conclusion: These results suggest that alterations in the conversion of pyruvate to lactate as detected with C-13-MR spectroscopy may be indicative of the presence of inflammatory arthritis. (C) RSNA, 2011