In vivo H1 MR spectroscopy using 3 Tesla to investigate the metabolic profiles of joint fluids in different types of knee diseases

In vivo proton (1H) magnetic resonance spectroscopy (MRS) has not yet been systematically used to study joint fluids in human knees. The objective of this study, therefore, was to assess the ability of proton MRS to identify the apparent heterogeneous characteristics of metabolic spectra in the joint fluid regions in human knees using a high-field MRI system. Eighty-four patients with effusion lesions who were referred for routine knee MR imaging underwent proton MRS with point-resolved, single-voxel MR spectroscopy using a clinical 3.0 Tesla MRI system. Thirty-eight patients were confirmed to have the following: degenerative osteoarthritis, 21 patients (Group 1); traumatic diseases, 12 patients (Group 2); infectious diseases, 4 patients and an inflammatory disease, 1 patient (Group 3). Spectroscopy data were analyzed using the public jMRUI freeware software to obtain lipid metabolites. Nonparametric statistical comparisons were performed to investigate any differences in metabolites among the three disease groups. The major metabolites were vinylic CH=CH lipids around 5.1-5.5 ppm, CH2 lipids around 1.1-1.5 ppm, and CH3 lipids around 0.7-1.0 ppm. Each patient had either a CH=CH lipid peak, CH2 and CH3 lipid peaks, or all three peaks. There were no significant differences among the three groups for the CH3 (p = 0.9019), CH2 (p= 0.6406), and CH=CH lipids (p = 0.5467) and water (p = 0.2853); none of the metabolites could differentiate between any of the three types of diseases. The CH2 lipids in the 38 patients who had confirmed fluid characteristics were significantly correlated with CH3 lipids (rho = 0.835, p < 0.0001). The ratio of CH3 to CH2 was highest in the degenerative disease. In both the degenerative and traumatic diseases, metabolite peaks of the vinylic CH=CH lipids around 5.1-5.5 ppm and of the sum of the CH2 and CH3 lipids around 0.7-1.5 ppm were observed, but in the infectious disease, only a metabolite peak of the sum of the CH2 and CH3 lipids was detected. Although none of the metabolites could statistically significantly differentiate between the three types of diseases, the different lipid metabolite peaks and their ratios in the three disease groups may give us a hint at the different mechanisms of joint fluids in the infectious, degenerative, and traumatic diseases.