Regression analysis of metabolite concentrations estimated from localized proton MR spectra of active and chronic multiple sclerosis lesions.

Localized short echo time magnetic resonance (MR) spectra were obtained from patients with multiple sclerosis of relapsing-remitting or secondary chronic-progressive course and from healthy controls. Automated analysis using model spectra, sensitivity correction, and subtraction of partial ventricular volume yielded tissue concentrations of metabolites that were in line with findings of previous studies. Additional findings were increased creatine in chronic lesions and increased myo-inositol in normal-appearing white matter. Regression analysis was performed to reveal concomitant changes of metabolite concentrations. Differences in the correlations between cholines and myo-inositol suggest increased expression of myo-inositol in chronic lesions or of cholines in active, contrast-enhanced lesions. A correlation between N-acetyl-aspartate and creatine, which is probably due to extracellular edema, was observed in active but not in chronic lesions. Creatine and cholines correlated in chronic lesions, which may be the result of gliosis. The consequences of these findings for the interpretation of absolute concentrations and creatine ratios are discussed.