Magnetic Resonance Spectroscopy

MRS technology is based on the fact that MR acquisition involves receiving echoed RF waves of multiple cellular chemical constituents. The individual chemical and metabolite constituents could be measured by suppressing the resonance frequency of water molecules. A detailed exposition of the various types of MRS techniques is beyond the scope of this chapter, and the reader is referred to excellent reviews on the topic (Mason and Krystal 2006; C. M. Moore et al. 1999). Among the markers currently being researched are M-acetylaspartate (NAA), glutamate/glutamine (glx), myoinositol (ml), choline (Cho), glutathione, creatine, GABA, phosphomonoester (PME), and phosphodiester (PDE) (Lyoo and Renshaw 2002). An example of an MRS spectrum from a healthy control subject is provided in Figure 10-6. Using this approach, Frye et al. (2007)were able not only to demonstrate elevated glutamate/glutamine (glx) in anterior cingulate/medial prefrontal areas of patients with bipolar depression but also to document the reduction of glutamine among patients who showed clinical response to treatment with lamotrigine. Using proton MRS, C. M. Moore et al. (2007) measured multiple metabolites in the anterior cingulate cortex (ACC) of children with bipolar disorder and reported decreased glutamine concentrations in the presence of normal glutamate levels. Using another sample of adult patients, these same authors reported that anterior cingulate cortex glutamine levels were elevated rapidly following administration of the anticonvulsant topiramate (C. M. Moore et al. 2006). Using MRS technology, Sanacora et al. (2003) reported that cortical GABA concentrations increased following a course of electroconvulsive therapy and used this information to hypothesize that this increase in GABA might be associated with clinical recovery. Thus, MRS might provide very useful biomarkers of neural functioning and disease states among patients with psychiatric disorders.

FIGURE 10-6. Proton magnetic resonance spectroscopy (MRS) spectrum from right dorsolateral prefrontal cortex voxel of a healthy individual.

MM = macromolecules; NAA = N-acetylaspartate; Glx = glutamate/glutamine; Cr/PCr = creatine/phosphocreatine; Ch = choline; ml = myoinositol.

Source. Reprinted from Haroon E, Watari K, Thomas MA, et al.: "Prefrontal Myo-Inositol Concentration and Visuospatial Functioning Among Diabetic Depressed Patients." Psychiatry Research: Neuroimaging 171:10-19, 2009. Copyright 2009, Elsevier Ltd. Used with permission.

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