Fig. 3

31P-Magnetic resonance spectroscopy imaging for the assessment of in vivo mitochondrial bioenergetics. 31P-MRSI spectra of a representative subset of brain parenchyma will be taken using a double-tuned P-headcoil (Advanced Imaging Research, Cleveland, Ohio). To attain sufficient relaxation of the phosphorus metabolites, a repetition time of 4500 ms will be used together with a three-dimensional chemical shift imaging sequence (6 × 5 × 3 voxel, 6 kHz bandwidth, 1024 data points, 8:51 min measuring time). The analysis procedures will follow an updated version of an already published protocol with an optimization of data acquisition. Peak positions and intensities will be calculated with the AMARES algorithm. We will examine adenosine triphosphate (ATP) and phosphocreatine (PCr), which reflects the overall high-energy phosphate turnover. PCr represents a high-energy reservoir linked to ATP in a bidirectional reaction in which ATP is formed by PCr and vice versa. In addition to PCr and ATP, the ratios of PCr/inorganic phosphate (iP) and ATP/Pi will be evaluated as an indicator of intracellular energy status within the scope of this study. A: 31P-MRSI spectrum. B: model fit on 31P-MRSI spectrum. C: background noise