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Journal Article

Volumetric mapping of intra- and extracellular pH in the human brain using 31P MRSI at 7T

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Korzowski, A., Weinfurtner, N., Mueller, S., Breitling, J., Goerke, S., Schlemmer, H.-P., et al. (2020). Volumetric mapping of intra- and extracellular pH in the human brain using 31P MRSI at 7T. Magnetic Resonance in Medicine, 84(4), 1707-1723. doi:10.1002/mrm.28255.

Cite as: https://hdl.handle.net/21.11116/0000-000C-AA38-6

Purpose: In vivo 31 P MRSI enables noninvasive mapping of absolute pH values via the pH-dependent chemical shifts of inorganic phosphates (Pi ). A particular challenge is the quantification of extracellular Pi with low SNR in vivo. The purpose of this study was to demonstrate feasibility of assessing both intra- and extracellular pH across the whole human brain via volumetric 31 P MRSI at 7T.
Methods: 3D 31 P MRSI data sets of the brain were acquired from three healthy volunteers and three glioma patients. Low-rank denoising was applied to enhance the SNR of 31 P MRSI data sets that enables detection of extracellular Pi at high spatial resolutions. A robust two-compartment quantification model for intra- and extracellular Pi signals was implemented.
Results: In particular low-rank denoising enabled volumetric mapping of intra- and extracellular pH in the human brain with voxel sizes of 5.7 mL. The average intra- and extracellular pH measured in white matter of healthy volunteers were 7.00 ± 0.00 and 7.33 ± 0.03, respectively. In tumor tissue of glioma patients, both the average intra- and extracellular pH increased to 7.12 ± 0.01 and 7.44 ± 0.01, respectively, compared to normal appearing tissue.
Conclusion: Mapping of pH values via 31 P MRSI at 7T using the proposed two-compartment quantification model improves reliability of pH values obtained in vivo, and has the potential to provide novel insights into the pH heterogeneity of various tissues.