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  Amide proton signals as pH indicator for in vivo MRS and MRI of the brain: Responses to hypercapnia and hypothermia.

Watanabe, T., Frahm, J., & Michaelis, T. (2016). Amide proton signals as pH indicator for in vivo MRS and MRI of the brain: Responses to hypercapnia and hypothermia. NeuroImage, 133, 390-398. doi:10.1016/j.neuroimage.2016.03.013.

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 Creators:
Watanabe, T.1, Author           
Frahm, J.1, Author           
Michaelis, T.1, Author           
Affiliations:
1Biomedical NMR Research GmbH, MPI for biophysical chemistry, Max Planck Society, ou_578634              

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Free keywords: Creatine phosphokinase; Glutamine; Hypercapnia; Hypothermia; Proton exchange; Saturation transfer
 Abstract: Using proton MRS and MRI of mouse brain at 9.4T, this work provides the first in vivo evidence of pH-dependent concurrent changes of three amide signals and related metabolic responses to hypercapnia and hypothermia. During hypercapnia, amide proton MRS signals of glutamine at 6.8-6.9ppm and 7.6ppm as well as of unspecific compounds at 8.1-8.3ppm increase by at least 50% both at 37°C and 22°C. These changes reflect a reduced proton exchange with water. They are strongly correlated with intracellular pH which ranges from 6.75±0.10 to 7.13±0.06 as determined from a shift in creatine phosphokinase equilibrium. In MRI, saturation transfer from aliphatic as well as aromatic and/or amide protons alters slightly during hypercapnia and significantly during hypothermia. The asymmetry in magnetization transfer ratios decreased slightly during hypercapnia and hypothermia. Regardless of pH or temperature, saturation transfer from aliphatic protons between -2 and -4ppm frequency offset to water protons is significantly greater than that from aromatic/amide protons at corresponding offsets between +2 and +4ppm. Irradiation of aliphatic compounds at -3.5ppm frequency offset from water predominantly saturates lipids and water associated with myelin. Taken together, the results indicate that, for the B1 power used in this study, dipolar coupling between aliphatic and water protons rather than proton exchange is the dominant factor in Z-spectra and magnetization transfer ratio asymmetry of the brain in vivo.

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Language(s): eng - English
 Dates: 2016-03-112016-06
 Publication Status: Issued
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 Rev. Type: Peer
 Identifiers: DOI: 10.1016/j.neuroimage.2016.03.013
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Title: NeuroImage
Source Genre: Journal
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Pages: - Volume / Issue: 133 Sequence Number: - Start / End Page: 390 - 398 Identifier: -