In Situ pH Determination Using ¹H-MRS Acetate Chemical Shift for Noninvasive Postmortem Examinations

Magnetic resonance spectroscopy provides novel noninvasive tools for postmortem forensic investigations. While postmortem temperature assessment using ¹H-MRS has recently been established, noninvasive determination of brain tissue pH remains largely unexplored despite evidence linking pH to the cause of death. In this study, we investigated the feasibility of in situ brain pH determination using postmortem ¹H-MRS based on the chemical shift difference between myo-inositol (mI, reference metabolite) and acetate (Ace, indicator metabolite) in 58 decedents. LCModel-based fitting strategies were evaluated using simulations that mimic postmortem brain ¹H-MRS spectra in order to identify the most accurate and precise approach and to assess factors affecting chemical shift determination. The in situ MRS data were subsequently analyzed using the optimal strategy. Brain pH values derived from the mI-Ace chemical shift difference were validated against pH measurements obtained from homogenized brain tissue samples. Our results demonstrate that the optimal fitting is achieved by allowing increased flexibility in the chemical shift determination of Ace. Using this approach, robust detection of low pH values in postmortem brain tissue is achieved. These findings demonstrate the feasibility of Ace-based ¹H-MRS for noninvasive in situ assessment of postmortem brain pH and indicate its potential for forensic applications.