Magnetic Resonance Spectroscopy of Rat Skeletal Muscles. An Application to the Estimation of the Postmortem Interval.

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It is considered that the fall in ATP content is directly related to the onset of rigor mortis. Therefore, ATP content in the skeletal muscle is a factor which has been considerd to be of value in estimating the postmortem intaerval. Using conventional techniques, however, it is difficlt to quantify high phosphate compounds accurately in the biological materials. The ^<31>P-MRS can be used to measure ATP,phosphocreatine (PCr) and inorganic phosphate (Pi) very rapidly and noninvasively in biological tissues. Intracellular pH value can also be determined using the chemical shift of Pi. The operation and the interpretation of the spectrum is relatively simple, so it is easy to master the technique. For the purpose of evaluate the possibility of the application of ^<31>P-MRS to the estimation of the postomortem interval, we analyzed high energy phosphate compounds in the skeletal muscles of the dead rats using the ^<31>P-MRS and examined the association between the analytical results and p … More ostmortem intervals. The animals were killed in cases of strangulation, nitrogen asphyxia, drowning, or fatal intoxications due to CO gas, methamphetamine, cocaine, ethanol or KC1. ^<31>P-MRS was performed using the surface coil technique up to 4 hours after death. Signal intensities of the peaks in the spectra and the pH values in the tissues were calculated. Correlation analysis was used to estimate the strength of the association between the postmortem interval and the content of ATP,PCr and Pi, and the pH value in the tissues. Regression analysis was also used to estimate the postmortem interval from ^<31>P-MRS data. In any mode of killing, PCr and ATP decreased after death, whereas Pi increased with time. The pH value was decreased linearly in the early stage after death. In the tissues of the rats killed in the relativeabsence of muscular activity before death, the reduction of the PCr and ATP content was relatively slow. When the rats died following hard exercise, struggle or convulsions, the fall in PCr and ATP content was accelerated. Among all the mode of killing, there was little variation in the decreasing rate of the pH value. In any mode of killing, all ^<31>P-MRS data indicated significant correration with postmortem interval. There was a close relation between the pH in the tissue and postmortem interval. Least squares regression analysis to estimate the postmortem interval from the ^<31>P-MRS data was successful. R squared values calculated were high, althogh the data points showed some degree of scatter. Our present results suggest that ^<31>P-MRS data can be used as a means to estimate the time of death. Especially, in the early stage after death, the pH value is generally ragarded as providing one of the most reliable ways of estimating the time of death. Less