Fig 1.
Plasma color inspection and the A414 values.
A typical change in plasma color was compared with the average absorbance measured at 414 nm and the standard deviations. *P < 0.05 indicates a significant difference from the 0-h group.
Table 1.
Major band assignments of the FTIR spectrum of plasma and formed elements on the 1800–900 cm−1 spectral range [44, 46–48, 67–70].
Fig 2.
The raw ATR–FTIR spectra and average second-derivative spectra.
(A) Raw ATR–FTIR spectra obtained from postmortem plasma. (B) Average SNV-corrected, second-derivative ATR–FTIR spectra of the calibration set plasma obtained from different PMIs. Arrows indicate the major change trends in the intensity of the marked bands with PMI. Inset: local magnification image corresponding to the frame area marked in.
Table 2.
Results of cross-validation and predictive ability of the full-spectrum model and GA-PLS model.
Fig 3.
Predicted versus actual PMI from the calibration and prediction sets.
(A) Prediction results using the full-spectrum PLS model and (B) using the GA-PLS model. The green lines are the reference line corresponding to the perfect prediction.
Fig 4.
The results of VIP scores and GA-PLS.
(A) VIP score distribution for the investigated spectral region 1800–900 cm–1. The gray line shows the average preprocessed spectrum, and the orange line shows the threshold value. (B) Frequency of the selection of different wavenumbers in the 100 runs of GA-PLS. The average preprocessed spectrum is superimposed on the frequency.
Fig 5.
Comparison of spectra of 0-h plasma and formed elements.
Arrows denote the spectral differences at corresponding bands in Fig 2B and point the direction from 0-h plasma to formed elements. Informative spectral subsets selected most frequently by GA-PLS (greater than 50%) are represented in gray, and others are in white.
Fig 6.
Average similarity index and the standard deviations at each PMI point.
The spectra from different PMI plasma groups were compared with the averaged spectrum from 0-h formed elements using (A) full-spectrum subsets, (B) selected subsets, and (C) eliminated subsets by the GA-PLS model. *P < 0.05 indicates a significant difference from the 0-h group.
Fig 7.
Order and degree of postmortem changes in blood after death as time progresses.
The blue lines represent cell membranes (solid lines: intact; dotted line: broken-down), and the black arrows represent the effects of redistribution.