Fig. 5.

Metabolite data from mTBI patients (blue stars) and controls (red asterisks) for (a.) global WM NAA, (b.) mI and (c.) NAA/mI, with fitted normal distributions (solid red: controls; dashed blue: patients): ${\mu }_{\text{NAA}}^{(\text{controls})}=7.74\pm 0.62\text{mM}$, ${\mu }_{\text{NAA}}^{(\text{patients})}=7.19\pm 0.83\text{mM}$, ${\mu }_{\text{mI}}^{(\text{controls})}=4.4\pm 0.56\text{mM}$, ${\mu }_{\text{mI}}^{(\text{patients})}=4.574\pm 0.65\text{mM}$, ${\mu }_{\text{ratio}}^{(\text{controls})}=1.76\pm 0.27$, ${\mu }_{\text{ratio}}^{(\text{patients})}=1.57\pm 0.29$. NAA decreases and mI slightly increases, with the only statistically significant change being that of NAA as determined by a double-sided t-test (p=0.042). Note the increased variability of the ratio distribution in (c), introduced by dividing by mI. The sample sizes required to observe each change (Eq. [4]) are N_NAA=10, N_mI=72, N_NAA/mI=14, and the AUROCs are AUROC_NAA=0.70, AUROC_mI=0.58, AUROC_NAA/mI=0.68, showing absolute quantification is superior to metabolic ratios in detecting mTBI WM injury.