Fig. 6. In vivo APTw vs. pH_enh results of hypercapnia and hyperoxia challenge.

10% CO₂ gas was used to induce tissue acidosis and 70% O₂ gas was used as a control experiment. Percent change maps of (A) APTw and (B) pH_enh induced by 10% CO₂ challenge, and (C) pH_enh during 70% O₂ challenge were overlaid on EPI images. (D) Time courses were obtained from the cortical ROI (delineated in C by green countours). Error bars: SD (n = 4), the black horizontal bar, time of gas challenge. During the acidosis-inducing CO₂ challenge, APTw signal decreases slightly, whereas pH_enh shows a much larger signal increase. In a control experiment, pH_enh shows a minimal response during O₂ challenge, which induces blood flow and volume changes without acidosis.