## 3 Results
### Regional-Level Comparison and ROI-Specific Differences  
Comparison of these regions revealed statistically significant differences between image techniques (Figure 6). (See Appendix A Table A1 for comparisons across all regions). The right anterior cingulate cortex (Cingulate_Ant_R) was the only region that displayed significant variation across all image techniques (\(p\) = 0.043, SPECT vs. tcMRI; \(p\) = 0.029, SPECT vs. MRI; \(p\) = 0.009, tcMRI vs. MRI). The right frontal lobe (Frontal_Mid_2_R) exhibited significant CVR differences between SPECT and MRI (\(p\) = 0.045) and between tcMRI and MRI (\(p\) = 0.003). Although a significant difference was observed in the left olfactory cortex (Olfactory_L) across image techniques (\(p\) = 0.028), post hoc analysis did not reveal significant pairwise comparisons. The greatest number of regions with significant differences in CVR were observed between tcMRI and MRI. Significant differences be-tween tcMRI and MRI were observed in eight regions: left anterior orbital gyrus (OFCant_L) (\(p\) = 0.006), \begin{table}
\begin{tabular}{c c c c|c c c c|c c c} \hline \multirow{2}{*}{**Participants**} & \multirow{2}{*}{**Age**} & \multirow{2}{*}{**Gender**} & \multirow{2}{*}{**Hand**} & \multicolumn{5}{c|}{**SPECT**} & \multicolumn{2}{c}{**fMRI**} \\ \cline{4-11}  & & & & **Pre BP** & **Post BP** & **Gas** & **Count1 st** & **Count2 nd** & **Pre BP** & **Post BP** \\ \hline
01 & 25 & M & Rt & 116/59 & 125/95 & CO\({}_{2}\) & 3593 & 10,599 & 117/77 & 112/80 \\
02 & 22 & F & Rt & 99/56 & 114/66 & CO\({}_{2}\) & 5223 & 15,440 & 107/60 & 102/58 \\
03 & 25 & M & Rt & 134/82 & 136/90 & CO\({}_{2}\) & 3543 & 10,453 & 134/97 & 134/84 \\
04 & 21 & F & Rt & 91/52 & 98/60 & CO\({}_{2}\) & 3486 & 12,876 & 105/67 & 100/67 \\
05 & 27 & M & Rt & 123/73 & 122/75 & CO\({}_{2}\) & 4222 & 12,963 & 111/68 & 110/74 \\
06 & 25 & M & Rt & 123/67 & 130/76 & CO\({}_{2}\) & 4335 & 13,327 & 125/81 & 126/74 \\
07 & 23 & M & Rt & 119/60 & 122/67 & CO\({}_{2}\) & 3555 & 12,272 & 108/65 & 111/66 \\
08 & 23 & M & Rt & 118/71 & 123/80 & AIR & 4072 & 12,220 & 125/86 & 135/91 \\
09 & 23 & M & Rt & 124/55 & 137/70 & AIR & 4208 & 12,649 & 121/75 & 137/76 \\ \hline \end{tabular}
\end{table} 
Table 1: Demographic information. left anterior cingulate cortex (Cingulate_Ant_L) (\(p\) = 0.004), left pallidum (Pallidum_L) (\(p\) = 0.004), left midcingulate cortex (Cingulate_Mid_L) (\(p\) < 0.001), right frontal lobe (Frontal_Mid_2_R) (\(p\) = 0.003), right midcingulate cortex (Cingu-late_Mid_R) (\(p\) < 0.001), right caudate (Caudate_R) (\(p\) = 0.003), and left Rolandic operculum (Rolandic_Oper_L) (\(p\) < 0.001). Figure 5: Mean cerebrovascular reactivity (CVR) maps and values. (**A**) Representative mean CVR maps. (**a**) Single photon emission computed tomography (SPECT) carbon dioxide (CO\({}_{2}\)) CVR maps. (**b**) The stimulus timing corrected functional magnetic resonance imaging (tcMRI) CO\({}_{2}\) CVR maps. (**c**) Magnetic resonance imaging CO\({}_{2}\) CVR maps. The color bar represents CVR values. (**B**) Mean CVR values of all seven participants. Error bars show standard deviation (SD). Asterisks (*) denote statistically significant differences. Figure 6: Comparison of cerebrovascular reactivity (CVR) in the top 30% regions for tcMRI, MRI, and SPECT. This graph displays the CVR values for the top 30% of regions showing the highest CVR as determined by SPECT CVR in the healthy participants cohort. Corresponding CVR values from tcMRI and conventional MRI are shown for these selected regions. Error bars represent standard deviation. Regions with statistically significant changes in the post hoc analysis between the modalities within these top 30% regions are marked with asterisks (*): red asterisks for significant differences between SPECT and MRI, green asterisks for differences between SPECT and tcMRI, and black asterisks for differences between tcMRI and MRI.