## 3 Results  
### Participants  
General patient data can be found in Table 1. In total, the structural and functional MRI data sets, DSA data sets and neurological assessments of 69 patients were included in the study. Eight patients had prior revascularization surgery; consequently, 130 ICAterritories and 260 ACA/MCA territories were evaluated with regard to the first aim of the study, in which the PIRAMID score was evaluated for its prognostic value regarding neurological symptomatology. The corresponding [15O]water PET data sets were available in 38 patients, of whom six patients had prior unilateral revascularization surgery. Accordingly, 140 ACA/MCA territories were evaluated in the second part of the study, in which the MARS-MMA scoring system was developed and compared to the PIRAMID scoring system for its capability to predict [15O]water PET impairment. Assessment of the Components of the PIRAMID/MARS-MMA Scoring System, Neurological Symptomatology and [15O]Water PET  
The frequencies of all components of the PIRAMID/MARS-MMA scoring systems (prior infarction on FLAIR/T2-weighted MRI, CVR impairment on bh-fMRI, arterial vessel wall contrast enhancement, Ivy sign, angiographic mSS and collateralization grading) and of neurological symptomatology and CPR impairment on [15O]water PET can be seen in Table 2. \begin{table}
\begin{tabular}{c c} \hline \hline Mean age (range) & 46 (15–75) \\ \hline Female–male ratio & 54:17 \\ \hline Imaging before revascularization & 61 \\ \hline Imaging after unilateral revascularization & 8 \\ \hline Structural MRI data sets & 69 \\ \hline Functional MRI data sets & 69 \\ \hline DSA data sets & 69 \\ \hline
[15O]water PET data sets & 38 \\ \hline Days between MRI and DSA data acquisition (mean \(\pm\) SD) & 11 \(\pm\) 25 \\ \hline Days between MRI and [15O]water PET data acquisition (mean \(\pm\) SD) & 50 \(\pm\) 36 \\ \hline Days between DSA and [15O]water PET data acquisition (mean \(\pm\) SD) & 53 \(\pm\) 34 \\ \hline \end{tabular}
\end{table} 
Table 1: General patient data. \begin{table}
\begin{tabular}{c c c} \hline \hline \multicolumn{1}{c}{
\begin{tabular}{c} **Analysis of the Territories of the** \\ **Internal Carotid Artery** \\ \end{tabular} } & \multicolumn{2}{c}{**Analysis of the Territories of the** \\ \hline Neurological symptomatology & 65/130 (50.0\%) & 83/260 (31.9\%) \\ \hline Motor deficit 1  & 30/130 (23.1\%) & 58/260 (22.3\%) \\ \hline Sensory deficit 1  & 59/130 (45.4\%) & 79/260 (30.4\%) \\ \hline Language deficit 1  & 24/64 (37.5\%) 2  & 24/64 (37.5\%) 2  \\ \hline Prior infarct & 67/130 (51.5\%) & 100/260 (38.5\%) \\ \hline Cerebrovascular reactivity impairment & & \\ \hline \(\geq\)10\% relative BOLD signal reduction & 115/130 (88.5\%) & 213/260 (81.9\%) \\ \hline \(\geq\)20\% relative BOLD signal reduction & 110/130 (84.6\%) & 191/260 (73.5\%) \\ \hline \(\geq\)30\% relative BOLD signal reduction & 104/130 (80.0\%) & 178/260 (68.5\%) \\ \hline \(\geq\)40\% relative BOLD signal reduction & 94/130 (72.3\%) & 158/260 (60.8\%) \\ \hline \(\geq\)50\% relative BOLD signal reduction & 81/130 (62.3\%) & 127/260 (48.8\%) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Clinical data. The visual inspection of the cerebellar signal time-courses showed the accurate performance of the bh-fMRI tasks in all patients, so no bh-fMRI data set had to be excluded from further analysis. The preliminary analysis to determine a bh-fMRI threshold value for further analysis revealed increasing sensitivity and decreasing specificity in predicting a severe CPR impairment with a rising CVR impairment (see Figure S1). A CVR impairment of 50% yielded the maximum Youden index, in both the analysis of the ICA territories (1.541) and the analysis of the ACA/MCA territories (1.567) (see Table S1). Therefore, a CVR impairment of \(\geq\)50% was used as a threshold to binarize the CVR. The preliminary analysis of the arterial wall contrast enhancement showed that a mild arterial wall contrast enhancement yielded the maximum Youden index of 1.302 (see