177 Physiological MRI Biomarkers & Cognition after SRS for Brain Metastases least one task within that domain showed improvement, as declined if at least one task showed a decline, as mixed if at least one task indicated improvement and one task indicated decline and as stable when all tasks within that domain showed stable performance. Figure 1. Data analysis steps for the MRI data. MRI analysis was performed for the BOLD, ASL and QSM data. 1) CVR maps were generated with the SeeVR toolbox using the BOLD time series and PetCO2 traces, quantitative CBF maps were generated based on the multi-delay ASL data using the ClinicalASL toolbox and FSL BASIL, and OEF maps were generated from the QSM data with the QQ-CTV software package. 2) All MRI maps were transformed to the baseline T1 patient space. 3) The CMRO2 map was generated by multiplying the CBF map with the OEF map. Multiple masks were generated. Edema masks were made based on the T2FLAIR hyper intensities for both baseline (T0) and follow-up (T1). From this, new masks including regions only exhibiting edema at baseline (edema T0), regions only exhibiting edema at follow-up (edema T1) and regions exhibiting edema at both time-points (edema T0+T1) were created. The brain metastases were excluded from the edema regions. Next, the edema and brain metastases mask were excluded from the whole-brain mask to create a mask with healthy appearing brain tissue at both time points. This healthy appearing brain tissue was subdivided into grey matter (GM) and white matter (WM). Difference maps subtracting the follow-up (T1) data from the (T0) were calculated for CVR and CMRO2. Positive values represent an increase in either CVR or CMRO2 at follow-up (T0<T1) and negative values represent a decrease in either CVR or CMRO2 at follow-up (T0>T1). The subtraction process was restricted to pixels that contained values in both the pre- and post-radiotherapy images. Images were masked to exclude CSF. Finally, dose maps were extracted with one map showing the total delivered dose in EQD2 and the other map dividing the dose into ROIs with low (<10 Gy), medium (10-15 Gy) and high (>15 Gy) dose, as described above. 7
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