151 Hemodynamic Imaging in Brain Metastases: ASL vs. Hypercapnic BOLD Figure 1. CO2 breathing trace of a representative subject during the breathing challenge. The blue line indicates the actual measured PetCO2 values, while the red line indicates the desired values based on the protocol. Abbreviations: PetCO2, end-tidal CO2. BOLD data was motion corrected (MCFLIRT)22, corrected for geometric distortion using TOPUP26,27 and linear spatial co-registered to the T1 image using the ‘epi_reg’ function.22,25 The T1w segmentation masks, edema masks and gross tumor volume masks were translated to the functional (i.e. BOLD) space using the inverse of the matrices output by epi_reg. For the ASL data, the reconstructed T1 (M0) was spatially registered to the pre-TOPUP mean BOLD image. The resulting transformation matrix as well as the distortion-correction fields were then applied to the ASL images in order to move them to functional patient space. Data analysis MRI analysis The pipeline to process and compare the BOLD and ASL data is visually depicted in Figure 2. CVR and hemodynamic lag maps were derived using the open-source seeVR toolbox (available at https://www.seevr.nl/).28 In brief, in order to remove signal contribution from large veins that might overshadow tissue responses, a 6
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