Fig. 1. The panels depict the need for a computational approach to measure proximal-conductance and distal-arteriolar resistances as well as the experimental protocol. (A ) The outline shows the isolation of the segment of the conductive artery between the coaxial guiding catheter in the internal carotid artery and microcatheter in the middle cerebral artery (MCA ), across which proximal-conductive arterial resistance can be measured without obstructing flow. (B ) Lateral view of the 133Xe detectors and transcranial Doppler (TCD) probe placements that monitor total cerebral perfusion and blood flow velocity in the MCA, respectively. (C ) Frontal view of the placement of the same detectors. (D ) Digital subtraction angiogram showing injection of the dye through the microcatheter shows that segments of proximal-conductance arteries lie distal to the microcatheter. A computational approach enables assessment of the resistance of the segment of the proximal conductance artery shown in C , across which resistance cannot be measured by advancing the catheter, as it is likely to obstruct flow.