A 58-year-old man with a 10-year history of hypertension (BP 160/100 mmHg on presentation) presents to the emergency department with acute onset severe headache, vomiting, and left-sided weakness. Non-contrast CT head performed 2 hours after symptom onset shows a 4 cm hyperdense lesion in the right basal ganglia with surrounding hypodensity. There is midline shift of 8 mm. What is the most appropriate next imaging modality to assess the extent of hemorrhage and guide management?