Various diagnostic tools are commonly used to identify (1) arterial narrowing and/or (2) perfusion abnormal- ities or reduced brain oxygenation. These different tools have advantages and disadvantages. Although comparative studies of diagnostic accuracy for large arterial narrowing have been performed for some modalities, no randomized trials have compared the impact of the use of different diagnostic methods on patient outcomes. That said, there are emerging data that perfusion imaging, demonstrating regions of hypo- perfusion, may be more accurate for identification of DCI than anatomic imaging of arterial narrowing or changes in blood flow velocity by transcranial Doppler, for which the data are best for the middle cerebral artery territory.224 226 Perfusion CT is a promising technology, although repeat measurements are limited by the risks of dye load and When DCI is diagnosed, the initial treatment is the induc- tion of hemodynamic augmentation to improve cerebral perfusion. No randomized trials of this intervention have been performed, but the rapid improvement of many patients with this therapy and their worsening when it is stopped prema- turely are convincing proof of efficacy. The exact mechanism of benefit is unclear. In some patients, increased mean arterial pressures may increase cerebral blood flow in the setting of autoregulatory dysfunction. In others, there may be some direct transluminal pressure effect that leads to arterial dilation.227 Traditionally, hemodynamic augmentation has consisted of he- modilution (a common occurrence in this population), hypervol- emia, and hypertensive therapy. 