The presence of cerebral vasospasm identified with transcranial Doppler, digital subtraction angiography, or CT angiography (CTA) is frequently used to confirm DCI. Presence of vasospasm, however, does not prove the presence of ischemia and absence of vasospasm does not rule out. Better diagnostic tests in the acute stage of deterioration, possibly caused by DCI, are therefore needed. In patients with SAH, CTP has recently been shown to be promising for detection of early ischemia.