- Vasospasm following aneurysmal subarachnoid hemorrhage is ascribed to be the cause of morbidity and mortality in 10-30% of patients. Vascular narrowing following SAH defined by angiography (along with non-invasive vascular imaging such as CT angiography) is, however, present in most patients. We seek to describe the need for understanding the clinically relevant syndrome of delayed ischemic neurological deficit (DIND) and to describe various perfusion techniques which in addition to vascular imaging studies, are needed to fully understand when delayed neurological deficits are due to due vasospasm induced ischemia.The literature regarding various perfusion techniques as they relate to vasospasm and DIND was reviewed.There are many techniques which offer some data regarding cerebral blood flow in the setting of DIND. Truly quantitative techniques such as positron emission tomography and xenon CT offer powerful tools to identify areas at increased risk for infarction. Xenon CT is a practical technique which may be performed at the bedside and may be used to assess cerebral blood flow response to a changing variable.Perfusion techniques offer clinical data which may be applied to the care of an individual patient so that treatment may be tailored to that patient's physiological needs. This allows the clinician to pursue a rational strategy for diagnosis and treatment of a patient with a delayed neurological deficit following aneurysmal SAH.