Arterial Spin Labeled Perfusion MRI

Perfusion refers to the delivery of oxygen and nutrients to tissues by means of blood flow and is one of the most fundamental physiological parameters. Disorders of perfusion also account for most of the leading causes of medical disability and mortality. While measurements of perfusion are of direct diagnostic value in vascular disorders, perfusion measurements also serve as biomarkers for a broader range of physiological and pathophysiological functions. A close coupling between cerebral blood flow and metabolism allows regional brain function to be assessed through measurements of cerebral perfusion and increased vascularity of neoplasms allows tumor perfusion to be used as a measure of tumor grade and to monitor the response to tumor therapy. Classical tissue perfusion is measured using a diffusible tracer that can exchange between the vascular compartment and tissue. This yields a perfusion measurement in units of milliliters of blood flow per gram of tissue per unit time (ml/g/ min). However, owing to the relative ease of inferring hemodynamic function from the passage of an intravascular tracer, the term “perfusion imaging” has also been applied to measurements of perfusionrelated parameters such as mean transit time and blood volume that can be related to perfusion through the Central Volume Principle. In the field of MRI, most people associate the concept of perfusion imaging with dynamic susceptibility contrast imaging using a relaxation contrast agent. However, there are also several methods for the measurement of classical Arterial Spin Labeled Perfusion MRI