Editing Perfusion (section)

===Magnetic resonance imaging===
{{main|Magnetic resonance imaging}}
Two main categories of magnetic resonance imaging (MRI) techniques can be used to measure tissue perfusion [[in vivo]].
* The first is based on the use of an injected [[contrast agent]] that changes the [[magnetic susceptibility]] of blood and thereby the MR signal which is repeatedly measured during [[Bolus (medicine)|bolus]] passage.<ref>Huettel, S. A.; Song, A. W.; McCarthy, G. (2009), Functional Magnetic Resonance Imaging (2 ed.), Massachusetts: Sinauer, {{ISBN|978-0-87893-286-3}}</ref> 
* The other category is based on [[arterial spin labelling]] (ASL), where arterial blood is [[magnet]]ically tagged before it enters into the tissue being examined and the amount of labelling that is measured and compared to a control recording obtained without spin labelling.<ref>{{Cite journal|title = Applications of arterial spin labeled MRI in the brain|journal = Journal of Magnetic Resonance Imaging|date = 2012-05-01|issn = 1522-2586|pmc = 3326188|pmid = 22246782|pages = 1026–1037|volume = 35|issue = 5|doi = 10.1002/jmri.23581|first1 = John A.|last1 = Detre|first2 = Hengyi|last2 = Rao|first3 = Danny J. J.|last3 = Wang|first4 = Yu Fen|last4 = Chen|first5 = Ze|last5 = Wang}}</ref>