Editing Perfusion (section)

===Microspheres===
{{main|Microspheres}}
Microspheres that are labeled with [[radioactive isotopes]] have been widely used to measure perfusion since the 1960s. Radioactively labeled particles are injected into the test subject and a [[radiation detector]] measures radioactivity in tissues of interest.<ref name=Wagner>Studies of the Circulation with Radioactive Microspheres., Wagner et al, Invest. Radiol., 1969. 4(6): pp. 374–86.</ref> Microspheres are used in [[radionuclide angiography]], a method of diagnosing heart problems.

In the 1990s, methods for using [[fluorescent]] microspheres became a common substitute for radioactive particles.<ref name=OnlineGlenny>{{cite web|title=Fluorescent Microspheres|url=http://fmrc.pulmcc.washington.edu/DOCUMENTS/FMRCMAN99.pdf|publisher=[[Fluorescent Microsphere Resource Center]]|url-status=dead|archive-url=https://web.archive.org/web/20121002175850/http://fmrc.pulmcc.washington.edu/DOCUMENTS/FMRCMAN99.pdf|archive-date=2012-10-02}}</ref>