Editing Haemodynamic response (section)

===PET scan===

PET scan or [[Positron emission tomography scan]] is also used alongside fMRI for brain imaging. PET scan can detect active brain areas either haemodynamically or metabolically through glucose intake. They allow one to observe blood flow or metabolism in any part of the brain.  The areas that are activated by increased blood flow and/or increased glucose intake are visualized in increased signal in the PET image.<ref>"Learn More About Brain Imaging Technologies." Learn More About Brain Imaging Technologies. N.p., n.d. Web. 03 Nov. 2012. <http://learn.genetics.utah.edu/content/addiction/drugs/brainimage.html {{Webarchive|url=https://web.archive.org/web/20130121151218/http://learn.genetics.utah.edu/content/addiction/drugs/brainimage.html |date=2013-01-21 }}></ref>

Before a PET scan begins, the patient will be injected with a small dose of a radioactive medicine tagged to a [[Radioactive tracer|tracer]] such as glucose or oxygen. Therefore, if the purpose of the PET scan is to determine brain activity, [[Fludeoxyglucose (18F)|FDG]] or [[fluorodeoxyglucose]] will be the medicine used. FDG is a complex of radioactive fluorine that is tagged with glucose. If a certain part of the brain is more active, more glucose or energy will be needed there and more FDG will be absorbed. This increase in glucose intake will be detectable with increased signal in the PET image. PET scanners provide this feature because they measure the energy that is emitted when [[positrons]] from the [[radiotracer]] collide with electrons in the brain. As a radiotracer is broken down, more positrons are made and there will be an increased signal in the PET scan.<ref>Shibasaki, Hiroshi. "Human Brain Mapping: Hemodynamic Response and Electrophysiology." Elsevier. N.p., n.d. Web. <http://moodle.technion.ac.il/pluginfile.php/195507/mod_resource/content/0/week1/FunctionalBrainImaging.pdf></ref>