Editing Magnetic resonance imaging (section)

==== Angiography ====
[[File:mra1.jpg|thumb|Magnetic resonance angiography]]
{{Main|Magnetic resonance angiography}}

Magnetic resonance [[angiography]] (MRA) generates pictures of the arteries to evaluate them for [[stenosis]] (abnormal narrowing) or [[aneurysm]]s (vessel wall dilatations, at risk of rupture). MRA is often used to evaluate the arteries of the neck and brain, the thoracic and abdominal aorta, the renal arteries, and the legs (called a "run-off"). A variety of techniques can be used to generate the pictures, such as administration of a [[paramagnetic]] contrast agent ([[gadolinium]]) or using a technique known as "flow-related enhancement" (e.g., 2D and 3D time-of-flight sequences), where most of the signal on an image is due to blood that recently moved into that plane (see also [[FLASH MRI]]).<ref name="Wheaton Miyazaki pp. 286–304">{{cite journal | vauthors = Wheaton AJ, Miyazaki M | title = Non-contrast enhanced MR angiography: physical principles | journal = Journal of Magnetic Resonance Imaging | volume = 36 | issue = 2 | pages = 286–304 | date = August 2012 | pmid = 22807222 | doi = 10.1002/jmri.23641 | publisher = Wiley | s2cid = 24048799 | doi-access = free }}</ref>

Techniques involving phase accumulation (known as phase contrast angiography) can also be used to generate flow velocity maps easily and accurately. Magnetic resonance venography (MRV) is a similar procedure that is used to image veins. In this method, the tissue is now excited inferiorly, while the signal is gathered in the plane immediately superior to the excitation plane—thus imaging the venous blood that recently moved from the excited plane.<ref name="haacke">{{cite book | vauthors = Haacke EM, Brown RF, Thompson M, Venkatesan R |title=Magnetic resonance imaging: Physical principles and sequence design |publisher=J. Wiley & Sons |location=New York |date=1999 |isbn=978-0-471-35128-3 }}{{page needed|date=July 2013}}</ref>

{{anchor|Contrast agents}}