MR of Hemorrhage

Be familiar with the MR appearance of hemorrhage.

http://emedicine.medscape.com/article/344973-overview

Q: What blood product is bright on T1?

A: Methemoglobin

Q: Intra or extracellular Methemoglobin?

A: Both (they are only different on T2)

Q: How does an understanding of the MR of hemorrhage help one understand fMRI?

A: Metabolically active brain consumes oxygen. Autoregulatory mechanisms overcompensate with increased flow, leading to paradoxically increased oxyhemoglobin/decreased deoxyhemoglobin which cause increased signal. Therefore the active brain will be brighter. This is the basis of BOLD (blood oxygen level dependent) fMRI.