Ask Your Health Question and Get an Answer ASAP
This is Dr. David
an MRI scan uses a strong magnetic field to align up atoms and then hits them with a radiofrequency pulse and the atoms get knocked off their axis and then come back to magnetic north. when they do this, they give off signals for the MRI machine to pick up on to make the image of your brain.
blood in blood vessels flow during this process
so by the time the radiofrequency pulse his the area, the atoms in the blood which were aligned up to magnetic north have already flowed out of the MRI image field. that is why there is a flow void seen in vein blood vessels on MRI scans of the brain. a flow void is really a normal finding on an MRI scan.
let me know if you have other questions.