Functional MRI please help A2 Biology help

Watch this thread
Leah.J
Badges: 13
Rep:
? You'll earn badges for being active around the site. Rep gems come when your posts are rated by other community members.
#1
Report Thread starter 2 years ago
#1
In fMRI's , according to the MS, the area with the lowest signal has the highest brain activity, but at the same time, they are the areas that "light up" in a scan.
So, I'm a bit confused, how can these 2 go together ? or what does a fMRI measure ?
High brain activity= a lot of O2 = little radio waves absorbed
The signal is weak but the area lights up .. how ?
0
reply
Jpw1097
Badges: 19
Rep:
? You'll earn badges for being active around the site. Rep gems come when your posts are rated by other community members.
#2
Report 2 years ago
#2
(Original post by Leah.J)
In fMRI's , according to the MS, the area with the lowest signal has the highest brain activity, but at the same time, they are the areas that "light up" in a scan.
So, I'm a bit confused, how can these 2 go together ? or what does a fMRI measure ?
High brain activity= a lot of O2 = little radio waves absorbed
The signal is weak but the area lights up .. how ?
fMRI works on the principle that deoxyhaemoglobin is magnetic (paramagnetic) and oxyhaemoglobin virtually isn't (diamagnetic). When a particular region of the brain becomes active, the neurones become more metabolically active and so the blood flow to that region increases, bringing with it more oxyhaemoglobin - displacing deoxyhaemoglobin. This essentially 'changes' the signal and this is picked up on scans - I'm pretty sure this is all you'd need to known.
I'm not an expert on how MRI works (although I did cover medical imaging in A level physics) but it's something like this: a magnetic field is applied and protons within water molecules align so that they are in line with the magnetic field. A radio frequency pulse is fired causing the protons to flip out of alignment; these protons then flip back into alignment and in doing so, they release radiowaves at the same frequency as the pulse that flipped them, and these radiowaves are detected. The time taken for the protons to return to their original position depends on the surrounding tissue. Given that there are multiple coils generating multiple magnetic fields within the scanner, each location in the scanner has a different radiofrequency pulse needed to flip the protons - therefore, when the detector detects a particular radio frequency, it knows the exact location of where it came from.
I suppose if oxyhaemoglobin is resistant to magnetism, it would not align with the field and so would not absorb or emit radiowaves, whereas deoxyHb would. Since you want the active brain regions to light up, I can't imagine it would be difficult - you would just flip the image so that the low signal areas light up and high signal areas do not.
0
reply
X

Quick Reply

Attached files
Write a reply...
Reply
new posts
Back
to top
Latest
My Feed

See more of what you like on
The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

Personalise

How did the exam go for you?

Great! (9)
16.36%
Quite well (24)
43.64%
Not so good (13)
23.64%
Terrible! (9)
16.36%

Watched Threads

View All