Posted by SLS on November 24, 2004, at 11:20:03
In reply to Scans, Pet, Spect and fMRIs?, posted by denise1904 on November 24, 2004, at 8:08:43
Hi Denise.
I'm not sure about all of this, but I'll take a shot at it.
A regular MRI resolves brain structures, mapping the gross topology of the brain. The images display the brain as it exists in one moment of time. If you are "missing" significant amounts of brain tissue, it should show up in the image. However, I don't think a MRI can resolve smaller brain circuits, even though significant numbers of neurons might be absent. For now, neurons at this level are best determined by their activity, which requires dynamic measurements.
SPECT and fMRI rely on the measurement of blood flow to produce an image. Blood flow is an index of neural activity as the active neurons require more oxygen and thus more blood. PET, on the other hand, is an index of molecular binding or metabolism. It can determine the activity of neuronal tissue by measuring the uptake of radiolabelled glucose (flouroxydeoxyglucose). Using other types of radiolabelled molecules known to be ligands of specific receptors, PET can determine the density and location of those receptord. PET can produce images of greater resolution than SPECT, but is very much more expensive to implement.
MRI - density of water in tissues
fMRI - density of water molecules in oxygenated blood within the blood stream.
SPECT - density of radioactive decay of tracer elements within the blood streem.
PET - density of radiolabelled glucose molecules accumulated in within neurons.
- Scott
poster:SLS
thread:419673
URL: http://www.dr-bob.org/babble/20041123/msgs/419734.html