Hi Liz,

Are we talking about "functional MRI" or "standard MRI"? My understanding is that standard MRI will provide anatomic information not significantly different from the CT scan I already had. Like a CT scan, I think standard MRI cannot distinguish between necrotic tissue, edematous tissue, and cancerous tissue. I think a PET/CT can distinguish between necrotic tissue on the one hand, and either edematous or cancerous tissue on the other hand. Thus, a negative PET/CT reliably indicates only necrotic tissue is present while a positive PET/CT indicates that either edematous or cancerous tissue is present.

My understanding is that a CT scan merely tells the doctors there is an abnormal lump of tissue present and does not distinguish the state of this tissue (necrotic or edematous or cancerous)... its based on how well this soft tissue blocks x-rays and I think it blocks x-rays about equally well regardless of the state.

My understanding is that the standard MRI provides similar information... but its based on the density of hydrogen atoms in the tissue (many of these hydrogen atoms belong to larger molecules) with a higher density providing a stronger MRI response. Perhaps there is some difference in hydrogen density between necrotic tissue on the one hand and either edematous or cancerous tissue on the other hand... in which case the standard MRI might provide similar information to a PET/CT... but its my impression that, in order for a standard MRI to reduce the "false positives" problem of a PET/CT, there would have to be a detectable difference in hydrogen density between edematous tissue and cancerous tissue. While I suppose such a difference in hydrogen density might exist, I don't know enough to know for sure that it does... my "wild guess" is that any such differences are small and would be an unreliable means to distinguish these two kinds of soft tissue.

But I'd also make a "wild guess" that its theoretically possible to design a specialized "functional MRI" scan (which focuses on something other than simple hydrogen density) to reliably distinguish these two kinds of soft tissue - whether anyone has tried to design such a specialized MRI scan (and whether its gone beyond a research exploration to reach clinical practice) I do not know.

Does anyone know what an MRI can do that a CT scan or a PET/CT cannot do?

Rob