I printed this paper and I'm going to take a look at it this weekend. I'll let you know what I think.
In general, there are some interesting ways to determine the composition of a tissue on an MRI with some of these techniques.
MRI Spectroscopy has some metabolites that can be used:
NAA - marker for neuronal viability, found in high concentrations in neurons, and reduced by any process that destroys neurons
Creatine - found in metabolically active tissue, reduced in gliomas
Choline - marker of cellular membrane turnover, elevated in neoplasms, demyelination, and gliosis. In Gliomas, elevation of choline beyond margins of contrast demonstrate cellular infiltration of tumor
Lactate - marker of anaerobic metabolism and is therefore elevated in necrotic areas, higher grade tumors
A recurrence on an MRI Spectroscopy would show: increased choline, decreased creatine, and the Choline/NAA ratio would be >2.
Radiation necrosis would have increased lactate and decreased choline, creatine, and NAA
Perfusion weighted MRIs can be helpful too. It can estimate the microvascular density (MVD) by measuring the cerebral blood volume. Radiation therapy leads to endothelial cell damage and small vessel injury, so there is reduced perfusion and reduced MVD. Tumor recurrence promotes angiogenesis (making new blood vessels) and thus increases MVD