LOCALIZED PROTON SPECTROSCOPY OF FOCAL BRAIN PATHOLOGY IN HUMANS - SIGNIFICANT EFFECTS OF EDEMA ON SPIN-SPIN RELAXATION-TIME

Localized proton nuclear magnetic resonance (NMR) spectroscopy of huma n brain in two common focal pathologies producing brain edema (peritum or edema and acute edematous ischemic stroke) was performed utilizing point resolved spectroscopy (PRESS). The spectra obtained from the pat hological tissues were characterized by a reduced N-acetyl-aspartate, (NAA) to total creatine (Cr) ratio (NAA/Cr) and high level of lactate. While the spin lattice relaxation time (T-1) of the main metabolite r esonances, namely, those of NAA, Cr, and choline containing compounds (Cho), showed values similar to those of normal brain, the spin-spin r elaxation time (T-2) of these metabolites exhibited a dramatic shorten ing in pathological tissues. Serial postoperative measurements of T-2 in two patients with peritumor edema showed a gradual recovery of the T-2 shortening corresponding to improvement of the edema. The majority of localized spectroscopy studies in humans is performed using a sequ ence which utilizes spin echo signals with a fined single echo time. H ence, the signal intensities of the metabolite resonances obtained are inherently T-2 dependent. The current study underscores that cautious interpretation of clinical data with respect to metabolite quantifica tion is warranted.