LOCALIZED PROTON SPECTROSCOPY AND SPECTROSCOPIC IMAGING IN CEREBRAL GLIOMAS, WITH COMPARISON TO POSITRON EMISSION TOMOGRAPHY

In 32 patients with gliomas, one- and two-dimensional proton magnetic resonance spectroscopy (H-1-MRS) has been conducted, the latter allowi ng reconstruction of spectroscopic data into a spectroscopic image (MR SI), showing the distribution of the various metabolite concentrations over the cross-sectional plane. For lack of absolute concentrations, the measured concentrations of phosphocholine (CHOL), N-acetyl-L-aspar tate (NAA), and lactate (LAG) were conventionally expressed in ratios relative to that of creatine (CREAT). Compared to normal brain tissue, an increased CHOL/CREAT ratio was found in all groups of tumours, in glioblastomas, high-, middle- and low-grade astrocytomas both at the m argin and the core of the tumours, but in oligodendrogliomas only at t he margin. This is consistent with an increased phosphocholine turnove r in relation to membrane biosynthesis by the proliferating cells. The NAA/CREAT ratio was decreased in all groups of tumours, both in the c entre and at the margin, reflecting replacement of functioning neurons by neoplastic cells. The LAG/CREAT ratio was elevated in the core of malignant gliomas, which may be the result of a prevailing glycolysis, characteristic of tumours, possibly in conjunction with hypoxia/ischa emia. In the perifocal oedema, there was neither elevation of the CHOL /CREAT ratio nor decrease of the NAA/CREAT ratio; an increased LAC/CRE AT ratio therefore rather reflected ischaemia/hypoxia probably due to locally elevated pressure and compromised regional perfusion. In the n ormal brain, the metabolite ratios of grey matter did not differ from those of white matter. The frontal lobe and basal ganglia showed lower NAA/CREAT ratios than the other cerebral areas. In 7 patients positro n emission tomography was also performed with [F-18] fluoro-2-deoxy-D- glucose ((18)FDG) or L-[1-C-11]-tyrosine (C-11-TYR); the latter demons trated a pattern of C-11-TYR uptake similar to that of CHOL elevation in the MRSI.