Radiation-induced changes in human brain metabolites as studied by 1H nuclear magnetic resonance spectroscopy in vivo

Abstract

Purpose : External radiation therapy for brain tumors exposes healthy areas of brain to considerable doses of radiation. This may cause cognitive and psychological impairment, which indicate neuronl dysfunction. 1H-magnetic resonance spectroscopy (MRS) was used to study brain metabolites in the adjacent regions 0.5–13 years after exposure to the thereapeutic irradiation. Methods and Materials : Eigth patients with irradaited brain tumors were examined by means of in vivo 1H-MRS using a point-resolved spectroscopy (PRESS) sequence with echo times of 60 or 270 ms. The metabolites were quantified by using brain water concentrations as internal reference. The volume of interest (VOI) was positioned in irradiated brain areas excluding, however, scar and recurrent tunors. The respectiv radiation doses were measured based on radiation therapy plans, simulator films, and localization MR images. Results : The concentration of the neuron-specific metabolite N-acetyl- L-aspartate (NAA) was 13.2 ± 1.4 mmol/I in controls, where it was reduced in the brain of treated patients to 8.6 ± 0.9 mmol/I (total radiation those 59–62 Gy). Concentrations of cratine and choline-containing compounds were unchanged. The T2 of water was longer in irradiated than in unexposed brain areas. Conclusions : Therapeutic brain irradiation causes neuronal damage, which is reflected by reduction of N-acetyl- l-aspartate (NAA) concentrations. 1H-MRS could serve clinically as a means of evaluating adverse effects in the central nervous system, enabling intervention and rehabilitation.