Espectroscopia de prótons por ressonância magnética: aplicação clínica em pacientes com lesões encefálicas focais

Abstract

Proton magnetic resonance spectroscopy is an noninvasive method that allows the detection of metabolic and biochemical detection of areas of the brain. This investigation focused on the clinical applications of proton MR spectroscopy in patients with focal brain lesions, considering the possibility of differentiate the normal brain tissue of pathological, neoplasic of non-neoplasic disorders, brain neoplasms to each other and similar lesions identified by the magnetic resonance imaging. A total of 308 proton magnetic resonance spectroscopies in 287 patients with focal brain lesions, 147 (51.2%) males and 140 (48.8%) females, was divided into three groups: Group I - 169 exams of patients with brain neoplasic; Group II - 58 exams of patients with non-neoplasic focal brain lesions, and Group III - 32 exams of individuals without lesions. Single voxel proton MR spectroscopy with echo time 136 ms was the method used. The qualitative analysis of the peaks of metabolites N-acetyl aspartate (Naa - 2,0 ppm), creatine (Cr - 3,0 ppm) and choline (Cho - 3,2ppm), expressed in graph, and quantitative by means of the calculation of the ratios Naa/Cr, Co/Cr and Co/Naa through height measurement of the peaks in the graph. The statistical analysis included Kruskal-Wallis test and principal component analysis. In most of spectroscopies performed in patients of Group I, there was an accentuated increase of Cho peak and reduction of Naa; in Group II slight increase of Cho and decrease of Naa was observed, while in the individuals of Group III Naa was the larger peak, corresponding to the double of the height of the Cho and Cr peaks. Lipids (0.9 and 1.3 ppm), that generally indicate necrosis, was detected more usually in malignant neoplasms (multiforme glioblastoma and metastases) and inflammatory process by toxoplasmosis. Aminoacids (0.9 ppm inverted) were detected only in pyogenic abscesses. Median values of Naa/Cr, Co/Cr and Cho/Naa ratios in Group I were 0.75, 3.00, and 4.00; 1.13, 1.20, and 0.92 in Group II; and 2.00, 0.76, and 0.40 in group III, respectively. With the ratios studied, it was possible differentiate significantly the three groups (p<0.001). The clinical application of the proton MR spectroscopy is useful to the elucidation of the etiological diagnosis of focal brain lesions. Metabolic pattern obtained by proton spectroscopy is distinct between normal brain tissue and pathological, occurring significant difference between neoplasic of non-neoplasic disorders. Proton magnetic resonance spectroscopy contribute to differentiate focal brain lesions similar to the magnetic resonance imaging exam.