IDENTIFICATION AND QUANTITATION OF PHENYLALANINE IN THE BRAIN OF PATIENTS WITH PHENYLKETONURIA BY MEANS OF LOCALIZED IN-VIVO H-1 MAGNETIC-RESONANCE SPECTROSCOPY

Localized proton MR spectroscopy was used to identify phenylalanine (P HE) and to quantitate its cerebral concentration in patients with type I phenylketonuria (PKU). Data acquisition was optimized for the detec tion of low-concentration metabolites, using a short TE (20 ms) double Hahn-echo localization sequence for large volumes within the head coi l and for smaller volumes using a surface coil, Previously described m ethods to quantitate localized MR spectra were extended to cover the c ase of low-concentration metabolites, unevenly distributed in three br ain compartments and measured in difference spectra only. PHE content was determined in difference spectra of four PKU patients with respect to normals and in one patient before and after an oral load of L-PHE, PHE concentrations of 0.3 to 0.6 mmol/kg brain tissue were obtained, resulting in a concentration gradient for PHE between blood and brain tissue of 2.4 to 3.0, No significant changes were found for the abunda nt metabolites in gray or white matter. Previously reported MRI change s were confirmed to be due to increased cerebro-spinal-fluid-like spac es. (C) 1995 Academic Press, Inc.