Necrotic tumor versus brain abscess: Importance of amino acids detected atH-1 MR spectroscopy - Initial results

PURPOSE: To assess the usefulness of the 0.9-ppm peak from amino acids (-CH 3 moieties from valine, leucine, and isoleucine) for the differentiation of brain abscesses and tumors at in vivo hydrogen 1 magnetic resonance (MR) s pectroscopy. MATERIALS AND METHODS: Amino acid concentrations were determined in vitro i n 13 purulent samples from brain and nonbrain tissues and in nine aseptic f luids from necrotic brain tumors at two-dimensional (2D) H-1 MR spectroscop y and liquid Thirty-four patients with cystic intracerebral mass lesions (2 8 tumors, six abscesses) were examined at H-1 MR spectroscopy in vivo. RESULTS: Amino acids were identified in vitro in both purulent and aseptic samples. Amino acid concentrations measured in the aseptic fluids at both l iquid chromatography and 20 MR spectroscopy were far below the detection th reshold of in vivo H-1 MR spectroscopy. Quantitative results obtained at 2D MR spectroscopy showed no :overlap in the ranges of amino acid concentrati ons in purulent and aseptic samples. In vivo, the proton spectra obtained w ith a 136-msec echo time (TE) revealed amino acids. (inverted peak at 0.9 p pm) in only the abscesses. CONCLUSION: The detection of amino acid resonance at 0.9 ppm at in vivo H-1 MR spectroscopy (136-msec TE) is a promising tool for distinguishing bacte rial abscesses and cystic brain tumors.