Usefulness of short TE proton MR spectroscopy in grading brain glial tumors

To determine the usefulness of in-vivo proton MR spectroscopy (MRS) with short TE for grading glial brain tumors. For the purpose of tumor grading, 32 patients with pathologically confirmed glial tumors were examined by proton MRS. This and MRI were performed on a 1.5T superconductive MR scanner. T2-weighted FSE images (TR/TE=3D4000/100 msec) were used to obtain anatomical reference images. The stimulated-echo acquisition mode (STEAM:TR/TE/MT=3D3000/30/13.7 msec) was used to acquire MRS data from the localized single-voxel (2x2x2 cm3) in both hemispheres. Residual water resonance in the spectra was removed using a CHESS pulse sequence. Prior to baseline correction, MRS raw-data, free induction decay signals were zero-filled, apodized by an exponential function with 8 Hz line-broadening, and fourier transformed. To normalize signal intensities of metabolites such as N-acetyl aspartate (NAA), total chloline (Cho), myo-inositol ml), and lactate (Lac), the creatine (Cr) peak was used as a standard. The concentration ratios of Cho/Cr, mI/Cr, α-Glx, Lac, and NAA/Cr changed lineaarly according to tumor grade. Increased Cho, mI, αGIx, and Lac levels were clearly seen in all grades. The most dramatic increases, observed in either Grade III or IV, were 78% and 228% for Cho (p less than 0.001), 106% and 61% for mI (p less than 0.001), 32% and 5% for α-Glx, and 727% and 450% for Lac (p less than 0.001), respectively. Increase of concentration ratio of Lac/Cr observed only in Grade III and Grade IV. The concentration ratios of NAA/Cr decreased gradually as tumor grade increased (p less than 0.001). The metabolic changes seen on proton MR spectroscopy using short TE might be useful for grading glial brain tumors. (author)