Abstract
MRI and MRS are established methodologies for evaluating intracranial lesions. One MR spectral feature suggested for in vivo grading of astrocytic tumours is the apparent myo-lnositol (ml) intensity (ca 3.55 ppm) at short echo times, although glycine (gly) may also contribute in vivo to this resonance. The purpose of this study was to quantitatively evaluate the ml + gly contribution to the recorded spectral pattern in vivo and correlate it with in vitro data obtained from perchloric acid extraction of tumour biopsies. Patient spectra (n = 95) at 1.5T at short (20-31 ms) and long (135-136 ms) echo times were obtained from the INTERPRET MRS database (http://gabrmn.uab.eslinterpretvalidateddbl). Phantom spectra were acquired with a comparable protocol. Spectra were automatically processed and the ratios of the (ml + gly) to Cr peak heights ((ml + gly)/Cr) calculated. Perchloric acid extracts of brain tumour biopsies were analysed by high-resolution NMR at 9.4T. The ratio (ml + gly)/Cr decreased significantly with astrocytic grade in vivo between low-grade astrocytoma (A2) and glioblastoma multiforme (GBM). In vitro results displayed a somewhat different tendency, with anaplastic astrocytomas having significantly higher (ml + gly)/Cr than A2 and GBM. The discrepancy between in vivo and in vitro data suggests that the NMR visibility of glycine in glial brain tumours is restricted in vivo.
Highlights
A2 A3 GBM mI Gly Cr NAA Cho SW TR TE short TE (STE) long TE (LTE) Perchloric acid (PCA) HR-MAS wtw
We report the use of a simple expression for mI + gly content relative to creatine content for astrocytic tumour grading from in vivo MRS data, and an investigation of a biochemical rationale for this method, based on the analysis of biopsy metabolite extracts by high field NMR spectroscopy
The mI signal at LTE was attenuated when compared to the creatine signal, due to mI J-coupling induced phase modulation, whereas glycine remained practically isointense with respect to creatine at 3.03 ppm (Fig. 1)
Summary
Low-grade astrocytoma Anaplastic astrocytoma Glioblastoma Multiforme Myo-inositol Glycine Creatine N-acetyl aspartate Choline Sweep width Recycling time Echo time Short time of echo Long time of echo Perchloric acid High resolution magic angle spinning Wet tissue weight. MRI and MRS are well established methodologies for evaluating intracranial lesions [1,2]. MRS of brain tumours is currently used for diagnosis, grading, assessing therapeutic response and providing prognostic information on survival [3,4]. Chamberlain and Kormanik [6] have reported percentages of 4050% for glioblastomas (GBM), 3035% for anaplastic astrocytomas (A3), and 15-20% for low grade astrocytoma (A2). Current radiological methods do not distinguish adequately between the large number of recognised types of brain tumours, and histopathological diagnosis from a biopsy remains the gold standard for diagnosis and grading,
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