Proton chemical shift imaging, metabolic maps, and single voxel spectroscopy of glial brain tumors

Abstract

Seventeen patients with presumed glial brain tumors were examined with proton chemical shift imaging and single voxel spectroscopy that used different echo times. Metabolite resonances were evaluated by metabolic ratios and absolutely by correcting for coil load and comparison to phantom measurements. Metabolic images were created to visualize the metabolic changes. All patients showed spectra that were different from those measured in healthy control subjects. Spectral changes were also present in normal-appearing matter (NAM) that was distant from lesions. The resonance at 3.55 ppm which is usually assigned to both myo-inositol and glycine, was the only one to allow a discrimination between healthy volunteers, astrocytoma grade II, and glioblastoma multiforme (GBM) (p < 0.02). From the different echo times used we conclude that an increase in this resonance has to be assigned to glycine rather than myo-inositol. This resonance might be used to grade human gliomas more reliably. Total creatine (Cr) decreased more drastically with malignancy than N-acetylated metabolites (NA). This led to a higher NA/Cr ratio in GBM compared to astrocytoma grade II. NA/Cr was thus pseudonormal in GBM due to a change in both nominator and denominator. This study reveals the importance of comparing magnetic resonance spectroscopy data of lesions to spectra measured in identical localizations in healthy control subjects instead of NAM and the importance of quantifying single metabolic peaks instead of creating metabolic ratios in clinical magnetic resonance spectroscopy.

Characterization of oligodendrogliomas using short echo time 1H MR spectroscopic imaging

“…In vivo MRS at 1.5 T usually lacks sensitivity to distinguish myo-inositol from glycine, both resonating at $3.55 ppm, 33 although the use of different echo times may enable distinction between these metabolites. 34 Different levels of both myo-inositol and glycine have been observed in glial tumors in vivo and in vitro. 22,23,34,35 Interpretation of this data, however, is complicated because of the lower spectral resolution of MRS in vivo than in vitro.…”

“…34 Different levels of both myo-inositol and glycine have been observed in glial tumors in vivo and in vitro. 22,23,34,35 Interpretation of this data, however, is complicated because of the lower spectral resolution of MRS in vivo than in vitro. However, one has to also consider that biopsies and tumor extracts are not necessarily representative for a whole tumor as measured by in vivo MRS, and the tumor volume measured in vivo may contain normal brain tissue as well.…”

Non-invasive grading of astrocytic tumours from the relative contents of myo-inositol and glycine measured by in vivo mrs

“…The method described in (31,36) was also based on the well known fact that the Jmodulation dependent effect on mI resonances would strongly decrease the apparent mI peak intensity at ca. 3.55 ppm at short TE (15,19,20 (6). In typical in vivo spectra ( Fig.…”

“…In addition to those resonances, MRS produces much more information of potential interest for astrocytic tumour grading, e.g. the myo-inositol resonance (ca 3.55 ppm) which can be measured at short echo times (15)(16)(17)(18).…”

Development of a decision support system for diagnosis and grading of brain tumours using in vivo magnetic resonance single voxel spectra

“…Elevated lipids at 0.8 and 1.29 ppm are clear markers of necrosis and will be high in necrotic glioblastomas and metastases. On the other hand, the glycine/myo-inositol signal (compared with creatine) is high in certain highgrade glial tumours (45)(46)(47).…”