Diagnostic potential of short echo time MR spectroscopy of gliomas with single-voxel and point-resolved spatially localised proton spectroscopy of brain

Abstract

Accurate neuroimaging grading of gliomas is useful for management, but techniques such as MRI and CT are not sufficiently reliable. Necrosis is a consistent, decisive prognostic factor and the key diagnostic criterion for glioblastoma multiforme. MR spectroscopy (MRS) allows noninvasive measurement of metabolites in brain tumours and mobile lipids reflect necrosis. However, short echo-time (TE) spectroscopy has been required for reliable assessment of lipids, since their relaxation times are very short. Recent advances have made it possible to perform short-TE MRS. We attempted to evaluate the significance of short TE spectroscopy as part of routine imaging for diagnosis and grading of gliomas. We performed TE 30 ms MRS in 25 patients with gliomas (grade II six; grade III three; grade IV, 16) and in 19 areas of healthy white matter using proton brain examination/single voxel (PROBE/SV) and point-resolved spatially localised spectroscopy (PRESS). With short-TE spectroscopy, lipid signals were detected in all 16 tumours of grade IV, one grade II (P = 0.0002) and none of grade III (P = 0.001). TE 136 ms MRS, carried out in 20 of these cases, showed lipid signals in only four of 14 grade IV tumours and in none of the other six. N-acetylaspartate/choline (NAA/Cho) ratios were always more than 1.0 in healthy tissues and less than 1.0 in all but one of the gliomas. The mean creatine (Cr)/Cho ratio in each tumour grade was significantly lower than in the healthy tissues. The mean Cr/Cho ratio was also significantly lower in grade IV than in grade II tumours (P < .0005). Considerable overlap in Cr/Cho ratio was observed between grade II and grades III and IV gliomas at long but less so at short-TE MRS. We conclude that short-TE MRS with PROBE/SV and PRESS is of value in grading gliomas.

Iterative averaging of spectra as a powerful way of suppressing spurious resonances in signal processing

“…Consequently, reliance upon metabolite concentration ratios becomes particularly precarious. For example, in addition to NAA at ∼2.05 ppm, metabolites Glu and Gln within 2.1-2.5 ppm may contribute to the spectral area around 2.0 ppm at short TEs [25]. It thus becomes more difficult to assess NAA levels at short TEs due to heavily overlapping resonances that cannot be reliably identified using the FFT followed by fitting.…”

Imaging hypoxia in gliomas

“…Furthermore, functional DCE-MRI images have been integrated in radiotherapy treatment planning in combination with morphological CT images [194]. H-magnetic resonance spectroscopy 1 H-magnetic resonance spectroscopy can provide useful metabolic information for brain tumour diagnosis and glioma grading [195,196]. Two metabolites, lipids and lactates, both of which are present on short-and long-echo time (TE) sequences, have been studied as hypoxia markers.…”

“…The relationship between lipids and glioma grade is well established [196,200]. The significance of lactates, which are the end product of anaerobic metabolism, in grading is more controversial [195,[200][201][202][203]. Either lipid or lactate signals have been identified in hypoxic areas and have been correlated with the rCBV in malignant gliomas [204].…”

Molecularly Targeted Therapies for Malignant Gliomas

“…Apart from the standard MRI imaging techniques, novel molecular imaging techniques-such as arterial spin labeling, perfusion MRI (62), 1 H-magnetic resonance spectroscopy (63), and blood oxygenation level-dependent imaging (64)-have recently been shown to provide quantitative measurements of brain tumor perfusion. Single-photon emission computed tomography and positron emission tomography imaging have been recently applied in the clinical setting and may be sensitive quantitative techniques to objectively assess the efficacy of antiangiogenic therapy in MGs, providing some useful information (65).…”