Abstract

1H MRS thermometry has been investigated for brain trauma and hypothermia monitoring applications but has not been explored in brain tumours. The proton resonance frequency (PRF) of water is dependent on temperature but is also influenced by microenvironment factors, such as fast proton exchange with macromolecules, ionic concentration and magnetic susceptibility. 1H MRS has been utilized for brain tumour diagnostic and prognostic purposes in children; however, the water PRF measure may provide complementary information to further improve characterization. Water PRF values were investigated from a repository of MRS data acquired from childhood brain tumours and children with apparently normal brains. The cohort consisted of histologically proven glioma (22), medulloblastoma (19) and control groups (28, MRS in both the basal ganglia and parietal white matter regions). All data were acquired at 1.5 T using a short TE (30 ms) single voxel spectroscopy (PRESS) protocol. Water PRF values were calculated using methyl creatine and total choline. Spectral peak amplitude weighted averaging was used to improve the accuracy of the measurements. Mean PRF values were significantly larger for medulloblastoma compared with glioma, with a difference in the means of 0.0147 ppm (p < 0.05), while the mean PRF for glioma was significantly lower than for the healthy cohort, with a difference in the means of 0.0061 ppm (p < 0.05). This would suggest the apparent temperature of the glioma group was ∼1.5 °C higher than the medulloblastomas and ∼0.7 °C higher than a healthy brain. However, the PRF shift may not reflect a change in temperature, given that alterations in protein content, microstructure and ionic concentration contribute to PRF shifts. Measurement of these effects could also be used as a supplementary biomarker, and further investigation is required. This study has shown that the water PRF value has the potential to be used for characterizing childhood brain tumours, which has not been reported previously. © 2014 The Authors. NMR in Biomedicine published by John Wiley & Sons, Ltd.

Highlights

  • Cancer is the most common cause of death in children after infancy, and, whilst significant advances have been made, the rate of improvement in survival is decreasing

  • Cho and Cr were used as metabolite references to give the most accurate proton resonance frequency (PRF) shift for groups chosen

  • The spectral peak amplitude-squared weighting of the water PRF was substantially weighted towards the Cho peak value, except in the white matter (WM) group

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Summary

Introduction

Cancer is the most common cause of death in children after infancy, and, whilst significant advances have been made, the rate of improvement in survival is decreasing. One technique is 1H MRS, which is a powerful non-invasive tool for the assessment of childhood brain tumours through MRS pattern classification [1]. A complementary analysis technique, which may provide additional information, is 1H MRS thermometry. 1H MRS thermometry is a non-invasive method to measure brain temperature changes and provide information about the tissue microenvironment. Temperature has been shown to be an important factor in characterizing tumours, with changes in temperature compared with surrounding tissue being observed for different tumour types [2]. Temperature rises have been attributed to abnormalities in vasculature leading to hypoxia and abnormal energy metabolism [4,5], whilst decreases may be associated with the presence of necrosis. Hypoxia has been shown to increase treatment resistance in brain tumours,

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