Comparison of T₁ and T₂ metabolite relaxation times in glioma and normal brain at 3T

Abstract

Purpose: To measure T 1 and T 2 relaxation times of metabolites in glioma patients at 3T and to investigate how these values influence the observed metabolite levels. Materials and Methods:A total of 23 patients with gliomas and 10 volunteers were studied with single-voxel two-dimensional (2D) J-resolved point-resolved spectral selection (PRESS) using a 3T MR scanner. Voxels were chosen in normal appearing white matter (WM) and in regions of tumor. The T 1 and T 2 of choline containing compounds (Cho), creatine (Cr), and N-acetyl aspartate (NAA) were estimated.Results: Metabolite T 1 relaxation values in gliomas were not significantly different from values in normal WM. The T 2 of Cho and Cr were statistically significantly longer for grade 4 gliomas than for normal WM but the T 2 of NAA was similar. These differences were large enough to impact the corrections of metabolite levels for relaxation times with tumor grade in terms of metabolite ratios (P Ͻ 0.001). Conclusion:The differential increase in T 2 for Cho and Cr relative to NAA means that the ratios of Cho/NAA and Cr/ NAA are higher in tumor at longer echo times (TEs) relative to values in normal appearing brain. Having this information may be useful in defining the acquisition parameters for optimizing contrast between tumor and normal tissue in MR spectroscopic imaging (MRSI) data, in which limited time is available and only one TE can be used. GLIOMAS ACCOUNT FOR THE MAJORITY of primary brain tumors and vary from benign to malignant. Among all the gliomas, glioblastoma multiforme (GBM) is both the most common and the most malignant, with a relatively poor prognosis. Proton magnetic resonance spectroscopy ( 1 H-MRS) is a powerful noninvasive tool that has been used for the assessment of metabolites in gliomas and the biochemical profiles of brain tumors have been widely studied (1-4). A general marker of brain tumors is the elevation of choline-containing compounds (Cho), which is thought to be due to increased cell density and membrane turnover in neoplasms, and the reduction of the neural marker Nacetyl aspartate (NAA). The availability of higher field strength MR scanners and multichannel radio frequency coils offer the potential of higher signal-to-noise ratio (SNR) and better spectral resolution (5) that can be used to either shorten acquisition time, decrease spatial resolution, or improve detection of other brain metabolites; such as, glutamate (Glu), a main excitatory neurotransmitter; glutamine (Gln), which acts as a detoxifier; and myo-inositol (mI), which is predominantly located within astrocytes.In planning the data acquisition parameters for using MR spectroscopic imaging (MRSI) to determine the spatial extent of tumor vs. normal brain tissue, it is important to consider how to select values that will emphasize the contrast between metabolites in the different regions. Because of the restrictions on clinical scan time, the repetition time (TR) for acquiring MRSI data is often set at one to two seconds and it is usually only possible to acq...

T1 and T2 Metabolite Relaxation Times in Normal Brain at 3T and 7T

“…Due to lengthening T1 relaxation times and shortening T 2 relaxation times, metabolite resonances were more saturated at 7T compared to those at 3T. Previous research describing the opposing changes in T 2 for Cho and tCr relative to NAA suggests that ratios of Cho/NAA are higher in brain tumor than normal appearing brain at longer echo times [27]. This suggests that longer TR and shorter TE are beneficial for spectral acquisitions at 7T to utilize the SNR gained with increasing field strength and that a lower TE at 7T should be considered for clinical applications.…”

“…Compared with each individual echo spectra, the TEaveraged spectrum has a flat baseline, but preserved metabolites such as Glu, by cancelling the sidebands of multiplets thus providing more accurate quantification. Although TE-averaged PRESS has been widely used in clinical studies [5][6][7][8], its benefits have not been evaluated at ultra-high field strengths.…”

Imaging Tumor Metabolism Using In Vivo Magnetic Resonance Spectroscopy

“…A switch from GPC to PC was found to associate with glioma malignancy [9]. Cr and PCr are involved in ATP metabolism, and altered levels of total Cr have been reported in glioma [10]. Lac, which is a marker of anaerobic metabolism, overlaps with Lip signals that arise from necrosis or from contamination due to subcutaneous Lip.…”

“…At short echo time, the contrast between tumor and normal tissues in MRS data are different from the long echo time spectra because of differential increase in T2 relaxation time for Cho and Cr relative to NAA [10]. Not only do the metabolites with low concentration and/or complex coupling patterns appear in short echo time MRS, but the magnitudes of water and lipid are also increased.…”

Reproducibility of total choline/water ratios in mouse U87MG xenograft tumors by 1H‐MRS

“…In this regard, Sijens and Oudkerk (28) demonstrated, using TR values varying from 1500-5000 msec, that choline and other metabolite profiles were not affected by differential T1 saturation in human brain tumors. In addition, metabolite T1 relaxation values in gliomas have been found not to be significantly different from values in normal white matter (28,29). Thus, the TR value of 1.5 seconds used in the current study is unlikely to have had a substantial effect on the choline measurements or the robustness of our findings with respect to total choline/water ratios.…”