Quantification Of Glx In Intracranial Tumors Using Magnetic Resonance Spectroscopy

Purpose: To investigate the value of Glx quantification in diagnosing and grading intracranial tumors using 1H-MRS. To explore whether change of Glx/Cr peak ratios reflect change of Glx concentrations in intracranial tumors.Methods: Forty-one patients with intracranial tumors and nine healthy volunteers were examined by in vivo 1H-MRS. Single-voxel spectra were acquired using the point-resolved spectroscopic pulse sequence with GE 1.5-T MRI system(TR/TE/Ave=3000ms/30ms/64). Voxel sizes ranged from (12mm) 3 to (20mm)3. Glx and Cr concentrations were quantificated by LCModel automatically. Glx/Cr concentration ratios were calculated. After measuring the peak height of Glx and Cr, Glx/Cr peak ratios were calculated. Diagnoses of the patients were confirmed pathologically and clinically.Results:1.Glx concentrations, Glx/Cr concentration ratios and Glx/Cr peak ratios were significant different among normal brain tissue, meningeomas, astrocytomas and metastases(P<0.01). They presented higher in meningeomas compared with normal brain tissue, astrocytomas and metastases(P<0.05).2.Compared with normal brain, Glx concentrations were significantly elevated in meningeomas(P<0.05),but showed no significant change in astrocytomas(P>0.05) and metastases(P>0.05). Glx/Cr concentration ratios elevated in meningeiomas (P<0.01), astrocytomas(P<0.01) and metastases(P<0.01). Glx/Cr peak ratios also elevated in meningeomas(P<0.01), astrocytomas(P<0.05) and metastases(P<0.01).3.Compared with high-grade astrocytomas, Glx concentrations were higher in low-grade astrocytomas(P<0.05), while Glx/Cr concentration ratios and peak ratios were lower in low-grade astrocytomas(P<0.05).4.Three indexs of Glx showed no significant difference between astrocytomas and metastases(P>0.05)and showed no significant difference between metastases and high-grade astrocytomas(P>0.05).5.The correlation between Glx concentrations and Glx/Cr concentration ratios was weak with r=0.338(P=0.047). A positive correlation was found between Glx/Cr concentration ratios and Glx/Cr peak ratios with r=0.932(P=0.000). No correlations were observed between Glx concentrations and Glx/Cr peak ratios with r=0.254(P=0.141).Conclusion: Quantification of Glx using 1H-MRS shows a promising role in differentiating meningiomas from other intracranial tumors. Glx concentrations,Glx/Cr concentration ratios and peak ratios show higher in meningiomas than normal brain tissue, astrocytomas and metastases. Quantification of Glx may be useful for grading astrocytomas, but needs further study. The value of Glx quantification in tumor masses can not help in discriminating primary brain tumors from metastases. However, the value of Glx quantification in peritumoral edema is expected to explore. Change of Glx/Cr peak ratios fails to reflect change of Glx absolute concentrations in intracranial tumors.