MR spectroscopy in post-treatment follow up of brain tumors

PurposeTo detect the role of MR spectroscopy in evaluating the whole area of signal alteration within the irradiated volume aiming to differentiate recurrent/residual tumors from radiation injury and to detect the tumor margin and extent.Materials and methodsThis prospective study included 25 patients with previously treated primary intracranial tumors. All patients received radiotherapy. MRI and multivoxel MRS were performed. The volume of interest was placed over the whole area of signal alteration. The spectra were analyzed for the signal intensity of choline (Cho), creatine (Cr), and N-acetyl aspartate (NAA), lipid (Lip), lactate (Lac), and myo-inositol (mI). Metabolite ratios for Cho/NAA, Cho/Cr, and NAA/Cr were calculated.ResultsCho/NAA and Cho/Cr were significantly higher while NAA/Cr ratios were significantly lower in tumors than radiation injury (p = 0.001 for all ratios). The Cho/NAA and Cho/Cr ratios were significantly higher in radiation injury than in normal-appearing brain tissue (p = 0.032 and p = 0.008, respectively), whereas NAA/Cr was insignificantly lower in radiation injury than normal-appearing brain tissue (p = 0.051). Value >1.8 for Cho/NAA ratio was considered as indicator for tumor.ConclusionMR spectroscopy can differentiate recurrent/residual tumor from radiation injury and delineate the tumor margin and extent.