Role of magnetic resonance spectroscopy & diffusion weighted imaging in differentiation of supratentorial brain tumors

Abstract

Purpose: To evaluate the role of magnetic resonance spectroscopy & diffusion weighted imaging (DWI) in differentiating between primary and secondary brain tumors. Patients & methods: This prospective study was performed for 40 patients. Diffusion weighted image (DWI) and apparent diffusion co-efficient (ADC) maps were acquired by using b-values of 0 and 1000 mm2/s. Standard mean ADC values were calculated automatically and expressed in 10−3 mm2/s in both intra-lesional and peri-lesional regions. Multi voxel MR spectroscopy was performed using a spin-echo mode sequence. The metabolites were identified including the following: N-acetylaspartate (NAA) at 2.0 ppm, creatine (Cr) at 3.0 ppm, choline (Cho) at 3.2 ppm, lipid at the range of 0.7–1.3 ppm, lactate at 1.33 ppm and myoinositol at 3.56 ppm. The ratios that were calculated include the following: Cho/NAA and Cho/Cr in both intralesional and perilesional regions. Results: Intralesional ADC values showed no difference between the metastases (0.6: 1 × 10−3 mm2/s with mean 0.86) and high grade primary tumors (0.6: 1.1 × 10−3 mm2/s with mean 0.73). Perilesional ADC value Findings in the study revealed that primary tumors have low ADC values (0.9: 1.1 × 10−3 mm2/s with mean 0.95) in their peri-lesional voxels denoting peri-lesional infiltration, while higher ADC values in metastasis (1.3–1.6 × 10−3 mm2/s mean 1.41) due to the absence of peri-lesional infiltration increase in CHO/Cr ratios (>1) in primary high grade tumors (indicating perilesional infiltration) while there was no increase in CHO/Cr ratio in cases of metastases. Low grade primary tumors showed low lactate and lipid, with increasing malignancy, and tumors showed increasing levels of lactate and lipid peaks (indicating necrosis) with remarkable difference in lipid peaks between low and high grade tumors. There was no significant difference between primary & metastatic brain tumors as regards lactate peak. Conclusion: Intra-lesional ADC values are not useful in the differentiation between primary and metastatic tumors. Perilesional ADC values can differentiate between primary & metastatic brain tumors. Intralesional MRS values (CHO/Cr ratio) were able to grade the tumor and differentiate between high and low grade tumors, while Perilesional MRS values (CHO/Cr ratio) could be able to differentiate primary tumors from metastasis.

Keywords

• Magnetic resonance imaging
• Brain tumor
• MRS
• DWI