Time-Dependent Diffusion Using Oscillating-Gradient Spin-echo Sequence in Extra-Axial Brain Tumors [Presidential Award Proceedings]

Abstract

　Oscillating-gradient spin-echo (OGSE) prototype sequences can shorten the effective diffusion time (Δ_eff) and add information regarding the internal structure of lesions. The purpose of our study was to investigate the utility of changes in diffusivity between short and long Δ_eff values in distinguishing different types of extra-axial brain tumors. Twelve patients with meningiomas, 13 with acoustic neuromas, and 11 with pituitary adenomas were scanned using a 3T magnetic resonance (MR) scanner. Diffusion tensor imaging (DTI) was performed using b-values of 0 and 1000 s/mm². OGSE imaging using a trapezoid-cosine waveform was performed with Δ_eff values of 6.5 and 35.2 ms. The diffusivity of each tumor was measured after setting a manually defined region of interest (ROI). The relative percentage change between the shorter and longer Δ_eff values was then calculated. The relative percentage changes of the three tumor types were compared using the Steel-Dwass test. The relative percentage changes of λ2, λ3, and mean diffusivity (MD) were significantly higher in pituitary adenomas than in meningiomas and acoustic neuromas, but not significantly different between meningiomas and acoustic neuromas. The dependence of λ2, λ3, and MD on Δ_eff values between 6.5 and 35.2 ms was stronger in pituitary adenomas than in meningiomas and acoustic neuromas, suggesting differences in internal tissue structure. Our results showed that the use of DTI with a shorter Δ_eff provides additional information about the microstructure of brain tumors. OGSE imaging may help in the differentiation of different types of tumors that show atypical imaging findings on conventional MRI.