  Purpose: To evaluate the feasibility of a 3-minute b-tensor encoding protocol
for diffusion MRI-based assessment of the microscopic anisotropy and tissue
heterogeneity in a wide range of intracranial tumors. Methods: B-tensor
encoding was performed in 42 patients with intracranial tumors (gliomas,
meningiomas, adenomas, metastases). Microscopic anisotropy and tissue
heterogeneity were evaluated by estimating the anisotropic kurtosis ($MK_A$)
and isotropic kurtosis ($MK_I$), respectively. An extensive imaging protocol
was compared with a faster 3-minute protocol. Results: The fast imaging
protocol yielded parameters with characteristics in terms of bias and precision
similar to the full protocol. Glioblastomas had lower microscopic anisotropy
than meningiomas $(MK_A = 0.29 \pm 0.06$ versus $0.45\pm0.08, p = 0.003)$.
Metastases had higher tissue heterogeneity $(MK_I = 0.57\pm0.07)$ than both the
glioblastomas $(0.44\pm0.06, p < 0.001)$ and meningiomas $(0.46\pm0.06, p =
0.03)$. Conclusion: Evaluation of the microscopic anisotropy and tissue
heterogeneity in intracranial tumor patients is feasible in clinically relevant
times frames.
