Revealing tumor microstructure with oscillating diffusion encoding MRI in pre-surgical and post-treatment glioma patients

Purpose: We hypothesized that the time-dependent diffusivity at short diffusion times, as measured by oscillating gradient spin echo (OGSE) diffusion MRI, can characterize tissue microstructures in glioma patients.

Theory and methods: Five adult patients with known diffuse glioma, including two pre-surgical and three with new enhancing lesions after treatment for high-grade glioma, were scanned in an ultra-high-performance gradient 3.0T MRI system. OGSE diffusion MRI at 30-100 Hz and pulsed gradient spin echo diffusion imaging (approximated as 0 Hz) were obtained. The ADC and trace-diffusion-weighted image at each acquired frequency were calculated, that is, ADC (f) and TraceDWI (f).

Results: In pre-surgical patients, biopsy-confirmed solid enhancing tumor in a high-grade glioblastoma showed higher $\frac{\mathrm{ADC}\left(f\right)}{\mathrm{ADC}\left(0\mathrm{Hz}\right)}$ and lower $\frac{\text{TraceDWI}\left(f\right)}{\text{TraceDWI}\left(0\mathrm{Hz}\right)}$ , compared to that at same OGSE frequency in a low-grade astrocytoma. In post-treatment patients, the enhancing lesions of two patients who were diagnosed with tumor progression contained more voxels with high $\frac{\mathrm{ADC}\left(f\right)}{\mathrm{ADC}\left(0\mathrm{Hz}\right)}$ and low $\frac{\text{TraceDWI}\left(f\right)}{\text{TraceDWI}\left(0\mathrm{Hz}\right)}$ , compared to the enhancing lesions of a patient who was diagnosed with treatment effect. Non-enhancing T₂ signal abnormality lesions in both the pre-surgical high-grade glioblastoma and post-treatment tumor progressions showed regions with high $\frac{\mathrm{ADC}\left(f\right)}{\mathrm{ADC}\left(0\mathrm{Hz}\right)}$ and low $\frac{\text{TraceDWI}\left(f\right)}{\text{TraceDWI}\left(0\mathrm{Hz}\right)}$ , consistent with infiltrative tumor. The solid tumor of the glioblastoma, the enhancing lesions of post-treatment tumor progressions, and the suspected infiltrative tumors showed high diffusion time-dependency from 30 to 100 Hz, consistent with high intra-tumoral volume fraction (cellular density).

Conclusion: Different characteristics of OGSE-based time-dependent diffusivity can reveal heterogenous tissue microstructures that indicate cellular density in glioma patients.