Towards the Assessment of Intracellular Viscosity: Diffusion Spectroscopy at Ultra-Short Diffusion Time in the Rat Brain

Charlotte Marchadour¹, Martine Guillermier¹, Diane Houitte¹, Marion Chaigneau¹, Philippe Hantraye¹, Vincent Lebon¹, Julien Valette¹

Given the intracellular compartmentation of brain metabolites, diffusion-weighted (DW) spectroscopy is a unique tool to assess properties of the intracellular space. Long diffusion times T_d are traditionally used for DW-spectroscopy, yielding apparent diffusion coefficient (ADC) that depend on restriction. In contrast, ADC measured for shorter T_d would reflect free diffusion and yield an indirect estimate of intracellular viscosity. Using a modified LASER sequence incorporating oscillating gradients, we could measure ADC of NAA, creatine and choline for T_d down to ~1 ms. It is shown that metabolite ADC dramatically increases as T_d decreases, approaching values consistent with the free diffusion regime.