Intracellular water specific MR of microbead-adherent cells: HeLa cell intracellular water diffusion

The ¹H MR signal arising from flowing extracellular media in a perfused, microbead-adherent cultured cell system can be suppressed with a slice-selective, spin-echo pulse sequence. The signal from intracellular water can, thus, be selectively monitored. Herein, this technique was combined with pulsed field gradients (PFGs) to quantify intracellular water diffusion in HeLa cells. The intracellular water MR diffusion-signal attenuation at various diffusion times was well described by a biophysical model that characterizes the incoherent displacement of intracellular water as a truncated Gaussian distribution of apparent diffusion coefficients (ADCs). At short diffusion times, the water "free" diffusion coefficient and the surface-to-volume ratio of HeLa cells were estimated and were, 2.0 ± 0.3 μm²/ms and 0.48 ± 0.1 μm^-1 (mean ± SD), respectively. At long diffusion times, the cell radius of 10.1 ± 0.4 μm was inferred and was consistent with that measured by optical microscopy. In summary: 1) intracellular water "free" diffusion in HeLa cells was rapid, two-thirds that of pure water, and 2) the cell radius inferred from modeling the incoherent displacement of intracellular water by a truncated Gaussian distribution of ADCs was confirmed by independent optical microscopy measures.