Imaging cell size and permeability in biological tissue using the diffusion-time dependence of the apparent diffusion coefficient.
The purpose of this study was to analyze and evaluate a model of restricted water diffusion between equidistant permeable membranes for cell-size and permeability measurements in biological tissue. Based on the known probability distribution of diffusion distances after the diffusion time τ in a system of permeable membranes characterized by three parameters (membrane permeability P, membrane distance L, and free diffusivity D0), an equivalent dimensionless model was derived with a probability distribution characterized by only a single (dimensionless) tissue parameter [Formula: see text]. Evaluating this proposed model function, the dimensionless diffusion coefficient [Formula: see text] was numerically calculated for 60 values of the dimensionless diffusion time [Formula: see text] and 35 values of [Formula: see text]. Diffusion coefficients were measured in a carrot by diffusion-weighted magnetic resonance imaging (MRI) at 18 diffusion times between 9.9 and 1022.7 ms and fitted to the simulation results [Formula: see text] to determine L, P, and D0. The measured diffusivities followed the simulated dependence of [Formula: see text]. Determined cell sizes varied from 21 to 76 μm, permeabilities from 0.007 to 0.039 μm(-1), and the free diffusivities from 1354 to 1713 μm(2) s(-1). In conclusion, the proposed dimensionless tissue model can be used to determine tissue parameters (D0, L, P) based on diffusion MRI with multiple diffusion times. Measurements in a carrot showed a good agreement of the cell diameter, L, determined by diffusion MRI and by light microscopy.
Josef Lissner Laboratory for Biomedical Imaging, Institute for Clinical Radiology, Ludwig-Maximilians-University Hospital Munich, Marchioninistr 15, D-81377 Munich, Germany. Department of Neuroradiology, Heidelberg University Hospital, Im Neuenheimer Feld 400, D-69120 Heidelberg, Germany.
Olaf
O
Dietrich
Alexander
A
Hubert
Sabine
S
Heiland
D002463:Cell Membrane Permeability; D048429:Cell Size; D018552:Daucus carota / Q000166:cytology; D004058:Diffusion; D038524:Diffusion Magnetic Resonance Imaging; D013997:Time Factors