No description available.

No description available.

No description available.

We investigate the diffusion of particles on heterogeneous lattices with two kinds of nonequivalent sites. General analytical expressions for the chemical and jump diffusion coefficients have been derived in the case of strong inhomogeneity. We have calculated coverage dependencies of the diffusion coefficients and other necessary thermodynamic quantities for some representative values of the lateral pairwise interaction between the particles. The analytical data have been compared with the numerical data obtained by the kinetic Monte Carlo simulations. Almost perfect agreement between the respective results has been found.

Restricted diffusion of gas in the lung is in many ways similar to restricted diffusion in other porous media: atomic collisions with boundaries restrict the measured value, and there is a critical dependence on the time and distance scales of the measurement. The large free diffusivity of gases allows large pores (300 microns or larger) to be studied. The high signals of hyperpolarization permit rapid diffusion imaging of the gas itself, though fluorinated hydrocarbons are simple by comparison and are a potential alternative. The complicated nature of bifurcating human lung structure provides challenges in interpretation of results of restricted diffusion. At times sufficiently short, the short-time slope of D(t)/D0 can be related to the surface-to-volume ratio - an important measure of lung structure and early emphysema. During times of a few milliseconds, diffusion anisotropy is observed, and the principal components of diffusion are related to geometric parameters of individual airways within the pulmonary acinus. This permits regional invivo lung morphometry, which gives spatial information about features and airway geometry much smaller than the imaging voxel size. The extraordinarily long T1 of 3He provides the opportunity to use stimulated echoes to probe long diffusion times and distances. Preliminary evidence indicates that for distances significantly larger than a pulmonary acinus (≥ 1 cm), the measured diffusivity is severely restricted (near 0.02 cm2/s) and is dominated by diffusion through collateral routes. This implies that the longrange ADC measurement of 3He in lungs is an exquisitely sensitive measure of collateral airway paths.

No description available.

The rapid-acquisition of q-space data from 1H2O undergoing restricted diffusion in suspensions of red blood cells (RBCs) is made possible using a recently implemented pulse sequence, where the phase cycling of the radio-frequency pulses is reduced by using unbalanced pairs of bipolar magnetic field-gradient pulses. The q-space plots obtained with this pulse sequence show a shift in the position of the first diffraction minimum when compared to data from classical pulsed field gradient stimulated echo experiments. Diffusion simulations were used to investigate the effect of the additional delay introduced by the bipolar gradient pulses on the form of the q-space plots. RBCs of normal discocyte shape align with an external magnetic field, and the angular dependence of q-space spectra from suspensions of RBCs was examined using a linear combination of gradients applied along the y- and z-axes. The resulting q-space plots showed a gradual disappearance of the first diffraction minimum as the angle at which the gradients were applied was changed from 0° (along the z-axis) to~40°, beyond which the q-space plots showed no diffraction features. These experimental results were also evident in Monte-Carlo random walk simulations of diffusion in RBCs with field-gradients applied at varying angles with respect to cells aligned with B0.

No description available.

No description available.

No description available.