Feasibility of diffusion-NMR surface-to-volume measurements tested by calculations and computer simulations.
It has been demonstrated previously that the surface-to-volume ratio S/V can be determined from the derivative of the time-dependent diffusion coefficient D(t), in the limit t --> 0. Several questions arise concerning the practicality of determining S/V by NMR. In particular, how large are the errors generated by (1) working outside the t --> 0 limit and (2) measuring D outside the b --> 0 limit, both for narrow and full-width gradient pulses? Here b is gamma2G2delta2Delta for narrow pulses and gamma2G2t3/12 for broad pulses. These questions are addressed by random-walk computer simulations and numerical calculations in geometries relevant to small-airways of lung. The results demonstrate that one can work well outside the t --> 0 and b --> 0 limits, provided 10-20% accuracy in the measured S/V is sufficient. Emphasis is placed on the useful range of times t for which NMR determinations of lung S/V are feasible.
Conradi
Mark S
MS
Department of Physics, Washington University, St. Louis, MO 63130-4899, USA. msc@wuphys.wustl.edu
Bruns
Matthew A
MA
Sukstanskii
Alexander L
AL
Gross
Samuel S
SS
Leawoods
Jason C
JC
D000465:Algorithms; D003198:Computer Simulation; D004058:Diffusion; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D005240:Feasibility Studies; D006801:Humans; D009682:Magnetic Resonance Spectroscopy; D008954:Models, Biological; D011650:Pulmonary Alveoli / Q000378:metabolism; D011653:Pulmonary Diffusing Capacity / Q000502:physiology; D013997:Time Factors