QUANTITATION OF NON-EINSTEIN DIFFUSION BEHAVIOR OF WATER IN BIOLOGICAL TISSUES BY PROTON MR DIFFUSION IMAGING - SYNTHETIC IMAGE CALCULATIONS

The non-Einstein diffusion behavior of water in a model biological tis sue system, intact duck embryos, has been investigated by the use of a n in vivo proton pulsed-gradient spin-echo (PGSE) MR imaging technique . Multiple-frame MR images of the intact duck embryos and control solu tion (0.5 mM CuSO4 doped water) were acquired systematically at differ ent diffusion times and strengths of the diffusion-sensitizing magneti c field gradients of the PGSE sequence. These raw images were then use d to generate various dynamic (self-diffusion coefficient) and structu ral (fractal, residual attenuation, and compartment fraction) diffusio n parameter maps of water in the imaging objects on the basis of diffe rent Einstein and higher order (non-Brownian, Residual, and 2-compartm ent) diffusion models. The self-diffusion coefficients of the body tis sues of the embryos obtained from all diffusion models were significan tly lower than those of the surrounding embryonic fluid. The structura l diffusion parameter maps obtained from the higher order diffusion mo dels revealed that water molecules exhibited either non-Brownian, rest ricted, or compartmentalized diffusion behavior in the embryonic tissu es, but Einstein or Brownian diffusion behavior in the embryonic fluid and control solution. The diffusion parameter maps, both dynamic and structural, were found to provide much better contrasts than the conve ntional relaxation time (T1, T2, and biexponential T2) maps in separat ing the tissues from the surrounding embryonic fluid in the duck embry os. The mathematical models and procedures for generating the dynamic and structural diffusion parameter maps are also presented in this pap er.