Abstract #2637
            The effect of diffusion in the extracellular space on double-PFG measurements of axon size: Insights from Monte-Carlo simulations
                      Gregory T Baxter                     1                    , Vitaly Galinsky                     1                    , 						Evren Ozarslan                     2                    , Peter J Basser                     3                    , 						and Lawrence R Frank                     1,4          
            
            1
           
           Center for Scientific Computation in 
						Imaging, Dept. of Radiology, University of California, 
						San Diego, CA, United States,
           
            2
           
           Department 
						of Radiology, Brigham and Women's Hospital, Harvard 
						Medical School, Boston, MA, United States,
           
            3
           
           Section 
						on Tissue Biophysics and Biomimetics, PPITS, NICHD, 
						National Institutes of Health, Bethesda, MD, United 
						States,
           
            4
           
           Center 
						for Functional MRI, Dept of Radiology, University of 
						California, San Diego, CA, United States
          
            
          We present Monte-Carlo simulations of diffusion within 
						hexagonally packed arrays of cylinders mimicking the 
						white-matter, and report the signal behavior for 
						double-PFG experiments with zero mixing times. We 
						investigate the accuracy of the axonal diameter 
						estimates when a bi-compartmental model that assumes 
						Gaussian diffusion outside the cells is employed. 
						Despite the substantially underestimated bulk 
						diffusivity values, cell diameter and volume fraction 
						estimates are both adequately captured by such a 
						bi-compartmental model. Some underestimation of cell 
						diameters is expected only for tightly packed 
						configurations.
         
				
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