Polynomial fitting of DT-MRI fiber tracts allows accurate estimation of muscle architectural parameters

Fiber curvature is a functionally significant muscle structural property, but its estimation from diffusion-tensor magnetic resonance imaging fiber tracking data may be confounded by noise. The purpose of this study was to investigate the use of polynomial fitting of fiber tracts for improving the accuracy and precision of fiber curvature (kappa) measurements. Simulated image data sets were created in order to provide data with known values for kappa and pennation angle (theta). Simulations were designed to test the effects of increasing inherent fiber curvature (3.8, 7.9, 11.8 and 15.3 m(-1)), signal-to-noise ratio (50, 75, 100 and 150) and voxel geometry (13.8- and 27.0-mm(3) voxel volume with isotropic resolution; 13.5-mm(3) volume with an aspect ratio of 4.0) on kappa and theta measurements. In the originally reconstructed tracts, theta was estimated accurately under most curvature and all imaging conditions studied; however; the estimates of kappa were imprecise and inaccurate. Fitting the tracts to second-order polynomial functions provided accurate and precise estimates of kappa for all conditions except very high curvature (kappa=15.3 m(-1)), while preserving the accuracy of the theta estimates. Similarly, polynomial fitting of in vivo fiber tracking data reduced the kappa values of fitted tracts from those of unfitted tracts and did not change the theta values. Polynomial fitting of fiber tracts allows accurate estimation of physiologically reasonable values of kappa, while preserving the accuracy of theta estimation. (C) 2012 Elsevier Inc. All rights reserved.