Image Processing of Diffusion Tensor MRI Data - Advance Image Processing in Magnetic Resonance Imaging - page 418

13

Image Processing
of Diffusion Tensor
MRI Data

Lauren O'Donnell, Steven Haker,
and Carl-Fredrik Westin

CONTENTS

13.1 Introduction............................................................................................427
13.2 Diffusion and Diffusion Tensor Calculation .........................................429
13.3 Anisotropy and Macrostructural Measures ...........................................430
13.3.1 Geometrical Measures of Diffusion........................................431
13.3.2 Macrostructural Tensor and Diffusive Measures....................434
13.4 Visualization of Diffusion Tensors ........................................................438
13.5 Connectivity Analysis ............................................................................440
13.6 Method One: Diffusion-Based Connectivity.........................................441
13.6.1 Experiments.............................................................................442
13.7 Method Two: Distance-Based Connectivity..........................................443
13.7.1 Measuring Distances in the Tensor-Warped Space ................445
13.7.2 Experiments.............................................................................445
13.8 Conclusion .............................................................................................446
Acknowledgments .............................................................................................448
References .........................................................................................................448

13.1 INTRODUCTION

Diffusion magnetic resonance imaging (MRI) measures the random molecular
motion (diffusion) of water in biological tissue. Tissues with an oriented structure,
such as the fibers of muscle or the axons of nervous tissue, produce measurable
diffusion anisotropy: a pattern is imposed on the diffusing molecules by the shape

of the tissue. One such tissue is shown in Figure 13.1 , an image of some major

white matter fiber tracts in a sagittal view of the human brain. Fiber tracts are
bundles of neurons whose membranes hinder water diffusion [5]. The orientation
of cells in neural tissue is thus reflected in MRI measurements of water diffusion,

which vary with direction. This is shown schematically in Figure 13.2 .

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