PRELIMINARY REPORT In Vivo Visualization of White Matter Fiber Tracts of Preterm- and Term-Infant Brains With Diffusion Tensor Magnetic Resonance Imaging Seung-Schik Yoo, PhD,*‡ Hae-Jeong Park, PhD,* Janet S. Soul, MD,† Hatsuho Mamata, MD, PhD,* HyunWook Park, PhD,§ Carl-Fredrik Westin, PhD,* Haim Bassan, MD,† Adre J. Du Plessis, MD,† Richard L. Robertson Jr., MD,¶ Stephan E. Maier, MD, PhD,* Steven A. Ringer, MD, PhD, Joseph J. Volpe, MD,† and Gary P. Zientara, PhD* Objective: The goal of this study was to test the feasibility of visualizing a 3-dimensional structure of cerebral white matter fiber tracts in preterm infants, postconceptional age (PCA) 28 weeks to term, by using volumetric diffusion tensor magnetic resonance imaging (DTI) data. Materials and Method: We combined tractography algorithms and visualization methods, currently available for adult DTI data, to trace the pixelated principal direction of a diffusion tensor originat- ing from regions-of-interest with high fractional anisotropy. Conse- quently, white matter fiber bundles from the genu and the splenium of corpus callosum, the corticospinal tracts, the inferior fronto- occipital fasciculi, and optic radiations were visualized. Results: Our results suggest that major white matter tracts of preterm infant brains, with PCAs ranging from 28 weeks to term (40 weeks old), can be successfully visualized despite the small brain volume and low anisotropy. Conclusion: The feasibility of fiber tractography in preterm neo- nates with DTI may add a new dimension in detection and charac- terization of white matter injuries of preterm infants. Key Words: white matter, neonates, diffusion, imaging, neurodevelopment (Invest Radiol 2005;40: 110 –115) D iffusion tensor magnetic resonance imaging (DTI) char- acterizes the diffusion of water molecules by using motion-probing spatial encoding. 1–4 A voxel-specific diffu- sion tensor acquired through DTI represents 3 orthogonal principal axes of diffusion, with the eigenvalue equal to the apparent diffusion coefficient (ADC) along each axis. During human neurodevelopment, a degree of anisotropy may exist in a neonatal brain before the histologic appearance of my- elination. 5,6 The early myelination process hinders isotropic free diffusion, and consequently creates diffusion anisotropy along white matter (WM) axonal tracts. 7–9 Therefore, DTI (and diffusion-weighted imaging) has been used to examine the degree of myelination during early neurodevelop- ment 10 –13 as well as to detect differences in maturation of WM among premature infants. 14 –18 WM tractography (or “WM fiber tracking”) techniques have been developed to establish interregional connectivity between major WM tracts by tracing the path of greatest diffusivity. 19 –24 Estimating the orientation of the diffusion tensor, especially from preterm/term infant brain data, is challenging because the magnitude of the magnetic resonance signal is generally reduced in neonates as a result of the smaller voxel size needed for resolving their smaller ana- tomic structures. In addition, the developing infant brain possesses vastly different tissue characteristics from the adult brain in numerous aspects such as its water content and degree of myelination, 25,26 thereby reducing the anisotropy values in the WM tracts. 17,27,28 These factors potentially confound the ability to track WM fibers accurately. Received July 17, 2004 and accepted for publication, after revision, October 3, 2004. From the Departments of *Radiology and Newborn Medicine, Brigham and Women’s Hospital and Harvard Medical School, Boston, Massachusetts; the Departments of †Neurology and ¶Radiology, Children’s Hospital Boston, Harvard Medical School, Boston, Massachusetts; and the De- partments of ‡BioSystems and §Electrical Engineering, Korea Advanced Institute of Science and Technology, Korea. This study was partially supported by the William Randolph Hearst Fund, the Brain Neuroinformatics Research Program, Korean Ministry of Science and Technology Grant #2004-55-02038 (to S-SY), NIH R03-HD041376 (to GPZ), P01-NS38475-5 (to AJdP, GPZ), NIH R01-NS39335 (to SEM) and the United Cerebral Palsy Foundation (to JS). Reprints: Seung-Schik Yoo, PhD, Department of Radiology, Brigham and Women’s Hospital, Harvard Medical School, 75 Francis Street, Boston, MA. E-mail: yoo@bwh.harvard.edu. Copyright © 2005 by Lippincott Williams & Wilkins ISSN: 0020-9996/05/4002-0110 Investigative Radiology • Volume 40, Number 2, February 2005 110