Foreword by the Guest Editors: Diffusion NMR and MRI: Basic Concepts and Applications

Pulsed gradicnl magnetic resonance (MR) measurement of diffusion, which is the subject of the present issue, exhibited dramatic developments in the paht two dccades. These developments encompass technological, methodological, and theoretical issues, as well as novel applications. This special issue oflhe Ismel J r ~ u r n d qf Chenzi~rry, "'Diffusion NMR and MRI: Basic Concepts and Applicarions", attempts to dernon~trate the interdisciplinary nnuturc id the subject and the range oi' applications to which diffusion MR contributes. Sincc pulsed p d i e n t MR techniques provide means for studying diffusion in complex systems without affecting the system and totally noninvasively, djffusion MR became the method of choice for measuring difision and flow in chemical and biological systems in the last twenty years or so. The lechnique is used in solution and polymer chemistry, material science, biology, medical research, and medical diagnosis. Pulsed gradient NMR and MRI are currently used to study supramolecular systems i n solution. porous materials. surfactants, zeolites, and catalysts In characterize flow in complex fluids, to study micrustructure, microdynamtcs. and compxtmentalization in cells and organs, and to p~ovide a mean5 of' noninvasively studying tumors, including brain tumors and severe neurological disorders such as stroke, brain trauma, rnuItiple sclerc~sis (MS), and other white matter associated disorders, as well as aging, dementia, and other neuropsychiatric disorders. Recently, diffusion tensor imaging (DTT) was found to be extremely important in mapping white matter fiber tracts in the central nervous system and in studying microstructure of white matter. The concept of molecular diffusion was proposed more than a century ago and the fact that molecular diffusion can be measured by NMR methods was realized by Hahn and othcrs in the early days of NMR spectroscopy. The most practical pulse sequence to measure diffusion with NMR was introdused by Slejskal and Tanner in the mid-sixties, long before the advent of twodimensional NMR (2D-NMR). However the widespread util ixation of diffusion measurements by NMR had to await i~nprovernent in gradient technology, which accumed during the seventies and the eighties with the developmenl of MRJ and the realization that coherence selection can be achieved efficiently by gradient puIses. Today. p d i e n t coils are standard in conventional highresolution NMR spectrometers, and very strong and eff~cient gradient coils are commercially available, making these techniqueb accessible to a large number of researchers. Indeed, the last decade bmught about a dramatic increase in the utilization of diffusion NMR in so many fields and disciplines, making it nearIy impossible to cover all aspects of diffusion NMR and MRI in a single vofume. This issue presents an attempl to span a wide range of methodolngical aspects covering basic issues of diffusion NMR, applications in cells and organs, and exkending up to diffusion MRT in humans. We believe that these papers, some of which were written by leading scientists in Ihe field of diffusion MR, provide a glimpse of the interdisciplinary nature of the subject and the vast promise that application of these techniques holds. We hope that this volume will ellcourage new scientists to join this exciting scientific endewor. Last but not least. we wish lo thank rhc editorial board of the Juiir~nl for inviting us to edit this issue and a11 the cantributors lo this issue for their contributions and remarkable collaboration.