Key words
TDI : A New Generation Super-Resolution DTI (Diffusion Tensor Imaging) Technique
7.0-T MRI DTI with New TDI (Track-Density Imaging) Technique
Abstract & Summary
One of the most important advances in the field of neuroscience and brain related research is the development of the visualizing technique of the human nervous system or white matter atlas in-vivo. MRI white matter tractography and track densitogram is one of them, and has been of great interest since the early development of MRI in the mid 80’s. Diffusion Tensor Imaging, also known as DTI, has been actively studied for over the last two decades or so, and succeeded in obtaining markedly improved representations of the fiber or white matter tracts of the human nervous system both in-vivo as well as with cadaver brain. White matter tractography, however, suffered a number of difficulties such as shortcoming in detection of fiber crossings and detection of small fibers mainly due to the limited sensitivity, resolution, and the techniques commonly used today.
Improvements to the spatial resolution and the sensitivity of white matter tractography, therefore, require high sensitivity as well as new tractographic techniques for the better visualization of the fine details of the fiber density as well as their distributions in the human brain. In this respect, two important developments have been emerged in this field, namely ultra-high field (UHF) MRI such as 7.0T MRI and the new image post-processing technique known as Track Density Imaging (TDI). These two developments are the two major components of the new white matter imaging atlas of the present book. In this book, we have improved the imaging of white matter by advancement of the two major aspects mentioned earlier, namely improvement of the sensitivity and resolution by using the UHF 7.0T MRI and newly developed super resolution white matter track density imaging technique, the Super Resolution TDI technique.
We believe this new book represents the result of these two new major developments, that is, the higher resolution and higher sensitivity image improvement, and even further resolution improvement from the super-resolution tractography-based technique. These two improvements allowed us to visualize in-vivo the human nervous system with the finest resolution and sensitivity, which should have wide ranging implications, from the study of human brain diseases such as multiple sclerosis to Alzheimer’s disease and functional connectivity study in modern neuroscience.
In addition to the two improvements, the present white matter atlas is further enhanced by incorporation of the ultra-high resolution anatomical images of 7.0T MRI, which were obtained simultaneously with the TDI image data, and assisted us to identify the tracks and fibers in relation to the anatomical landmark structures, such as AC (Anterior Commissure) and PC (Posterior Commissure) or the mammillary body.
We hope this new book will be a useful addition to the field of brain research as well as to the clinical setting, such as for the “Human Connectome” project and for the diagnosis of various neurological diseases such as multiple sclerosis and Alzheimer’s disease.
Zang-Hee Cho, Ph.D, Editor
Fernando Calamante, Ph.D, Co-Editor
* Foreword
Recent advances in neuroimaging, especially the advancement of the newly emerging tools and technology such as the ultra-high field MRI brought about revolution in the fields of medical imaging and neuro-anatomy.
This “Human Brain White Matter Atlas” is the product of the new 7.0T MRI technology with new TDI (Track Density Imaging) technique with superb knowledge on human neuroanatomy and, for the first time, began to show vividly in-vivo human fiber tracts of the finest details such as the medial forebrain bundle (MFB) never before possible. These images will assist not only the neuroscientist but also many clinicians in the areas from neurology and neurosurgery to psychiatry.
This book is also a new white matter track reference book for the students, and other academic personnel for the research as well as clinical arena, and has been edited by a team of experts in neuroscience and anatomy at Neuroscience Research Institute, Gachon University, Korea, in cooperation with the Florey Neuroscience Institutes, University of Melbourne, Australia.
Authors of the book are the frontiers of each specialized field, from MRI imaging and image processing technology to the brain anatomy.
This book, for the first time, began to visualize the inner fiber structures of the thalamus as well as many small fibers, such as the fasciculus retroflexus, mammillotegmental tract, and ansa peduncularis in the brain hitherto difficult to capture with conventional DTI at lower field MRI such as 1.5T or 3.0T MRI.
I feel it would be a timely publication considering the fact that there is an increasing demand of human brain tractography and connectivity research worldwide as well as numerous clinical demands in many neurological diseases and disorders such as multiple sclerosis and vascular dementia including treatment in neurological and psychiatric disorders using new tools such as the deep brain stimulation (DBS).
For the readers, not only the white matter atlas but also the corresponding anatomical images are shown for reference. The latter would be a useful guide for the analysis and correlation study to the white matter track displayed in this book. Note that both the anatomical images and white matter atlas are from the same subject, therefore, it would be easy and accurate for the correlation study.
I am sure this white matter atlas is the first of its kind with the highest resolution ever obtained using the latest technologies such as 7.0T MRI with advanced artifact corrections such as the susceptibility artifact correction and TDI tractography data processing.
I sincerely hope that this book would serve as an important and useful reference book for the years to come.
Kil Soo Choi, MD Professor Emeritus, Seoul National University
&
Former Vice President of the World Federation of Neurosurgical Societies (WFNS)
* Preface
One of the most important advances in the field of neuroscience and brain related research is the development of the visualizing the human nervous system or white matter tracts in-vivo. MRI white matter tractography and track densitogram is one of them, and has been of great interest since the early development of MRI in the mid 80’s. Diffusion Tensor Imaging, also known as DTI, has been actively studied for over the last two decades and succeeded in obtaining markedly improved representations of the fiber or white matter tracts of the human nervous system both in-vivo as well as with cadaver brain. White matter tractography, however, suffered a number of difficulties such as shortcoming in detection of fiber crossings and detection of small fibers mainly due to the limited sensitivity and the techniques commonly used today.
Improvements to the spatial resolution and the sensitivity of white matter tractography, therefore, require high sensitivity as well as new tractographic techniques for the better visualization of the fine details of the fiber density as well as their distributions in the human brain. In this respect, recently two important developments have been emerged in this field, namely ultra-high field (UHF) MRI such as 7.0T MRI and the new image post-processing technique known as Track Density Imaging or Super Resolution TDI. These two developments are the two major components of the new white matter imaging atlas book we have presented in this volume. In this book, we have improved the imaging of white matter by advancement of the two major aspects mentioned earlier, namely improvement of the sensitivity and resolution by using the UHF 7.0T MRI and newly developed super resolution white matter track density imaging technique, the Super Resolution TDI technique.
We believed this new book represents these two new major developments, that is, the visualization of in-vivo human brain nervous system with the finest resolution and sensitivity, which should have wide ranging implications, from the study of human brain diseases such as multiple sclerosis to Alzheimer’s disease to the modern neuroscience such as the functional connectivity.
In addition to the two improvements, the present white matter atlas book is further enhanced by incorporating the ultra-high resolution anatomical images of 7.0T MRI, which were obtained simultaneously with the TDI image data. The latter greatly enhanced our interpretation of the tractography-based images, and vice versa.
We hope this new book will be a useful addition to the field of brain research as well as to the clinical setting, such as for the “Human Connectome” project and for the diagnosis of various neurological diseases such as multiple sclerosis and Alzheimer’s disease.
Zang-Hee Cho, Ph.D, Editor
Fernando Calamante, Ph.D, Co-Editor
Je-Geun Chi, MD & Ph.D, Co-Editor
Je-Geun Chi, MD & Ph.D, Co-Editor
* Introduction
Nothing defines the function of a neuron better than its connections. What ultimately determines the vast difference in their function is not only their molecular profile but also their structural connectivity. The recent development of diffusion tensor imaging (DTI) has made it possible to identify in vivo some details of organizations within the major white matter pathways, both in normal brains and in clinical situations in which the pathways are damaged. For instance, for primary progressive aphasia, diffusion tensor imaging highlights the tracts that are damaged, demonstrating its potential value as a new tool in the multimodal diagnostic evaluation.
Knowledge of the location of the cerebral insult is of prime importance to determine the cause of the disorder. It is also important to realize that a lesion of the cortex destroys more than just the cortical area involved: it also affects the afferent and efferent cortical fibers. Therefore, stereotactic white matter atlases are needed not only for precise targeting in functional neurosurgery, but also for accurate localization of therapeutic lesions or the site of stimulation (microelectrode recordings, etc) as well as localization of vascular damages. We have to realize, however, that these new imaging techniques are based on a priori hypotheses derived from earlier anatomical observations regarding the course of the fiber bundles particularly for the association fiber pathways in adult brains. Therefore all the information that could be obtained through diffusion tensor imaging should be carefully compared and verified.
We observed many interesting findings in this 7.0T tractography-based work that have not been visible in vivo previously. They are stria longitudinalis, brachium of superior and inferior colliculus, fasciculus retroflexus, dorsal longitudinal fasciculus/medial forebrain bundle, and ansa pedundularis, among others. We also found that there are significant amount of fibers running anteroposteriorly around the massa intermedia and septum pellucidum as well as the thalamus. It was interesting to note that the optic chiasm is invisible in coronal plane although it is well visualized on sagittal and axial planes. Another prominent structure seen in tractography was stratum zonale on the top of the thalamus. Many transversely running fibers are seen in the pulvinar nucleus as well. In this atlas, ansa peduncularis appears in many slices, particularly in coronal sections below the anterior commissure. This is a complex fiber bundle curving around the medial edge of the internal capsule and connecting the anterior part of the temporal lobe, the amygdaloid nucleus, the olfactory cortex, and possibly even the thalamus
Reference System
Despite the remarkable images provided by CT and MRI, numerous cerebral structures are not yet visible by radiologic diagnostic techniques. Therefore, the indirect localization, which requires the use of a system of reference, is still necessary to complete the interpretation of neuroradiological images.
We have emphasized in our previous Atlas (7.0Tesla MRI Brain Atlas, Cho ed.) that it would be more reasonable to use central intercommissural line (ClL) for the reference system of the brain imaging in this era of high resolution. CIL is the line passing through the center of the anterior commissure (AC) and posterior commissure (PC), in comparison with Talairach reference system which uses tangential intercommissural line (TCL), that passes through the upper border of the AC and lower border of the PC. There is approximately 10 degree difference between ICL and TCL, which makes almost 1 cm difference if one plots them on the cortical surface. Furthermore, we have proposed the midpoint of the AC and PC to be the center of their brain coordinate system since it is readily visible with 7.0T MRI images. It is certainly easy to find this center and utilize it for the base point of coronal, sagittal and axial images.
We applied this system in present white matter atlas as we did in our previous gray matter atlas (7.0Tesla MRI Brain Atlas, Cho ed.) published previously. With this system the possibility of establishing a standard or normalized orthogonal grid could allow development of an anatomico-electroclinical correlations. We hope this system would also be valid statistically for all brains, regardless of their individual dimensions or proportions.
All the images shown in this atlas are of real scale. Both MRI and TDI images are displayed on the opposing page and are obtained from the same subject who is a 32 years old healthy right handed male. The reference brain used in this Atlas is the cadaver brain that was utilized in our previous atlas (7.0Tesla Brain Atlas, Cho ed.). Again, therefore, the relative adjustment unit (RAU) shown in the parentheses represents the cadaver brain data.
Terminology, labeling, and abbreviation
Different authors refer to the same brain structure with different names. In this atlas, in an attempt to use the most up-to-date anatomical terminology, we have adopted the standard terms used in “Terminologia Anatomica” by the International Federation of Associations of Anatomists published in 1998. It supersedes the previous standards described in “Nomina Anatomica.” Exceptions are fusiform gyrus instead of occipito-temporal gyrus and fronto-occipital fasciculus instead of occipito-frontal fasciculus. The gyrus is usually defined by a ridge or convolution on the surface of cerebral hemisphere generally surrounded by one or more sulci. It includes both gray matter (cortex) and white matter (gyral white matter). We labeled this gyral white matter as a specific gyrus. This labelling is different from the convention that defines the gyrus to be cortex (gyral gray matter) instead of whole gyrus covering both gray and white matter of the gyrus.
Many commonly used positional and directional notations are abbreviated. In most instances the initial letters of the structures are capitalized. For example, SFG is the abbreviation for superior frontal gyrus, SLF for superior longitudinal fasciculus, MTT for mammillothalamic tract and ST for stria terminalis, etc. Some modifications are made for the same initials but with different structures, like CC for corpus callosum vs. CrC for crus cerebri, CS for cingulate sulcus vs. CeS for central sulcus, and PrG for precentral gyrus vs. PoG for postcentral gyrus.
All identifiable anatomical structures were labeled on the images of both the MRI and TDI brain. For the TDI, it was intended to label primarily gray matter structures in the right side of the image while most of the white matter structures are given in the left, particularly in coronal and axial sections. When the structures shown in the image are different from the right and left, such as the case of sagittal view images, they were labeled in both sides. Structures that appeared more than once were designated with numbers. As such, this atlas defines not only the core white matter structures, but also the superficial white matter, the deep gray matter, as well as the cortex. In this atlas we have not used the term ‘sagittal stratum (SS)’. This term is ambiguous and has been used to designate different structure in the literature. The SS is generally thought of as being synonymous with the optic radiation, however, the question as to whether the SS is a projection system, an association pathway, or both, is not yet settled.
In the recent white matter atlas book by Oishi et al. (Oishi K et al., 2010, MRI Atlas of Human White Matter, 2nd Ed, London, Burlington and San Diego, Academic Press), the sagittal stratum (SS) includes the inferior longitudinal fasciculus and inferior fronto-occipital fasciculus. However, Schmahmann et al. (Schmahmann JD and Pandya DN, 2006, Fiber Pathways of the Brain, New York, Oxford University Press) describe the SS as unrelated to the association fibers in the superior and inferior longitudinal fasciculi but rather a strictly cortico-subcortical projection system. It includes the Meyer’s loop in the rostral sector, the optic radiation of the temporal lobe in the ventral region, and the occipital lobe in the caudal region. It conveys fibers from the parietal, temporal, and occipital lobes in a topographically arranged fashion to the thalamus and brainstem, including the nuclei of the basis pontis. For the names of the thalamic nuclei, the terminology used in this Atlas follows closely the terminology used in Morel’s book (Morel A, 2007, Stereotactic Atlas of the Human Thalamus and Basal Ganglia, New York, Informa Healthcare)
