Faro SH, Mohamed FB, eds. BOLD fMRI: A Guide to Functional Imaging for Neuroscientists. Springer 2010, 291 pages, 79 illustrations, $49.95.
The book BOLD fMRI, edited by S. H. Faro and F. B. Mohamed, is a collection of 11 of the 20 review articles previously published in the book Functional MRI: Basic Principles and Clinical Applications, edited by the same editors and copyrighted 2006 by the same publisher. According to the editors, the selected articles are expected to be of particular interest to neuroscientists, and the focus of the selection is basic principles of BOLD imaging. The page layout is changed, but no revision is noted.
In MRI, the blood-oxygenation-level-dependent (BOLD) effect refers to the phenomenon that the paramagnetism of blood is closely correlated with the oxygen saturation level of hemoglobin. The saturation level, which can be modulated by neuronal activity, alters the regional paramagnetism and, hence, the relaxation times of the magnetization of blood and the transverse relaxation time of the magnetization of tissue in the vicinity of blood vessels. The BOLD effect can be conveniently detected by T2*-weighted MRI. Nowadays, T2*-weighted MRI and BOLD have been used synonymously in many publications, including this book. However, T2*-weighted MRI can also be influenced by, for example, the hydrogen nucleus density and diffusivity in addition to the BOLD effect and is not the only method for MR imaging of the brain function, but T2*-weighted MRI is the method that is covered in this book and in its original edition. The scope of both editions is functional MRI (fMRI) of the brain, although the BOLD effect has been utilized for functional imaging of various organs.
The articles are written by independent authors in the style of journal review articles but are more than just bibliographical reviews; they are written to introduce a field of study to the reader and to summarize the advancement. An extensive bibliography of original research papers companions each article. A prerequisite for the book is some experience or knowledge of how fMRI is conventionally performed; that is, a T2*-weighted MR image is taken every few seconds in a scan session in which the scanned subject is presented with cognitive challenges or is cued to perform some tasks, such as memory retrieval, photos of different facial expressions, tapping fingers, passively viewing a varying pattern. Analyzing the sequence of images pixel by pixel, one expects to find the image pixel intensity changes in accordance with the timing of the challenges or tasks at the brain locations that are involved. With this simple idea of the conventional fMRI scan in mind, this book describes the mechanism of the pixel intensity change related to the BOLD effect, the relationship between the BOLD effect and the neuronal activation, and research and health-related applications of fMRI. The book assumes the reader is already familiar with the MRI scanner, which is, of course, not an issue to a neuroradiologist. The figures are properly reproduced.
Part I contains five articles that describe the BOLD effect and its coupling to the neuronal activity induced by functional stimuli (by S.-G. Kim and P.A. Bandettini), the basic MRI physics and imaging principles (by A.B. Pinus and F.B. Mohamed), fMRI experiment design and data analysis (by G.K. Aguirre), challenges and limitations of fMRI (by R.T. Constable), and clinical challenges (by N. Pouratian and S.Y. Bookheimer). This part reviews the general aspects of the fMRI technology. The article on MRI physics is very dense; it is probably better used as a refresher for readers who already have some exposure to the theory of operation of MRI.
Part II is entitled “fMRI Clinical Application”; it contains five articles that describe the use of fMRI in: neurosurgery and cognitive studies (by J. Hirsch), memory in aging and dementia (by A.J. Saykin and H.A. Wishart), language systems (by J.R. Binder), the Wada test (by B.C. McDonald, A.J. Saykin, J.M. Williams, and B.A. Assaf), and cognitive research (by M. D’Esposito). Each article provides in-depth background of the methodology and balanced discussion on the advantages, challenges, and limitations of the use of fMRI. Most of the material covered is still experimental but should be of interest to medical imaging research scientists and physicians.
Part III is an article by the editors entitled “Neuroanatomical Atlas.” The article presents a series of 22 fMRI activation maps (i.e., colored pixels overlaid on brain MRI images to indicate activation) which are intended to serve as a reference or template for fMRI users. Each map contains three views (axial, coronal, and sagittal) and is either captioned with the name of the body part involved in a motor task (e.g., hand, face, knee, trunk) or the name of the neuroanatomical or functional location activated by visual, auditory, or language function (e.g., superior frontal gyrus, Broca’s motor area, object naming task). The scan and experimental conditions and the tasks to induce the activations are briefly mentioned but are not sufficient for a reader to reproduce these activations. No annotation or discussion is provided. These maps are apparently obtained from a single subject, not an averaged representation of a population.
The articles that are omitted from the original edition are fMRI in: psychiatry application, epilepsy, visual pathways, auditory cortex, pediatric applications, clinical pain, pharmacological applications, and cognitive neuroscience. These omitted articles would fit the scope of the new edition well and could be of interest to neuroscientists. A concluding article by the editors on clinical overview and future fMRI applications, as well as an appendix on the independent component analysis, are also excluded. The article on experimental design and data analysis, unfortunately, refers the reader to the excluded appendix. In a few places, the chapter and page numbers are not updated.
This is not a new book, nor an updated edition; the latest references cited are of 2004. Thus the book does not cover the recent concepts of notable importance in the advancement of T2*-weighted fMRI, such as the resting-state (i.e., fMRI scan without stimulus), identification of synchronized activities in different parts of the brain (i.e., connectivity), fMRI in CNS drug development, activation signal calibration, and quantitative fMRI.
Because fMRI does not detect the neuronal activity directly but the hemodynamic change (i.e., the change of the BOLD effect), it is particularly important to understand the principles, image contrast mechanism, and limitations of fMRI for proper experiment design and result interpretation and to avoid flaws. This book can be a choice to fill in the background knowledge and be used as a reference. The book is not intended to be an instruction manual or a hands-on how-to book to help readers start with fMRI data collection, image processing, or the statistical analysis. Instead, the book’s theme is about the science and experiments of fMRI. A reader who has some experience in fMRI and is interested in the fundamentals or exploring different areas of fMRI application can benefit from this concise overview and the bibliographies.
