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An approach to MRI-based dosimetry for transcranial magnetic stimulation

NEUROimage 2007年第4期36卷 1171-1178页

作者： Hernandez-Garcia, Luis Lee, Sangwoo Grissom, William Funct MRI Lab Ann Arbor MI 48109 USA

A new MRI-based measurement of the magnetic vector field distribution generated by a transcranial magnetic stimulation (TMS) probe is introduced in this study. Projections of the static magnetic field produced by a DC current in a TMS probe onto the axis of the scanner's main field (B-0) can be measured using a conventional B-0 field-mapping technique. The remaining Cartesian components can then be calculated from projections obtained at different orientations of the sample and probe. The measured static field can then be scaled to calculate the effects of a dynamic TMS pulse. This article includes a study demonstrating the feasibility of this approach on a phantom and a human subject. (C) 2007 Elsevier Inc. All rights reserved.

关键词： Artifacts Brain Mapping/methods Brain Mapping/methods Cerebral Cortex/physiology computer Simulation Electromagnetic Fields Electromagnetic Fields Humans image processing, computer-assisted/methods Magnetic Resonance Imaging/methods Phantoms, Imaging Software Transcranial Magnetic Stimulation/methods

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Longitudinal and cross-sectional analysis of atrophy in Alzheimer's disease: Cross-validation of BSI, SIENA and SIENAX

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NEUROimage 2007年第4期36卷 1200-1206页

作者： Smith, Stephen M. Rao, Anil De Stefano, Nicola Jenkinson, Mark Schott, Jonathan M. Matthews, Paul M. Fox, Nick C. Univ Oxford Ctr Funct MRI Brain Oxford England GlaxoSmithKline Clin Imaging Ctr Hammersmith England Univ Siena Dept Neurol & Behav Sci I-53100 Siena Italy UCL Inst Neurol Dementia Res Ctr London WC1E 6BT England

Brain volume loss (atrophy) is widely used as a marker of disease progression. Atrophy has been measured with a variety of methods, some estimating atrophy rate from two temporally separated scans, and others estimating atrophy state from a single scan. Three popular tools for measuring brain atrophy are BSI and SIENA (rate) and SIENAX (state). Previous papers have shown BSI and SIENA to have similar accuracy, but no work has carefully compared both methods using the same data set. Here we compare these methods, using data from patients with Alzheimer's disease and age-matched controls. We also compare the SIENA longitudinal measure with atrophy state estimated by SIENAX using just the earliest scan taken from each subject. We show strong correspondence and similar sensitivity to atrophy between all 3 measures. (C) 2007 Elsevier Inc. All rights reserved.

关键词： Aged Alzheimer Disease/diagnosis Artifacts Artificial Intelligence Atrophy Brain/pathology Cerebral Ventricles/pathology Cross-Sectional Studies Female Humans image processing, computer-assisted/methods Longitudinal Studies Magnetic Resonance Imaging/methods Male Reference Values Sensitivity and Specificity Software

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A component based noise correction method (CompCor) for BOLD and perfusion based fMRI

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NEUROimage 2007年第1期37卷 90-101页

作者： Behzadi, Yashar Restom, Khaled Liau, Joy Liu, Thomas T. Univ Calif San Diego Ctr Funct Magnet Resonance Imaging La Jolla CA 92093 USA Univ Calif San Diego Dept Radiol La Jolla CA 92093 USA Univ Calif San Diego Dept Bioengn La Jolla CA 92093 USA

A component based method (CompCor) for the reduction of noise in both blood oxygenation level-dependent (BOLD) and perfusion-based functional magnetic resonance imaging (fMRI) data is presented. In the proposed method, significant principal components are derived from noise regions-of-interest (ROI) in which the time series data are unlikely to be modulated by neural activity. These components are then included as nuisance parameters within general linear models for BOLD and perfusion-based fMRI time series data. Two approaches for the determination of the noise ROI are considered. The first method uses high-resolution anatomical data to define a region of interest composed primarily of white matter and cerebrospinal fluid, while the second method defines a region based upon the temporal standard deviation of the time series data. With the application of CompCor, the temporal standard deviation of resting-state perfusion and BOLD data in gray matter regions was significantly reduced as compared to either no correction or the application of a previously described retrospective image based correction scheme (RETROICOR). For both functional perfusion and BOLD data, the application of CompCor significantly increased the number of activated voxels as compared to no correction. In addition, for functional BOLD data, there were significantly more activated voxels detected with CompCor as compared to RETROICOR. In comparison to RETROICOR, CompCor has the advantage of not requiring external monitoring of physiological fluctuations. (c) 2007 Elsevier Inc. All rights reserved.

关键词： Adult Algorithms Artifacts Cerebral Cortex/blood supply Cerebral Cortex/physiology Energy Metabolism/physiology Fourier Analysis Fourier Analysis Humans image Enhancement/methods image processing, computer-assisted/methods Linear Models Magnetic Resonance Imaging/methods Oxygen/blood Photic Stimulation Principal Component Analysis Regional Blood Flow/physiology Software Visual Perception/physiology

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Integrating VBM into the general linear model with voxelwise anatomical covariates

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NEUROimage 2007年第2期34卷 500-508页

作者： Oakes, Terrence R. Fox, Andrew S. Johnstone, Tom Chung, Moo K. Kalin, Ned Davidson, Richard J. Univ Wisconsin Waisman Ctr Waisman Lab Brain Imaging & Behav Madison WI 53705 USA Univ Wisconsin Dept Psychol Madison WI 53706 USA Univ Wisconsin Dept Stat Madison WI 53706 USA Univ Wisconsin Dept Psychiat Madison WI 53706 USA

A current limitation for imaging of brain function is the potential confound of anatomical differences or registration error, which may manifest via apparent functional "activation" for between-subject analyses. With respect to functional activations, underlying tissue mismatches can be regarded as a nuisance variable. We propose adding the probability of gray matter at a given voxel as a covariate (nuisance variable) in the analysis of voxelwise multisubject functional data using standard statistical techniques. A method is presented to assess the extent to which a functional activation can reliably be explained by underlying anatomical differences, and simultaneously, to assess the component of the functional activation which cannot be attributed to anatomical difference and thus is likely due to functional difference alone. Extension of the method to other intermodal imaging applications is discussed. Two exemplary data sets, one PET and one fMRI, are used to demonstrate the implementation and utility of this method, which apportions the relative contributions of anatomy and function for an apparent functional activation. The examples show two distinct types of results. First, a so-called functional activation may actually be caused by a systematic anatomical difference which, when modeled, diminishes the functional effect. In the second result type, including the anatomical differences in the model can account for a large component of otherwise unmodeled variance, yielding an increase in the functional effect cluster size and/or magnitude. In either case, ignoring the readily available structural information can lead to misinterpretation of functional results. (c) 2006 Elsevier Inc. All rights reserved.

关键词： Brain/anatomy & histology Brain Mapping Brain Mapping Diagnostic Imaging Humans image processing, computer-assisted/methods Magnetic Resonance Imaging Positron-Emission Tomography

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EchoComTEE - a simulator for transoesophageal echocardiography

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ANAESTHESIA 2007年第4期62卷 347-353页

作者： Weidenbach, M. Drachsler, H. Wild, F. Kreutter, S. Razek, V. Grunst, G. Ender, J. Berlage, T. Janousek, J. Univ Leipzig Ctr Heart Dept Paediat Cardiol D-04289 Leipzig Germany Univ Leipzig Ctr Heart Dept Anaesthesiol D-04289 Leipzig Germany Fraunhofer Inst Appl Informat Technol D-53754 St Augustin Germany

Transoesophageal echocardiography (TOE) requires extensive hands-on training, and it is for this purpose we have designed EchoComTEE, a simulator for TOE. It consists of a manikin and dummy probe;according to the position of the dummy probe (tracked by an electromagnetic sensor), two-dimensional (2D) images are calculated from three-dimensional (3D) data sets. Echo cardiographic images are presented side-by-side with a virtual scene consisting of a 3D heart, probe tip and image plane. In this way the trainee is provided with visual feed-back of the relationship between echocardiogram and image plane position. We evaluated the simulator using a standardised questionnaire. Twenty-five experts and 31 novice users participated in the study. Most experts graded the simulator as realistic and all recommended its use for training. Most novice users felt the simulator supported spatial orientation during TOE and, as anaesthetists often do not have training in transthoracic echo cardiography, in this group the TOE simulator might be particularly useful.

关键词： Anesthesiology/education Attitude of Health Personnel Clinical Competence Echocardiography, Transesophageal/standards Echocardiography, Transesophageal/standards Education, Medical, Continuing/methods Feedback Humans image processing, computer-assisted/methods Imaging, Three-Dimensional/methods Manikins Teaching Materials

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Continuous carry-over designs for fMRI

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NEUROimage 2007年第4期35卷 1480-1494页

作者： Aguirre, Geoffrey Karl Univ Penn Dept Neurol Philadelphia PA 19104 USA

This paper describes continuous carry-over fMRI experiments. In these studies, stimuli are presented in an unbroken, sequential manner, and can be used to estimate simultaneously the mean difference in neural activity between stimuli as well as the effect of one stimulus upon another (carry-over effects). Neural adaptation, which has been the basis of many recent fMRI studies, is shown to be a specific form of carry-over effect. With this approach, the adapting effects of stimuli may be studied in a continuous sequence, as opposed to within isolated pairs or blocks. Additionally, the average, direct effect of a stimulus upon neural response can form the basis of a simultaneously obtained distributed pattern analysis, allowing comparison of neural population coding on focal (within voxel) and distributed (across voxel) spatial scales. These studies are ideally conducted with serially balanced sequences, in which every stimulus precedes and follows every other stimulus. While m-sequences can provide this stimulus order, the type I index I sequence of Finney and Outhwaite may be used in fMRI studies for those experimental designs for which an m-sequence solution does not exist. Continuous carry-over designs with serially balanced sequences are argued to be particularly well suited to the characterization of "similarity spaces," in which the perceptual similarity of stimuli is related to the structure of neural representation both within and across voxels. These concepts are illustrated with a worked example involving the neural representation of color. It is shown that data from a single scanning session are sufficient to detect direct and carry-over effects, as well as demonstrate the correspondence of the similarity structure of distributed patterns of neural firing and the perceptual similarity of a set of colors. (c) 2007 Elsevier Inc. All rights reserved.

关键词： Adaptation, Physiological/physiology Adult Brain/physiology Color Perception/physiology Data Interpretation, Statistical Female Humans image processing, computer-assisted/methods Linear Models Magnetic Resonance Imaging/methods Magnetic Resonance Imaging/statistics & numerical data Neurons/physiology Oxygen/blood Photic Stimulation Physical Stimulation Psychomotor Performance/physiology

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A Bayesian framework for global tractography

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NEUROimage 2007年第1期37卷 116-129页

作者： Jbabdi, S. Woolrich, M. W. Andersson, J. L. R. Behrens, T. E. J. Univ Oxford John Radcliffe Hosp FMRIB Oxford OX3 9DU England Univ Oxford Dept Expt Psychol Oxford England

We readdress the diffusion tractography problem in a global and probabilistic manner. Instead of tracking through local orientations, we parameterise the connexions between brain regions at a global level, and then infer on global and local parameters simultaneously in a Bayesian framework. This approach offers a number of important benefits. The global nature of the tractography reduces sensitivity to local noise and modelling errors. By constraining tractography to ensure a connexion is found, and then inferring on the exact location of the connexion, we increase the robustness of connectivity-based parcellations, allowing parcellations of connexions that were previously invisible to tractography. The Bayesian framework allows a direct comparison of the evidence for connecting and non-connecting models, to test whether the connexion is supported by the data. Crucially, by explicit parameterisation of the connexion between brain regions, we infer on a parameter that is shared with models of functional connectivity. This model is a first step toward the joint inference on functional and anatomical connectivity. (c) 2007 Elsevier Inc. All rights reserved.

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Effects of diffusion weighting schemes on the reproducibility of DTI-derived fractional anisotropy, mean diffusivity, and principal eigenvector measurements at 1.5T

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NEUROimage 2007年第4期36卷 1123-1138页

作者： Landman, Bennett A. Farrell, Jonathan A. D. Jones, Craig K. Smith, Seth A. Prince, Jerry L. Mori, Susumu Johns Hopkins Univ Sch Med Russell H Morgan Dept Radiol & Radiol Sci Baltimore MD 21205 USA Johns Hopkins Univ Sch Med Dept Biomed Engn Baltimore MD 21205 USA Kennedy Krieger Inst FM Kirby Res Ctr Funct Brain Imaging Baltimore MD 21205 USA Johns Hopkins Univ Sch Med Dept Biophys & Biophys Chem Baltimore MD 21205 USA Johns Hopkins Univ Dept Elect & Comp Engn Baltimore MD 21205 USA

Diffusion tensor imaging (DTI) is used to study tissue composition and architecture in vivo. To increase the signal to noise ratio (SNR) of DTI contrasts, studies typically use more than the minimum of 6 diffusion weighting (DW) directions or acquire repeated observations of the same set of DW directions. Simulation-based studies have sought to optimize DTI acquisitions and suggest that increasing the directional resolution of a DTI dataset (i.e., the number of distinct directions) is preferable to repeating observations, in an equal scan time comparison. However, it is not always clear how to translate these recommendations into practice when considering physiological noise and scanner stability. Furthermore, the effect of different DW schemes on ht vivo DTI findings is not fully understood. This study characterizes how the makeup of a DW scheme, in terms of the number of directions, impacts the precision and accuracy of in vivo fractional anisotropy (FA), mean diffusivity, (MD), and principal eigenvector (PEV) findings. Orientation dependence of DTI reliability is demonstrated in vivo and a principled theoretical framework is provided to support and interpret findings with simulation results. As long as sampling orientations are well balanced, differences in DTI contrasts due to different DW schemes are shown to be small relative to intra-session variability. These differences are accentuated at low SNR, while minimized at high SNR. This result suggests that typical clinical studies, which use similar protocols but different ell-balanced DW schemes, are readily comparable within the experimental precision. (C) 2007 Elsevier Inc. All rights reserved.

关键词： Adult Anisotropy Artifacts Brain/anatomy & histology computer Simulation Diffusion Magnetic Resonance Imaging/methods Humans image processing, computer-assisted/methods Male Monte Carlo Method Sensitivity and Specificity Software

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Multivariate examination of brain abnormality using both structural and functional MRI

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NEUROimage 2007年第4期36卷 1189-1199页

作者： Fan, Yong Rao, Hengyi Hurt, Hallam Giannetta, Joan Korczykowski, Marc Shera, David Avants, Brian B. Gee, James C. Wang, Jiongjiong Shen, Dinggang Univ Penn Dept Radiol Philadelphia PA 19104 USA Univ Penn Ctr Funct Neuroimaging Dept Neurol Philadelphia PA 19104 USA Childrens Hosp Philadelphia Dept Pediat Div Neonatol Philadelphia PA 19104 USA

A multivariate classification approach has been presented to examine the brain abnormalities, i.e., due to prenatal cocaine exposure, using both structural and functional brain images. First, a regional statistical feature extraction scheme was adopted to capture discriminative features from voxel-wise morphometric and functional representations of brain images, in order to reduce the dimensionality of the features used for classification, as well as to achieve the robustness to registration error and inter-subject variations. Then, this feature extraction method was used in conjunction with a hybrid feature selection method and a nonlinear support vector machine for the classification of brain abnormalities. This brain classification approach has been applied to detecting the brain abnormality associated with prenatal cocaine exposure in adolescents. A promising classification performance was achieved on a data set of 49 subjects (24 normal and 25 prenatally. cocaine-exposed teenagers), with a leave-one-out cross-validation. Experimental results demonstrated the efficacy of our method, as well as the importance of incorporating both structural and functional images for brain classification. Moreover, spatial patterns of group difference derived front the constructed classifier were mostly consistent with the results of the conventional statistical analysis method. Therefore, the proposed approach provided not only a multivariate classification method for detecting brain abnormalities, but also an alternative way for group analysis of multimodality images. (C) 2007 Elsevier Inc. All rights reserved.

关键词： Adolescent Algorithms Artificial Intelligence Brain/drug effects Brain/pathology Brain/physiopathology Cocaine/toxicity Female Humans image Enhancement/methods image processing, computer-assisted/methods Magnetic Resonance Imaging/methods Multivariate Analysis Nonlinear Dynamics Pregnancy Prenatal Exposure Delayed Effects Sensitivity and Specificity Software Street Drugs/toxicity

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Hybrid diffusion imaging

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NEUROimage 2007年第3期36卷 617-629页

作者： Wu, Yu-Chien Alexander, Andrew L. Univ Wisconsin Waisman Ctr Waisman Lab Brain Imaging & Behav Madison WI 53705 USA Univ Wisconsin Dept Radiol Madison WI 53706 USA Univ Wisconsin Dept Med Phys Madison WI 53706 USA Univ Wisconsin Dept Psychiat Madison WI 53706 USA

Diffusion measurements in the human central nervous system are complex to characterize and a broad spectrum of methods have been proposed. In this study, a comprehensive diffusion encoding and analysis approach, hybrid diffusion imaging (HYDI), is described. The HYDI encoding scheme is composed of multiple concentric "shells" of constant diffusion weighting, which may be used to characterize the signal behavior with low, moderate and high diffusion weighting. HYDI facilitates the application of multiple data analyses strategies including diffusion tensor imaging (DTI), multi-exponential diffusion measurements, diffusion spectrum imaging (DSI) and q-ball imaging (QBI). These different analysis strategies may provide complementary information. DTI measures (mean diffusivity and fractional anisotropy) may be estimated from either data in the inner shells or the entire HYDI data. Fast and slow diffusivities were estimated using a nonlinear least squares bi-exponential fit on geometric means of the HYDI shells. DSI measurements from the entire HYDI data yield empirical model-independent diffusion information and are well-suited for characterizing tissue regions with complex diffusion behavior. DSI measurements were characterized using the zero displacement probability and the mean-squared displacement. The outermost HYDI shell was analyzed using QBI analysis to estimate the orientation distribution function (ODF), which is useful for characterizing the directions of multiple fiber groups within a voxel. In this study, an HYDI encoding scheme with 102 diffusion-weighted measurements was obtained over most of the human cerebrum in under 30 min. (c) 2007 Elsevier Inc. All rights reserved.

关键词： Algorithms Brain/anatomy & histology computer Simulation Data Interpretation, Statistical Diffusion Magnetic Resonance Imaging/methods Diffusion Magnetic Resonance Imaging/statistics & numerical data Humans image processing, computer-assisted/methods image processing, computer-assisted/statistics & numerical data Nerve Fibers/physiology

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