Cerebro-Cerebellar Pathways for Verbal Working Memory

The current study examined the structural and functional connectivity of the cerebro-cerebellar network of verbal working memory as proposed by Chen and Desmond (2005a). Diffusion spectrum imaging was employed to establish structural connectivity between cerebro-cerebellar regions co-activated during a verbal working memory task. The inferior frontal gyrus, inferior parietal lobule, pons, thalamus, superior cerebellum and inferior cerebellum were used as regions of interest to reconstruct and segment the contralateral white matter cerebro-cerebellar circuitry. The segmented pathways were examined further to establish the relationship between structural and effective connectivity as well as the relationship between structural connectivity and verbal working memory performance. No direct relationship between structural and effective connectivity was found but the results demonstrated that structural connectivity is indirectly related to effective connectivity as DCM models that resembled more closely with underlying white matter pathways had a higher degree of model inference confidence. Additionally, it was demonstrated that the structural connectivity of the ponto-cerebellar tract was associated with individual differences in response time for verbal working memory. The findings of the study contribute to further our understanding of the relationship between structural and functional connectivity and the impact of variability in verbal working memory performance

Frequency Dependent Alterations in Regional Homogeneity of Baseline Brain Activity in Schizophrenia

Low frequency oscillations are essential in cognitive function impairment in schizophrenia. While functional connectivity can reveal the synchronization between distant brain regions, the regional abnormalities in task-independent baseline brain activity are less clear, especially in specific frequency bands. Here, we used a regional homogeneity (ReHo) method combined with resting-state functional magnetic resonance imaging to investigate low frequency spontaneous neural activity in the three different frequency bands (slow-5:0.01–0.027 Hz; slow-4:0.027–0.08 Hz; and typical band: 0.01–0.08 Hz) in 69 patients with schizophrenia and 62 healthy controls. Compared with controls, schizophrenia patients exhibited decreased ReHo in the precentral gyrus, middle occipital gyrus, and posterior insula, whereas increased ReHo in the medial prefrontal cortex and anterior insula. Significant differences in ReHo between the two bands were found in fusiform gyrus and superior frontal gyrus (slow-4> slow-5), and in basal ganglia, parahippocampus, and dorsal middle prefrontal gyrus (slow-5> slow-4). Importantly, we identified significant interaction between frequency bands and groups in the inferior occipital gyrus and caudate body. This study demonstrates that ReHo changes in schizophrenia are widespread and frequency dependent

Task-Switching Performance Improvements After Tai Chi Chuan Training Are Associated With Greater Prefrontal Activation in Older Adults

Studies have shown that Tai Chi Chuan (TCC) training has benefits on task-switching ability. However, the neural correlates underlying the effects of TCC training on task-switching ability remain unclear. Using task-related functional magnetic resonance imaging (fMRI) with a numerical Stroop paradigm, we investigated changes of prefrontal brain activation and behavioral performance during task-switching before and after TCC training and examined the relationships between changes in brain activation and task-switching behavioral performance. Cognitively normal older adults were randomly assigned to either the TCC or control (CON) group. Over a 12-week period, the TCC group received three 60-min sessions of Yang-style TCC training weekly, whereas the CON group only received one telephone consultation biweekly and did not alter their life style. All participants underwent assessments of physical functions and neuropsychological functions of task-switching, and fMRI scans, before and after the intervention. Twenty-six (TCC, N = 16; CON, N = 10) participants completed the entire experimental procedure. We found significant group by time interaction effects on behavioral and brain activation measures. Specifically, the TCC group showed improved physical function, decreased errors on task-switching performance, and increased left superior frontal activation for Switch > Non-switch contrast from pre- to post-intervention, that were not seen in the CON group. Intriguingly, TCC participants with greater prefrontal activation increases in the switch condition from pre- to post-intervention presented greater reductions in task-switching errors. These findings suggest that TCC training could potentially provide benefits to some, although not all, older adults to enhance the function of their prefrontal activations during task-switching

Deterministic diffusion fiber tracking improved by quantitative anisotropy

Diffusion MRI tractography has emerged as a useful and popular tool for mapping connections between brain regions. In this study, we examined the performance of quantitative anisotropy (QA) in facilitating deterministic fiber tracking. Two phantom studies were conducted. The first phantom study examined the susceptibility of fractional anisotropy (FA), generalized factional anisotropy (GFA), and QA to various partial volume effects. The second phantom study examined the spatial resolution of the FA-aided, GFA-aided, and QA-aided tractographies. An in vivo study was conducted to track the arcuate fasciculus, and two neurosurgeons blind to the acquisition and analysis settings were invited to identify false tracks. The performance of QA in assisting fiber tracking was compared with FA, GFA, and anatomical information from T 1-weighted images. Our first phantom study showed that QA is less sensitive to the partial volume effects of crossing fibers and free water, suggesting that it is a robust index. The second phantom study showed that the QA-aided tractography has better resolution than the FA-aided and GFA-aided tractography. Our in vivo study further showed that the QA-aided tractography outperforms the FA-aided, GFA-aided, and anatomy-aided tractographies. In the shell scheme (HARDI), the FA-aided, GFA-aided, and anatomy-aided tractographies have 30.7%, 32.6%, and 24.45% of the false tracks, respectively, while the QA-aided tractography has 16.2%. In the grid scheme (DSI), the FA-aided, GFA-aided, and anatomy-aided tractographies have 12.3%, 9.0%, and 10.93% of the false tracks, respectively, while the QA-aided tractography has 4.43%. The QA-aided deterministic fiber tracking may assist fiber tracking studies and facilitate the advancement of human connectomics. © 2013 Yeh et al

Magnetic resonance imaging of structured-based ventricular mechanics

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1998.Vita.Includes bibliographical references (p. 129-135).The relation between myocardial kinematics and underlying architectural components is the key to understanding the functional design of the ventricular myocardium. This thesis develops a completely noninvasive method, registered diffusion and strain MRI, to acquire information about myocardial architecture and myocardial strain under identical in-vivo conditions. This noninvasive methodology solves important limitations of existing methods all of which require myocardial dissection. It provides metrically correct data of myocardial structure and myocardial function without postmortem distortion. Further, it can be applied to living humans and allows examinations of multiple time horizons, essential to the study of normal development and disease. To provide a valid MR methodology to study myocardial structure and structure-function relations in living humans, we focus on the three steps most essential to achieving this goal: 1) validate the correspondence between diffusion MRI and myocardial architecture, particularly the fiber and sheet organizations; 2) develop a practical method of measuring myocardial diffusion in vivo; 3) show that data obtained by registered diffusion and strain MRI can be employed to address important questions about myocardial structure-function relations. To validate the ability of diffusion MRI to map myocardial architecture, we show, with a novel printing technique, that the deviation of sheet orientations is within MR noise from those in the cow heart specimens. The correspondence between directions of greatest diffusivity and fiber orientations is also verified by the consistency of architectural patterns in MRI of the cadaver heart with those reported in histology. To measure myocardial diffusion in vivo, a robust MR method is developed. In the normal heart that has the synchronous contraction, we show that the strain effect is negligibly small at time points relative to which the mean strain over one cardiac cycle equals zero: "sweet spots." Using this fact, we localize the sweet spots and show that the depicted myocardial fiber architecture agrees with the ex-vivo results. Using registered diffusion and strain MRI, we obtain first quantitative maps of fiber and sheet dynamics in human hearts. Anatomically, MRI shows the classic pattern of fiber helix angles, namely a smooth transmural variation from a left-handed helix at the epicardium to a right-handed helix at the endocardium. It also shows a septum-versus-free-wall polarization of sheet orientations, a pattern recently documented in canine hearts. Analysis of conjoint data of diffusion and strain gives a clear picture of myocardial structure-function relations: 1) systolic fiber shortening, 11±3% relative to end-diastole, is exceptionally uniform across the wall; 2) cross-fiber shortening has a steep transmural slope; it is produced by a linear variation of angles between fibers and directions of principal shortening against wall depth (from 0 at the epicardium to 900 at the endocardium). Moreover, MRI shows two new findings: 1) there is no difference in fiber shortening between trabecular and compact myocardium; 2) sheet orientations are optimized to maximize sheet shear. In conclusion, registered diffusion and strain MRI can map myocardial structure and structure-function relations practically and reliably in living human subjects. The noninvasive and spatially resolved characteristics of this methodology will facilitate investigation of myocardial mechanics in human disease.by Wen-Yih Isaac Tseng.Ph.D

Introduction to Cardiovascular Magnetic Resonance: Technical Principles and Clinical Applications

Cardiovascular magnetic resonance (CMR) is a set of magnetic resonance imaging (MRI) techniques designed to assess cardiovascular morphology, ventricular function, myocardial perfusion, tissue characterization, flow quantification and coronary artery disease. Since MRI is a non-invasive tool and free of radiation, it is suitable for longitudinal monitoring of treatment effect and follow-up of disease progress. Compared to MRI of other body parts, CMR faces specific challenges from cardiac and respiratory motion. Therefore, CMR requires synchronous cardiac and respiratory gating or breath-holding techniques to overcome motion artifacts. This article will review the basic principles of MRI and introduce the CMR techniques that can be optimized for enhanced clinical assessment

Sparse solution of fiber orientation distribution function by diffusion decomposition.

Fiber orientation is the key information in diffusion tractography. Several deconvolution methods have been proposed to obtain fiber orientations by estimating a fiber orientation distribution function (ODF). However, the L 2 regularization used in deconvolution often leads to false fibers that compromise the specificity of the results. To address this problem, we propose a method called diffusion decomposition, which obtains a sparse solution of fiber ODF by decomposing the diffusion ODF obtained from q-ball imaging (QBI), diffusion spectrum imaging (DSI), or generalized q-sampling imaging (GQI). A simulation study, a phantom study, and an in-vivo study were conducted to examine the performance of diffusion decomposition. The simulation study showed that diffusion decomposition was more accurate than both constrained spherical deconvolution and ball-and-sticks model. The phantom study showed that the angular error of diffusion decomposition was significantly lower than those of constrained spherical deconvolution at 30° crossing and ball-and-sticks model at 60° crossing. The in-vivo study showed that diffusion decomposition can be applied to QBI, DSI, or GQI, and the resolved fiber orientations were consistent regardless of the diffusion sampling schemes and diffusion reconstruction methods. The performance of diffusion decomposition was further demonstrated by resolving crossing fibers on a 30-direction QBI dataset and a 40-direction DSI dataset. In conclusion, diffusion decomposition can improve angular resolution and resolve crossing fibers in datasets with low SNR and substantially reduced number of diffusion encoding directions. These advantages may be valuable for human connectome studies and clinical research

The fiber ODFs obtained by applying diffusion deconvolution and diffusion decomposition to QBI, DSI, and GQI.

<p>Each of the methods reconstructs diffusion ODF from shell, grid, and two-shell sampling schemes, respectively. Both diffusion deconvolution and diffusion decomposition can be equally applied to QBI, DSI, and GQI to improve their ability to resolve crossing fibers, but the fiber ODFs obtained from deconvolution shows blunt lobes with fluctuating baseline, whereas those from decomposition show sharp spikes with clean baseline, suggesting that diffusion decomposition can achieve better sensitivity and specificity in resolving crossing fibers.</p

Fiber volume mapping versus FA mapping.

<p>(A) The mapping of the total fiber volume calculated from diffusion decomposition and (B) the mapping of the fractional anisotropy (FA) calculated from the diffusion tensor analysis applied to the same data. The FA mapping shows decreased values in the centrum semiovale due to the crossing fibers in this region (annotated), whereas the total fiber volume mapping shows a relatively homogeneous intensity throughout the white matter. This suggests that the fiber volume can provide a better gray-white matter separation and facilitate further investigation into structural integrity.</p