Yung-Chin Hsu

A large deformation diffeomorphic metric mapping solution for diffusion spectrum imaging datasets

Spatial transformation for diffusion spectrum imaging (DSI) is an important step for group analyses of DSI datasets. In this study, we developed a transformation method for DSI datasets under the framework of large deformation diffeomorphic metric mapping (LDDMM), which is termed LDDMM-DSI. The proposed method made use of the fact that a DSI dataset is 6D, and generalized the original 2D/3D LDDMM algorithm to the 6D case with some modifications made for the DSI datasets. In this manner, the conventional reorientation problem that arises from transforming diffusion-weighted datasets was avoided by making the DSI datasets capable of being freely deformed in the q-space. The algorithm treated the data-matching task as a variational problem under the LDDMM framework and sought optimal velocity fields from which the generated transformations were diffeomorphic and the transformation curve was a geodesic. The mathematical materials and numerical implementation are detailed in the paper, and experiments were performed to analyze the proposed method on real brain DSI datasets. The results showed that the method was capable of registering different DSI datasets in both global structural shapes and local diffusion profiles. In conclusion, the proposed method can facilitate group analyses of DSI datasets and the generation of a DSI template.

Correction for Susceptibility-Induced Distortion in Echo-Planar Imaging Using Field Maps and Model-Based Point Spread Function

Susceptibility-induced distortion is one of the major artifacts in echo-planar imaging (EPI), and many solutions have been proposed for the problem, including the Fourier method and the point spread function (PSF) method. In this paper, a framework unifying both methods is presented. Under this framework, a model-based PSF method is proposed in which the PSF of the source object is modeled along with a single field map measured by TE-offset reference scans. EPI images of a phantom and a healthy human subject were acquired, and the results of distortion correction by the Fourier method, linear interpolation method, and the model-based PSF method were compared. The results showed that the model-based PSF method could correct for geometric distortion and signal intensity distortion satisfactorily, avoiding the rippling artifact shown in the Fourier method. In conclusion, the proposed framework gave us an overall picture of how different correction methods work. The model-based PSF method, which required fewer reference scans and less computational load, was more clinically feasible than other methods.

Primary and secondary alterations of white matter connectivity in schizophrenia: A study on first-episode and chronic patients using whole-brain tractography-based analysis.

Schizophrenia is a debilitating mental disorder that is associated with an impaired connection of cerebral white matter. Studies on patients with chronic and first-episode schizophrenia have found widespread white matter abnormalities. However, it is unclear whether the altered connections are inherent in or secondary to the disease. Here, we sought to identify white matter tracts with altered connections and to distinguish primary or secondary alterations among 74 fiber tracts across the whole brain using an automatic tractography-based analysis method. Thirty-one chronic, 25 first-episode patients with schizophrenia and 31 healthy controls were recruited to receive diffusion spectrum magnetic resonance imaging at 3T. Seven tracts were found to exhibit significant differences between the groups; they included the right arcuate fasciculus, bilateral fornices, left superior longitudinal fasciculus I, and fibers of the corpus callosum to the bilateral dorsolateral prefrontal cortices (DLPFC), bilateral temporal poles, and bilateral hippocampi. Post-hoc between-group analyses revealed that the connection of the callosal fibers to the bilateral DLPFC was significantly decreased in chronic patients but not in first-episode patients. In a stepwise regression analysis, the decline of the tract connection was significantly predicted by the duration of illness. In contrast, the remaining six tracts showed significant alterations in both first-episode and chronic patients and did not associate with clinical variables. In conclusion, reduced white matter connectivity of the callosal fibers to the bilateral DLPFC may be a secondary change that degrades progressively in the chronic stage, whereas alterations in the other six tracts may be inherent in the disease.

Reduced structural integrity and functional lateralization of the dorsal language pathway correlate with hallucinations in schizophrenia: a combined diffusion spectrum imaging and functional magnetic resonance imaging study.

Recent studies suggest that structural and functional alterations of the language network are associated with auditory verbal hallucinations (AVHs) in schizophrenia. However, the ways in which the underlying structure and function of the network are altered and how these alterations are related to each other remain unclear. To elucidate this, we used diffusion spectrum imaging (DSI) to reconstruct the dorsal and ventral pathways and employed functional magnetic resonance imaging (fMRI) in a semantic task to obtain information about the functional activation in the corresponding regions in 18 patients with schizophrenia and 18 matched controls. The results demonstrated decreased structural integrity in the left ventral, right ventral and right dorsal tracts, and decreased functional lateralization of the dorsal pathway in schizophrenia. There was a positive correlation between the microstructural integrity of the right dorsal pathway and the functional lateralization of the dorsal pathway in patients with schizophrenia. Additionally, both functional lateralization of the dorsal pathway and microstructural integrity of the right dorsal pathway were negatively correlated with the scores of the delusion/hallucination symptom dimension. Our results suggest that impaired structural integrity of the right dorsal pathway is related to the reduction of functional lateralization of the dorsal pathway, and these alterations may aggravate AVHs in schizophrenia.

Shared and distinct alterations of white matter tracts in remitted and nonremitted patients with schizophrenia

Patients with schizophrenia do not usually achieve remission state even after adequate antipsychotics treatment. Previous studies found significant difference in white matter integrity between patients with good outcomes and those with poor outcomes, but difference is still unclear at individual tract level. This study aimed to use a systematic approach to identify the tracts that were associated with remission state in patients with schizophrenia. We evaluated 91 patients with schizophrenia (remitted, 50; nonremitted, 41) and 50 healthy controls through diffusion spectrum imaging. White matter tract integrity was assessed through an automatic tract‐specific analysis method to determine the mean generalized fractional anisotropy (GFA) values of the 76 white matter tract bundles in each participant. Analysis of covariance among the 3 groups revealed 12 tracts that were significantly different in GFA values. Post‐hoc analysis showed that compared with the healthy controls, the nonremission group had reduced integrity in all 12 tracts, whereas the remission group had reduced integrity in only 4 tracts. Comparison between the remission and nonremission groups revealed 4 tracts with significant difference (i.e., the right fornix, bilateral uncinate fasciculi, and callosal fibers connecting the temporal poles) even after adjusting age, sex, education year, illness duration, and medication dose. Furthermore, all the 4 tracts were correlated with negative symptoms scores of the positive and negative syndrome scale. In conclusion, our study identified the tracts that were associated with remission state of schizophrenia. These tracts might be a potential prognostic marker for the symptomatic remission in patients with schizophrenia.

Altered white-matter integrity in unaffected siblings of probands with autism spectrum disorders: White-Matter Integrity in Unaffected Siblings of ASD

Despite the evidence of altered white‐matter tract property in individuals with autism spectrum disorder (ASD), little is known about their unaffected siblings. This study aimed to investigate white‐matter integrity in unaffected siblings of ASD probands. Thirty‐nine unaffected siblings (mean age 15.6 ± 6.0 years; 27 males, 69.2%) and 39 typically developing controls (TDC) (14.2 ± 5.6 years; 26 males, 66.7%) were assessed with diffusion spectrum images and neuropsychological tests. Using the tract‐based automatic analysis and the threshold‐free cluster weighted (TFCW) scores, we searched for the segments among 76 tracts with the largest difference over the entire brain compared to TDC. Tract integrity was quantified by calculating the mean generalized fractional anisotropy (mGFA) values of the segments with the largest difference in TFCW scores. Unaffected siblings showed reduced mGFA in the bilateral frontal aslant tracts, the right superior longitudinal fasciculus 2 (SLF2), the frontostriatal tracts from the right dorsolateral and left ventrolateral prefrontal cortices, the thalamic radiations of the left ventral and the right dorsal thalamus, the callosal fibers of the splenium, and the increased mGFA of the callosal fibers of the precuneus and the left inferior longitudinal fasciculus. Among these, reduced right SLF2 mGFA was associated with social awareness deficits; impaired frontostriatal tract was associated with internalizing problems, while right frontal aslant tract integrity was associated with visual memory deficits. In conclusion, unaffected siblings showed the aberrant integrity of several white‐matter tracts, which were correlated with clinical symptoms and neurocognitive dysfunction. The altered tract integrity could be further examined in the probands with ASD. Hum Brain Mapp 38:6053–6067, 2017.

The acceleration of pipeline workloads under the FPGA area and bandwidth constraints

This work is motivated by the advance of heterogeneous computing and the strong demands of workload acceleration in practice. By considering pipeline workloads over FPGA, this paper explores a systematic methodology to configure the hardware instances of each pipeline stage such that the maximum of the execution time of each stage is minimized, where the FPGA allocation with the memory bandwidth constraint is considered. For the target problem, an algorithm is proposed and proved being optimal, and a real implementation study is conducted. In the experimental results, an image filter FPGA implementation can outperform the CPU, GPU, and baseline FPGA solutions by 460%, 73%, and 1030%, respectively. Extensive simulations were also conducted with a large FPGA size to show the scalability of this work.

T182. SHARED AND DISTINCT ALTERATIONS IN THE WHITE MATTER TRACTS OF REMITTED AND NON-REMITTED PATIENTS WITH SCHIZOPHRENIA

Abstract Background Antipsychotic drugs are the standard treatment for schizophrenia; however, the treatment outcomes vary. Different treatment outcomes may be attributed to the genetic and molecular heterogeneity of patients, which may be represented in the white matter structures of the brain. In the present study, we assessed the association between white matter tract integrity and treatment outcomes in patients with schizophrenia. Methods We evaluated 96 patients with schizophrenia (remitted, 53; non-remitted, 43) and 50 healthy controls through diffusion spectrum imaging with a 3 Tesla magnetic resonance imaging scanner. Patients were categorized into the remission and non-remission groups according to the criteria proposed by The Remission in Schizophrenia Working Group (RSWG) on the basis of PANSS scores. White matter tract integrity was assessed through an automatic tract-specific analysis method to determine the mean generalized fractional anisotropy (GFA) values of the 76 white matter tract bundles in each participant. Results Analysis of covariance revealed that 7 tracts, namely the bilateral fornices, the bilateral uncinate fasciculi, and the callosal fibers (CFs) of the bilateral temporal poles, bilateral hippocampi, and bilateral amygdalae, had significantly different GFA values among the 3 groups. Posthoc between-groups analysis showed that the non-remission group had lower GFA values in all 7 tracts than the control group; the remission group had lower GFA values than the control group only in 4 tracts, namely the bilateral fornices and the CFs of the bilateral temporal poles, and bilateral hippocampi. Compared with the remission group, the non-remission group had lower GFA values in all 7 tracts. Discussion All 7 tracts that were altered in the non-remission group are a part of the limbic system, which supports various functions, including emotions, memory, and learning. Our results suggest that patients who had poor outcomes to antipsychotic treatments might have more severe disruptions in the limbic system. The 7 altered tracts in the non-remission group are compatible with those reported in previous studies on white matter or gray matter alterations. In a cross-sectional tractography-based study on 3 pairs of association fibers (i.e., the cingulum, superior longitudinal fasciculus, and uncinate fasciculus), Luck et al reported that compared with patients with good outcomes, patients with poor outcomes had reduced FA in the uncinate fasciculus and superior longitudinal fasciculus. Marques et al performed a longitudinal study using tract-based spatial statistics and reported that non-responders had more tracts with a significantly lower FA than did the responders, particularly in the uncinate fasciculus and corpus callosum. In addition to the uncinate fasciculus, we also observed reduced fiber integrity in the bilateral fornices and the CFs of the bilateral temporal poles, bilateral hippocampi, and bilateral amygdalae; these tracts connect the gray matter in the limbic system. Jääskeläinen et al revealed that a reduction in gray matter volume in the frontal and limbic areas is associated with overall poor outcomes. In addition, Van Haren et al reported significantly reduced gray matter volumes in the frontal and temporal cortices of the individuals with poor outcomes. Because the gray matter regions are anatomically connected by the fiber tracts, gray matter reduction in the limbic system might affect the interconnecting fiber tracts; this finding accords with the findings of the present study. In conclusion, differences in the severity of white matter tract alterations in the remission and non-remission groups might indicate biologically distinct subgroups in schizophrenia.

Impaired Callosal Motor Fiber Integrity and Upper Extremity Motor Impairment Are Associated With Stroke Lesion Location

Background. Damage to the callosal motor fibers (CMFs) may affect motor recovery in patients with stroke. However, whether the severity of CMF impairment varies with lesion locations remains unclear. Objective. To investigate (1) whether CMF impairment occurs after stroke and whether the impairment varies with lesion locations and (2) the associations of CMF impairment and upper extremity (UE) motor impairment. Methods. Twenty-nine patients with lesions involving the corticospinal tract (CST) were categorized into 2 groups: lesions involving the CMFs (CMF group, n = 15), and lesions not involving the CMFs (non-CMF group, n = 14). Thirteen healthy adults served as the control group. Tract integrity, assessed by the mean generalized fractional anisotropy (mGFA) using diffusion spectrum imaging, of the CMFs and the CST above the internal capsule (CSTABOVE) of the ipsilesional hemisphere were compared. Results. After accounting for the effect of lesion load on the CST, the CMF group exhibited a significantly lower mGFA of the CMFs than did the control and non-CMF groups (post hoc P = .005 and .001, respectively). No significant difference was observed between the non-CMF and control groups (post hoc P = .999). The CST and CMF impairment accounted for 56% of the variance of UE motor impairment in the CMF group (P = .007), whereas no significant association was observed in the non-CMF group (P = .570). Conclusions. CMF impairment after stroke depends on lesion locations and CMF integrity has an incremental contribution to the severity of UE motor impairment in the CMF group.

Diminution of context association memory structure in subjects with subjective cognitive decline

Alzheimers disease (AD) progresses insidiously from the preclinical stage to dementia. While people with subjective cognitive decline (SCD) have normal cognitive performance, some may be in the preclinical stage of AD. Neurofibrillary tangles appear first in the transentorhinal cortex, followed by the entorhinal cortex in the clinically silent stage of AD. We expected the earliest changes in subjects with SCD to occur in medial temporal subfields other than the hippocampal proper. These selective structural changes would affect specific memory subcomponents. We used the Family Picture subtest of the Wechsler Memory Scale‐III, which was modified to separately compute character, activity, and location subscores for episodic memory subcomponents. We recruited 43 subjects with SCD, 44 subjects with amnesic mild cognitive impairment, and 34 normal controls. MRI was used to assess cortical thickness, subcortical gray matter volume, and fractional anisotropy. The results demonstrated that SCD subjects showed significant cortical atrophy in their bilateral parahippocampus and perirhinal and the left entorhinal cortices but not in their hippocampal regions. SCD subjects also exhibited significantly decreased mean fractional anisotropy in their bilateral uncinate fasciculi. The diminution of cortical thickness over the mesial temporal subfields corresponded to brain areas with early tangle deposition, and early degradation of the uncinate fasciculus was in accordance with the retrogenesis hypothesis. The parahippocampus and perirhinal cortex contribute mainly to context association memory while the entorhinal cortex, along with the uncinate fasciculus, contributes to content‐related contextual memory. We proposed that context association and related memory structures are vulnerable in the SCD stage.