Characterization of U-shape streamline fibers: Methods and applications

Diffusion tensor imaging (DTI), high angular resolution diffusion imaging (HARDI), and Diffusion Spectrum Imaging (DSI) have been widely used in the neuroimaging field to examine the macro-scale fiber connection patterns in the cerebral cortex. However, the topographic and geometric relationships between diffusion imaging derived streamline fiber connection patterns and cortical folding patterns remain largely unknown. This paper specifically identifies and characterizes the U-shapes of diffusion imaging derived streamline fibers via a novel fiber clustering framework and examines their co-localization patterns with cortical sulci based on DTI, HARDI, and DSI datasets of human, chimpanzee and macaque brains. We verified the presence of these U-shaped streamline fibers that connect neighboring gyri by coursing around cortical sulci such as the central sulcus, pre-central sulcus, post-central sulcus, superior temporal sulcus, inferior frontal sulcus, and intra-parietal sulcus. This study also verified the existence of U-shape fibers across data modalities (DTI/HARDI/DSI) and primate species (macaque, chimpanzee and human), and suggests that the common pattern of U-shape fibers coursing around sulci is evolutionarily-preserved in cortical architectures

Axonal Fiber Terminations Concentrate on Gyri

Convoluted cortical folding and neuronal wiring are 2 prominent attributes of the mammalian brain. However, the macroscale intrinsic relationship between these 2 general cross-species attributes, as well as the underlying principles that sculpt the architecture of the cerebral cortex, remains unclear. Here, we show that the axonal fibers connected to gyri are significantly denser than those connected to sulci. In human, chimpanzee, and macaque brains, a dominant fraction of axonal fibers were found to be connected to the gyri. This finding has been replicated in a range of mammalian brains via diffusion tensor imaging and high–angular resolution diffusion imaging. These results may have shed some lights on fundamental mechanisms for development and organization of the cerebral cortex, suggesting that axonal pushing is a mechanism of cortical folding

Genetic mapping and evolutionary analysis of human-expanded cognitive networks

Cognitive brain networks such as the default-mode network (DMN), frontoparietal network, and salience network, are key functional networks of the human brain. Here we show that the rapid evolutionary cortical expansion of cognitive networks in the human brain, and most pronounced the DMN, runs parallel with high expression of human-accelerated genes (HAR genes). Using comparative transcriptomics analysis, we present that HAR genes are differentially more expressed in higher-order cognitive networks in humans compared to chimpanzees and macaques and that genes with high expression in the DMN are involved in synapse and dendrite formation. Moreover, HAR and DMN genes show significant associations with individual variations in DMN functional activity, intelligence, sociability, and mental conditions such as schizophrenia and autism. Our results suggest that the expansion of higher-order functional networks subserving increasing cognitive properties has been an important locus of genetic changes in recent human brain evolution

Chimpanzee (Pan troglodytes) Precentral Corticospinal System Asymmetry and Handedness: A Diffusion Magnetic Resonance Imaging Study

Most humans are right handed, and most humans exhibit left-right asymmetries of the precentral corticospinal system. Recent studies indicate that chimpanzees also show a population-level right-handed bias, although it is less strong than in humans.We used in vivo diffusion-weighted and T1-weighted magnetic resonance imaging (MRI) to study the relationship between the corticospinal tract (CST) and handedness in 36 adult female chimpanzees. Chimpanzees exhibited a hemispheric bias in fractional anisotropy (FA, left>right) and mean diffusivity (MD, right>left) of the CST, and the left CST was centered more posteriorly than the right. Handedness correlated with central sulcus depth, but not with FA or MD.These anatomical results are qualitatively similar to those reported in humans, despite the differences in handedness. The existence of a left>right FA, right>left MD bias in the corticospinal tract that does not correlate with handedness, a result also reported in some human studies, suggests that at least some of the structural asymmetries of the corticospinal system are not exclusively related to laterality of hand preference

Numerical simulation of in vitro pulsatile flow and its study using FRISK, a rapid phase contrast technique

Purpose: To test the potential of a phase contrast magnetic resonance (PC-MR) sparse sampling technique, fragmented regional interpolation segmentation for k-space (FRISK), to capture complex flow features within a breathhold duration by using numerical simulations and experimental approaches. Materials and Methods: Computational fluid dynamics (CFD) data of three models were generated: a two-chamber orifice flow model simulating valvular regurgitation, a femoral artery model, and a U-shaped model simulating the aortic arch. These data were used to simulate conventional and FRISK PC-MR data acquisitions. FRISK parameters can be adapted for different flow fields to capture either high temporal information or complexly varying spatial information with a temporal component or a mixture of both. In vivo PC-MR images on a healthy volunteer were sampled to compare conventional PC-MR with novel FRISK imaging. Results: In our simulations of three representative models, when only the errors from different sampling sequences were considered, FRISK was shown to maintain or even improve data accuracy while cutting the scan time by at least 50% compared to corresponding conventional PC-MR. By adapting the FRISK parameters for flowfields with different features, FRISK was capable of capturing in-plane and through-plane velocity information with excellent detail in approximately 20 heartbeats breathhold duration. The results of the in vivo MR experiment were consistent with the simulation results, showing that breathhold FRISK imaging improved spatial resolution of the data and maintained adequate temporal resolution compared with breathhold conventional imaging. Conclusion: FRISK, a new MRI sampling sequence that sparsely samples data and aligns acquired data during postprocessing, provides a scan time advantage of approximately a factor of 2 compared to conventional scans, and allowed rapid or breathhold scanning while obtaining acceptable accuracy

Numerical and experimental study of a novel phase contrast magnetic resonance (PC-MR) imaging technique: Sparse Interleaved Referencing PC-MR imaging

Purpose: To use numerical simulation and experimental approaches to introduce a novel phase contrast magnetic resonance (PC-MR) data processing technique termed Sparse Interleaved Referencing PC-MR, with potential to improve accuracy, temporal resolution, and signal-to-noise ratio (SNR) of PC-MR data. Materials and Methods: Computational fluid dynamics data were generated for a two-chamber orifice flow model simulating valvular regurgitation. The numerical results were validated and used to simulate conventional and Sparse Interleaved Referencing PC-MR data acquisitions. Common data sets were processed using conventional and Sparse Interleaved Referencing approaches and quantitative errors in velocity-time waveforms were measured and compared. In vitro phantom jet flow data and in vivo ascending aorta data were acquired and used to simulate Sparse Interleaved Referencing PC-MR. Results: The Sparse Interleaved Referencing PC-MR data showed significantly better representation of the velocity-time waveform in three areas: (i) lower root-mean-square errors (9.0 ± 1.0% versus 24.0 ± 0.2%; P < 0.005), (ii) simulation of conventionally processed data showed a pattern of peak velocity overestimation, which was experimentally demonstrated in in vitro data, whereas overestimation of peak velocity was dramatically attenuated using Sparse Interleaved Referencing (2.8 ± 0.4% versus 16.9 ± 6.4%, P < 0.005), and (iii) compared with the conventional scan, an average of 119.4 ± 26.6% (P < 0.005) SNR was realized in in vitro and in vivo Sparse Interleaved Referencing PC-MR data. Conclusion: Simulation and in vitro/in vivo results show that Sparse Interleaved Referencing PC-MR processed data in pulsatile and jet flow showed higher accuracy, better peak velocity representation, and improved SNR compared with the data processed using the conventional PC-MR method

A spheroidal control volume for the quantitative measurement of regurgitant flow by cardiac MRI

Purpose: We sought to show that a spheroidally shaped control volume (CV), formed from a minimal MRI data set, can be used to measure regurgitant flow through a defective cardiac valve consistently and accurately under a variety of flow conditions. Materials and Methods: Using a pulsatile flow pump and phantoms simulating severe valvular regurgitation, we acquired 31 scans of two or three radially oriented slices, using a variety of flow waveforms and regurgitant volumes of 12 to 55 ml. Data sets included high- and low-resolution scans, and variable-rate sparse sampling was also applied to reduce the scan time. An oblate spheroid was placed in the pump chamber opposite the jet and fit as tightly as possible to isomagnitude velocity contours at 25% of the velocity encoding limit. Results: Normalized regurgitant volumes (NRVs) expressed as a percentage of the pump setting were obtained from the product of the spheroid surface area with the velocities normal to it. Mean ± SD NRV values were 96.8 ± 6.6% for all scans. Imaging times in the breath-hold range were obtained using reduced resolution and variable-rate sparse sampling approaches without significant degradation in accuracy. Conclusion: In our preliminary findings, the spheroidal CV method showed clear potential for the development of a robust, clinically feasible technique for the measurement of regurgitant volume

Self-adaptive rolling motion for snake robots in unstructured environments based on torque control

Snake robots have great potential for exploring and operating in challenging unstructured environments, such as rubble, caves, and narrow pipelines. However, due to the complexity and unpredictability of unstructured environments, designing a controller that can achieve adaptive motion is crucial. This paper proposes a self-adaptive torque-based rolling controller for snake robots, enabling compliant motion in unstructured environments. First, a controller is designed to modify the torque of each motor by focusing on the different motion states of the rolling gait. Second, an experimental platform is established for snake robots to verify the effectiveness of the controller. Finally, a series of rolling experiments are conducted using the torque-based rolling controller. In conclusion, the self-adaptive torque-based rolling controller enhances snake robot adaptability and mobility