Three-dimensional echo-shifted EPI with simultaneous blip-up and blip-down acquisitions for correcting geometric distortion

Purpose: Echo-planar imaging (EPI) with blip-up/down acquisition (BUDA) can provide high-quality images with minimal distortions by using two readout trains with opposing phase-encoding gradients. Because of the need for two separate acquisitions, BUDA doubles the scan time and degrades the temporal resolution when compared to single-shot EPI, presenting a major challenge for many applications, particularly functional MRI (fMRI). This study aims at overcoming this challenge by developing an echo-shifted EPI BUDA (esEPI-BUDA) technique to acquire both blip-up and blip-down datasets in a single shot. Methods: A three-dimensional (3D) esEPI-BUDA pulse sequence was designed by using an echo-shifting strategy to produce two EPI readout trains. These readout trains produced a pair of k-space datasets whose k-space trajectories were interleaved with opposite phase-encoding gradient directions. The two k-space datasets were separately reconstructed using a 3D SENSE algorithm, from which time-resolved B0-field maps were derived using TOPUP in FSL and then input into a forward model of joint parallel imaging reconstruction to correct for geometric distortion. In addition, Hankel structured low-rank constraint was incorporated into the reconstruction framework to improve image quality by mitigating the phase errors between the two interleaved k-space datasets. Results: The 3D esEPI-BUDA technique was demonstrated in a phantom and an fMRI study on healthy human subjects. Geometric distortions were effectively corrected in both phantom and human brain images. In the fMRI study, the visual activation volumes and their BOLD responses were comparable to those from conventional 3D echo-planar images. Conclusion: The improved imaging efficiency and dynamic distortion correction capability afforded by 3D esEPI-BUDA are expected to benefit many EPI applications.Comment: 8 figures, peer-reviewed journal pape

Finishing the euchromatic sequence of the human genome

The sequence of the human genome encodes the genetic instructions for human physiology, as well as rich information about human evolution. In 2001, the International Human Genome Sequencing Consortium reported a draft sequence of the euchromatic portion of the human genome. Since then, the international collaboration has worked to convert this draft into a genome sequence with high accuracy and nearly complete coverage. Here, we report the result of this finishing process. The current genome sequence (Build 35) contains 2.85 billion nucleotides interrupted by only 341 gaps. It covers ∼99% of the euchromatic genome and is accurate to an error rate of ∼1 event per 100,000 bases. Many of the remaining euchromatic gaps are associated with segmental duplications and will require focused work with new methods. The near-complete sequence, the first for a vertebrate, greatly improves the precision of biological analyses of the human genome including studies of gene number, birth and death. Notably, the human enome seems to encode only 20,000-25,000 protein-coding genes. The genome sequence reported here should serve as a firm foundation for biomedical research in the decades ahead

26th Annual Computational Neuroscience Meeting (CNS*2017): Part 3 - Meeting Abstracts - Antwerp, Belgium. 15–20 July 2017

This work was produced as part of the activities of FAPESP Research,\ud Disseminations and Innovation Center for Neuromathematics (grant\ud 2013/07699-0, S. Paulo Research Foundation). NLK is supported by a\ud FAPESP postdoctoral fellowship (grant 2016/03855-5). ACR is partially\ud supported by a CNPq fellowship (grant 306251/2014-0)

Spatial and Temporal Characteristics of Diffusion MRI: New Developments and Applications

Diffusion processes in biological tissues involve intricate spatial and temporal dynamics modulated by the heterogeneous microstructures. In magnetic resonance imaging (MRI), diffusion-weighted gradients induce signal attenuation, typically analyzed via the Gaussian mono-exponential model. However, this model oversimplifies the diffusion process in biological tissues with complex morphology and spatial heterogeneity. Therefore, advanced non-Gaussian models are essential for more precise tissue characterization. In addition to the spatial characteristics, there's a growing acknowledgment of the temporal dependency in non-Gaussian diffusion models. Studies typically use oscillating-gradient spin-echo (OGSE) or pulsed-gradient stimulated-echo (PGSTE) sequence to shorten or prolong diffusion times. However, the time dependency across a broad range of diffusion time and the consistency in the parameters obtained from different sequences have not been well studied. Additionally, practical limitations in investigating diffusion time dependency lies in the acquisition time, necessitating the development of rapid acquisition techniques that enable multiple diffusion times in a single sequence to ensure efficiency, patient compliance, and data reliability while mitigating motion-induced image misregistration. In this dissertation, both spatial and temporal characteristics of diffusion MRI have been investigated to enable a number of challenging clinical and technical applications. Specifically, an advanced fractional order calculus (FROC) model which recognizes spatial heterogeneity was used to provide a new approach to differentiate insignificant and significant prostate cancer. Diffusion temporal dependency in Sephadex gels with varying bead size and permeability were investigated over a wide diffusion times range using multiple sequences. Finally, a novel time-efficient diffusion MRI acquisition technique was proposed to accelerate time dependent diffusion MRI acquisition

Focused-Ion-Beam Assisted Fabrication Of Individual Multiwall Carbon Nanotube Field Emitter

We report the fabrication of an individual carbon nanotube (CNT) electron field emitter using a focused-ion-beam (FIB) technique. The monolithic multiwall CNT with a graphitic shield is synthesized using chemical vapor deposition technique. The FIB technique is applied to attach the monolithic multiwall CNT on an etched tungsten tip. Field emission measurements are carried out in a vacuum of 10-7 Torr. Threshold voltage as low as 120 V has been obtained. © 2005 Elsevier Ltd. All rights reserved

Synthesis Of Carbon Nanotubes By Electrochemical Deposition At Room Temperature

An electrochemical deposition technique developed for the production of carbon nanotubes from organic solvent at room temperature was investigated. The depositions were carried out at room temperature and magnetic stirring was employed to achieve a uniform distribution of carbonaceous deposit on the cathode. The formation and growth of carbon nanotubes were simulated by the transition metal catalysts. It was found that the electrochemical deposition conditions have a strong influence on the growth morphology of carbon nanotubes. SEM characterization showed that the diameter of carbon nanotubes was of the order of 100 nm and the length of nanotubes can be up to 20 μm

Integrated bioprocess for high-efficiency production of succinic acid in an expanded-bed adsorption system

An integrated fermentation process for the production of succinic acid by Actinobacillus succinogenes at high titer, yield and productivity was developed by applying in situ product removal (ISPR) strategy. The ISPR process was conducted by a coupled expanded-bed adsorption (EBA) system. The novel approach during the product inhibitory period of microbial fermentation enhanced the cell growth of A. succinogenes from 48 h to 126 h, and significantly increased succinic acid production up to the final titer of 145.2 g l(-1) with an average yield of 0.52 g g(-1), and productivity of 1.3 g l(-1) h(-1). The maximum yield and productivity reached 0.76 g g(-1) and 2.58 gl(-1) h(-1), respectively after the first ISPR operation cycle. ISPR process with EBA leads to the production of succinct acid via fermentation economically feasible. (C) 2011 Elsevier B.V. All rights reserved