Double-Sampled Echo-Planar Imaging at 3 Tesla

Yang, Qing; Posse, Stefan; Bihan, Denis Le; Smith, Michael B.

doi:10.1006/jmrb.1996.0167

Cited by 28 publications

(35 citation statements)

References 3 publications

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“…A 3D EPI scan was used to obtain isotropic high-resolution images with high SNR. To avoid EPI ghosting artifacts, even and odd echoes were separately reconstructed into magnitude images before the two sets of images were averaged together (61). Echo time was reduced by acquiring the EPI train in 16 segments.…”

Section: Methodsmentioning

confidence: 99%

Anatomical accuracy of brain connections derived from diffusion MRI tractography is inherently limited

Thomas

İrfanoğlu

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

701

633

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Tractography based on diffusion-weighted MRI (DWI) is widely used for mapping the structural connections of the human brain. Its accuracy is known to be limited by technical factors affecting in vivo data acquisition, such as noise, artifacts, and data undersampling resulting from scan time constraints. It generally is assumed that improvements in data quality and implementation of sophisticated tractography methods will lead to increasingly accurate maps of human anatomical connections. However, assessing the anatomical accuracy of DWI tractography is difficult because of the lack of independent knowledge of the true anatomical connections in humans. Here we investigate the future prospects of DWI-based connectional imaging by applying advanced tractography methods to an ex vivo DWI dataset of the macaque brain. The results of different tractography methods were compared with maps of known axonal projections from previous tracer studies in the macaque. Despite the exceptional quality of the DWI data, none of the methods demonstrated high anatomical accuracy. The methods that showed the highest sensitivity showed the lowest specificity, and vice versa. Additionally, anatomical accuracy was highly dependent upon parameters of the tractography algorithm, with different optimal values for mapping different pathways. These results suggest that there is an inherent limitation in determining long-range anatomical projections based on voxelaveraged estimates of local fiber orientation obtained from DWI data that is unlikely to be overcome by improvements in data acquisition and analysis alone.T he creation of a comprehensive map of the connectional neuroanatomy of the human brain would be a fundamental achievement in neuroscience. However, despite the numerous efforts to date (for a historical review, see ref. 1), creating this map remains a challenge. A major limitation is that the current goldstandard technique for mapping structural connections, which requires the injection of axonal tracers, cannot be used in humans. The introduction of diffusion-weighted MRI (DWI) (2-4) and the subsequent advent of diffusion tensor MRI (DTI) (5) opened the possibility of exploring the structural properties of white matter in the living human brain (6). Local DWI measures are used clinically for the early detection of stroke and for the characterization of neurological disorders such as multiple sclerosis, epilepsy, and brain gliomas, among others (7). In addition, tractography approaches (8-12) that can infer structural brain connectivity based on brain-wide local DWI measurement have been developed (for reviews, see refs. 13 and 14). The success of DWI tractography as a method for studying fiber trajectories has led to a systematic characterization of large white-matter pathways of the living human brain (e.g., ref. 15), and now it is used routinely to provide a structural explanation for aspects of human brain function (16).A major limitation of DWI tractography is that its characterization of axonal pathways is based on indirec...

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Section: Methodsmentioning

confidence: 99%

Anatomical accuracy of brain connections derived from diffusion MRI tractography is inherently limited

Thomas

İrfanoğlu

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

701

633

View full text Add to dashboard Cite

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“…A double-sampled EPI readout (Yang et al, 1996), which samples the same k-space line twice, with both positive and negative gradients, was incorporated into the GRASE sequence to enhance SNR, as well as to reduce artifacts from imperfect read-out gradients. A twin-navigator (Mori and van Zijl, 1998) was implemented to correct motion-induced phase errors, and no respiration trigger was used.…”

Section: Methodsmentioning

confidence: 99%

Localized diffusion magnetic resonance micro-imaging of the live mouse brain

Reisinger

et al. 2014

NeuroImage

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High-resolution diffusion MRI (dMRI) is useful for resolving complex microstructures in the mouse brain, but technically challenging for in vivo studies due to the long scan time. In this study, selective excitation and a three-dimensional fast imaging sequence were used to achieve in vivo high-resolution dMRI of the mouse brain at 11.7 Tesla. By reducing the field of view using spatially selective radio frequency pulses, we were able to focus on targeted brain structures and acquire high angular resolution diffusion imaging (HARDI) data at an isotropic resolution of 0.1 mm and 30 diffusion encoding directions in approximately one hour. We investigated the complex tissue microstructures of the mouse hippocampus, cerebellum, and several cortical areas using this localized dMRI approach, and compared the results with histological sections stained with several axonal and dendritic markers. In the mouse visual cortex, the results showed predominately radially arranged structures in an outer layer and tangentially arranged structures in an inner layer, similar to observations from postmortem human brain specimens.

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“…Nyquist ghosts are an inherent artifact in EPI, and there are many approaches to correct them including double-sampled (DS) EPI [4], the 1D phase-correction approach of Ahn and Cho (AC) [5], 2D phase-mapping [6], and phase labeling (PLACE) [7]. Although DS-EPI completely eliminates Nyquist ghosts it has the disadvantage of doubling the echo train length, which leads to greater susceptibility artifact distortion.…”

Section: Theorymentioning

confidence: 99%

Improved PASL EPI acquisitions with parallel imaging and unfold

Hoge

Tan

Kraft

2008

2008 42nd Asilomar Conference on Signals, Systems and Computers

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Pulsed Arterial Spin Labeling (PASL) has been shown to be an effective method for quantitatively measuring cerebral blood flow. Quantification errors with PASL may result from patient motion, however, so Echo Planar Imaging (EPI) is commonly used to acquire PASL images due to its high temporal resolution. EPI achieves high temporal resolution through long echo trains, which can result in image distortions due to magnetic field inhomogeneities. Thus, perfusion weighted EPI could be further improved with shorter echo trains and faster image acquisitions. This paper investigates the use of UNFOLD and parallel MR imaging to reduce EPI image acquisition time. We demonstrate how the use of varied sampling patterns and UNFOLD can completely remove the 'Nyquist ghosts' that are common in EPI acquisitions. This allows one to greatly improve the effectiveness of parallel imaging in EPI, and to reduce field inhomogeneity artifacts by reducing the echo train length.

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Double-Sampled Echo-Planar Imaging at 3 Tesla

Cited by 28 publications

References 3 publications

Anatomical accuracy of brain connections derived from diffusion MRI tractography is inherently limited

Anatomical accuracy of brain connections derived from diffusion MRI tractography is inherently limited

Localized diffusion magnetic resonance micro-imaging of the live mouse brain

Improved PASL EPI acquisitions with parallel imaging and unfold

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