scispace - formally typeset
Search or ask a question
Author

Lawrence L. Wald

Bio: Lawrence L. Wald is an academic researcher from Harvard University. The author has contributed to research in topics: Electromagnetic coil & Iterative reconstruction. The author has an hindex of 81, co-authored 442 publications receiving 21966 citations. Previous affiliations of Lawrence L. Wald include Siemens & University of California, San Francisco.


Papers
More filters
Journal ArticleDOI
TL;DR: In this paper, the authors introduce a method to create interslice image shifts in the phase encoding direction to increase the distance between aliasing pixels, induced using sign-and amplitude-modulated slice-select gradient blips simultaneous with the EPI phase encoding blips.
Abstract: Simultaneous multislice Echo Planar Imaging (EPI) acquisition using parallel imaging can decrease the acquisition time for diffusion imaging and allow full-brain, high-resolution functional MRI (fMRI) acquisitions at a reduced repetition time (TR) However, the unaliasing of simultaneously acquired, closely spaced slices can be difficult, leading to a high g-factor penalty We introduce a method to create interslice image shifts in the phase encoding direction to increase the distance between aliasing pixels The shift between the slices is induced using sign- and amplitude-modulated slice-select gradient blips simultaneous with the EPI phase encoding blips This achieves the desired shifts but avoids an undesired "tilted voxel" blurring artifact associated with previous methods We validate the method in 3× slice-accelerated spin-echo and gradient-echo EPI at 3 T and 7 T using 32-channel radio frequency (RF) coil brain arrays The Monte-Carlo simulated average g-factor penalty of the 3-fold slice-accelerated acquisition with interslice shifts is <1% at 3 T (compared with 32% without slice shift) Combining 3× slice acceleration with 2× inplane acceleration, the g-factor penalty becomes 19% at 3 T and 10% at 7 T (compared with 41% and 23% without slice shift) We demonstrate the potential of the method for accelerating diffusion imaging by comparing the fiber orientation uncertainty, where the 3-fold faster acquisition showed no noticeable degradation

1,183 citations

Journal ArticleDOI
TL;DR: The results show that the atlas and companion segmentation method can segment T1 and T2 images, as well as their combination, replicate findings on mild cognitive impairment based on high-resolution T2 data, and can discriminate between Alzheimer's disease subjects and elderly controls with 88% accuracy.

862 citations

Journal ArticleDOI
TL;DR: By reducing the signal strength using higher image resolution, the ratio of physiologic to image noise could be reduced to a regime where increased sensitivity afforded by higher field strength still translated to improved SNR in the fMRI time-series.

622 citations

Journal ArticleDOI
TL;DR: The Human Connectome Project is to address limiting factors by re-engineering the scanner from the ground up to optimize the high b-value, high angular resolution diffusion imaging needed for sensitive and accurate mapping of the brain's structural connections by implementing a novel 4-port drive geometry and optimizing size and linearity for the brain.

479 citations

Journal ArticleDOI
TL;DR: Avoiding surface laminae improved spatial localization by about 40% at a cost of 36% in z-statistic, implying that optimal spatial resolution in functional imaging of the cortex can be achieved using anatomically-informed spatial sampling to avoid large pial vessels.

371 citations


Cited by
More filters
Journal ArticleDOI
TL;DR: A review of recent as well as classic image registration methods to provide a comprehensive reference source for the researchers involved in image registration, regardless of particular application areas.

6,842 citations

Journal ArticleDOI
TL;DR: In this paper, the organization of networks in the human cerebrum was explored using resting-state functional connectivity MRI data from 1,000 subjects and a clustering approach was employed to identify and replicate networks of functionally coupled regions across the cerebral cortex.
Abstract: Information processing in the cerebral cortex involves interactions among distributed areas. Anatomical connectivity suggests that certain areas form local hierarchical relations such as within the visual system. Other connectivity patterns, particularly among association areas, suggest the presence of large-scale circuits without clear hierarchical relations. In this study the organization of networks in the human cerebrum was explored using resting-state functional connectivity MRI. Data from 1,000 subjects were registered using surface-based alignment. A clustering approach was employed to identify and replicate networks of functionally coupled regions across the cerebral cortex. The results revealed local networks confined to sensory and motor cortices as well as distributed networks of association regions. Within the sensory and motor cortices, functional connectivity followed topographic representations across adjacent areas. In association cortex, the connectivity patterns often showed abrupt transitions between network boundaries. Focused analyses were performed to better understand properties of network connectivity. A canonical sensory-motor pathway involving primary visual area, putative middle temporal area complex (MT+), lateral intraparietal area, and frontal eye field was analyzed to explore how interactions might arise within and between networks. Results showed that adjacent regions of the MT+ complex demonstrate differential connectivity consistent with a hierarchical pathway that spans networks. The functional connectivity of parietal and prefrontal association cortices was next explored. Distinct connectivity profiles of neighboring regions suggest they participate in distributed networks that, while showing evidence for interactions, are embedded within largely parallel, interdigitated circuits. We conclude by discussing the organization of these large-scale cerebral networks in relation to monkey anatomy and their potential evolutionary expansion in humans to support cognition.

6,284 citations