Evan K. Curwood

Dynamic sample imaging in coherent diffractive imaging

As the resolution in coherent diffractive imaging improves, interexposure and intraexposure sample dynamics, such as motion, degrade the quality of the reconstructed image. Selecting data sets that include only exposures where tolerably little motion has occurred is an inefficient use of time and flux, especially when detector readout time is significant. We provide an experimental demonstration of an approach in which all images of a data set exhibiting sample motion are combined to improve the quality of a reconstruction. This approach is applicable to more general sample dynamics (including sample damage) that occur during measurement.

Brain regions with abnormal network properties in severe epilepsy of Lennox‐Gastaut phenotype: Multivariate analysis of task‐free fMRI

Lennox‐Gastaut syndrome, and the similar but less tightly defined Lennox‐Gastaut phenotype, describe patients with severe epilepsy, generalized epileptic discharges, and variable intellectual disability. Our previous functional neuroimaging studies suggest that abnormal diffuse association network activity underlies the epileptic discharges of this clinical phenotype. Herein we use a data‐driven multivariate approach to determine the spatial changes in local and global networks of patients with severe epilepsy of the Lennox‐Gastaut phenotype.

Mapping granular structure in the biological adhesive of Phragmatopoma californica using phase diverse coherent diffractive imaging

This paper demonstrates the application of the high sensitivity, low radiation dose imaging method recently presented as phase diverse coherent diffraction imaging, to the study of biological and other weakly scattering samples. The method is applied, using X-ray illumination, to quantitative imaging of the granular precursors of underwater adhesive produced by the marine sandcastle worm, Phragmatopoma californica. We are able to observe the internal structure of the adhesive precursors in a number of states.

Tract-specific atrophy in focal epilepsy: Disease, genetics, or seizures?

To investigate whether genetics, underlying pathology, or repeated seizures contribute to atrophy in specific white matter tracts.

X-ray laser–induced electron dynamics observed by femtosecond diffraction from nanocrystals of Buckminsterfullerene

Coherent electron dynamics in a periodic array of C60 molecular targets driven by intense x-ray pulses of femtosecond duration. X-ray free-electron lasers (XFELs) deliver x-ray pulses with a coherent flux that is approximately eight orders of magnitude greater than that available from a modern third-generation synchrotron source. The power density of an XFEL pulse may be so high that it can modify the electronic properties of a sample on a femtosecond time scale. Exploration of the interaction of intense coherent x-ray pulses and matter is both of intrinsic scientific interest and of critical importance to the interpretation of experiments that probe the structures of materials using high-brightness femtosecond XFEL pulses. We report observations of the diffraction of extremely intense 32-fs nanofocused x-ray pulses by a powder sample of crystalline C60. We find that the diffraction pattern at the highest available incident power significantly differs from the one obtained using either third-generation synchrotron sources or XFEL sources operating at low output power and does not correspond to the diffraction pattern expected from any known phase of crystalline C60. We interpret these data as evidence of a long-range, coherent dynamic electronic distortion that is driven by the interaction of the periodic array of C60 molecular targets with intense x-ray pulses of femtosecond duration.

The dynamics of functional connectivity in neocortical focal epilepsy

Focal epilepsy is characterised by paroxysmal events, reflecting changes in underlying local brain networks. To capture brain network activity at the maximal temporal resolution of the acquired functional magnetic resonance imaging (fMRI) data, we have previously developed a novel analysis framework called Dynamic Regional Phase Synchrony (DRePS). DRePS measures instantaneous mean phase coherence within neighbourhoods of brain voxels. We use it here to examine how the dynamics of the functional connections of regional brain networks are altered in neocortical focal epilepsy. Using task-free fMRI data from 21 subjects with focal epilepsy and 21 healthy controls, we calculated the power spectral density of DRePS, which is a measure of signal variability in local connectivity estimates. Whole-brain averaged power spectral density of DRePS, or signal variability of local connectivity, was significantly higher in epilepsy subjects compared to healthy controls. Maximal increase in DRePS spectral power was seen in bilateral inferior frontal cortices, ipsilateral mid-cingulate gyrus, superior temporal gyrus, caudate head, and contralateral cerebellum. Our results provide further evidence of common brain abnormalities across people with focal epilepsy. We postulate that dynamic changes in specific cortical brain areas may help maintain brain function in the presence of pathological epileptiform network activity in neocortical focal epilepsy.

Default mode network neurodegeneration reveals the remote effects of ischaemic stroke

Dementia is estimated to occur in 15%–30% patients after ischaemic stroke.1 Stroke may initiate or accelerate neurodegeneration associated with cognitive impairment.1 Brain atrophy is an important marker of neurodegeneration, preceding the emergence of cognitive symptoms in Alzheimer’s disease (AD).2 Atrophy occurs in distributed regions that collectively mirror known brain networks, including the default mode network (DMN). Atrophy and dysfunction within the DMN is evident in healthy ageing, accelerated in pathological ageing2 and evident in acute and subacute stroke.3 Lesion location rarely predicts long-term outcome in stroke. Network-wide changes may better explain neurodegeneration and conversion to dementia after stroke. Atrophy after stroke has not been well investigated and has been limited to cross-sectional studies and regional volume changes. Structural covariance is an increasingly popular method of examining network-wide correlations in morphometric estimates of brain structure, such as cortical thickness or grey matter volume. There is a close relationship between estimates of network-based structural covariance and intrinsic functional network architecture.4 Structural covariance can be tracked over time to reveal changes in brain organisation, either developmental or degenerative, via cross-sectional comparisons within and between groups.4 Cross-sectional differences can be difficult to detect when there is normal variability across individuals.5 Longitudinal imaging has the benefit of overcoming interindividual differences in cortical morphology by using each individual as their own control.5 Longitudinal imaging also provides an opportunity for more direct examination of atrophy within networks by looking at correlations in the rate of cortical atrophy (see figure 1 in the online Supplementary file 1) across the brain, rather than just correlations in the morphometric measure itself. Atrophy across the brain can also be examined by …

Abnormal cortical thickness connectivity persists in childhood absence epilepsy

Childhood absence epilepsy (CAE) is a childhood‐onset generalized epilepsy. Recent fMRI studies have suggested that frontal cortex activity occurs before thalamic involvement in epileptic discharges suggesting that frontal cortex may play an important role in childhood absence seizures. Neurocognitive deficits can persist after resolution of the epilepsy. We investigate whether structural connectivity changes are present in the brains of CAE patients in young adulthood.

Pontine and cerebral atrophy in Lennox-Gastaut syndrome.

OBJECTIVES Lennox-Gastaut syndrome (LGS) is a severe epilepsy of childhood onset associated with intellectual disability and multiple seizure types. Characteristic interictal electrographic discharges include generalized paroxysmal fast activity and slow spike and wave, which we have previously shown recruit widespread areas of association cortex. We wished to determine whether patients with Lennox-Gastaut syndrome (LGS) have changes in cerebral volumes that match this pattern of cortical recruitment. METHODS High resolution T1 weighted structural MRI was collected from 10 patients with LGS and 10 age and sex matched controls. Voxel-based morphometry (VBM) was used to compare tissue volumes across the whole brain (grey matter, white matter and CSF) and pontine volume between patients and controls, as well as to identify other regions of maximal tissue loss. RESULTS LGS patients showed a significant decrease in whole brain volume compared to controls. Cortical atrophy was prominent in the mesial frontal region and bilateral anterior temporal poles. White matter atrophy was widespread and included peri-central and premotor regions. Atrophy was prominent in the pons, particularly in the region of the reticular formation. Grey matter atrophy trended to progress with age. SIGNIFICANCE Grey and white matter atrophy are a feature of Lennox-Gastaut syndrome. Grey matter atrophy is apparent in the mesial frontal lobe suggesting this region may be an important node in the epilepsy network of LGS. Atrophy maximal in the pons and cerebellum mimics the patterns of seizure spread that has been previously observed during tonic seizures. This supports the idea that the pons is a key part of the epilepsy network in LGS.