John Drozd

Association between gait variability and brain ventricle attributes: a brain mapping study

BACKGROUND It remains unknown which brain regions are involved in the maintenance of gait dynamic stability in older adults, as characterized by a low stride time variability. Expansion of lateral cerebral ventricles is an indirect marker of adjacent brain tissue volume. The purpose of this study was to examine the association between stride time variability and the volume of sub-regions of the lateral cerebral ventricles among older community-dwellers. METHODS One-hundred-fifteen participants free of hydrocephalus from the GAIT study (mean, 70.4±4.4years; 43.5% female) were included in this analysis. Stride time variability was measured at self-selected pace with a 10m electronic portable walkway (GAITRite). Participants were separated into 3 groups based on tertiles of stride time variability (i.e., <2.0%; 2.0-2.8%; >2.8%). Brain ventricle sub-volumes were quantified from three-dimensional T1-weighted MRI using semi-automated software. Age, gender, Cumulative Illness Rating Scale for Geriatrics, Mini-Mental State Examination, Go-NoGo, brain vascular burden, 4-item Geriatric Depression Scale, psychoactive drugs, vision, proprioception, body mass index, muscular strength and gait velocity were used as covariates. RESULTS Participants with the highest (i.e., worst) tertile of stride time variability exhibited larger temporal horns than those with the lowest (P=0.030) and intermediate tertiles (P=0.028). They also had larger middle portions of ventricular bodies than those with the intermediate tertile (P=0.018). Larger temporal horns were associated with increase in stride time variability (adjusted β=0.86, P=0.005), specifically with the highest tertile of stride time variability (adjusted OR=2.45, P=0.044). CONCLUSIONS Higher stride time variability was associated with larger temporal horns in older community-dwellers. Addressing focal neuronal losses in temporal lobes may represent an important strategy to prevent gait instability.

A study of the orbits of the logarithmic potential for galaxies

The logarithmic potential is of great interest and relevance in the study of the dynamics of galaxies. Some small corrections to the work of Contopoulos & Seimenis who used the method of Prendergast to find periodic orbits and bifurcations within such a potential are presented. The solution of the orbital radial equation for the purely radial logarithmic potential is then considered using the precessing ellipse (p-ellipse) method pioneered by Struck. This differential orbital equation is a special case of the generalized Burgers equation. The apsidal angle is also determined, both numerically and analytically by means of the LambertW and the polylogarithmic functions. The use of these functions in computing the gravitational lensing produced by logarithmic potentials is discussed.

A novel MRI-compatible brain ventricle phantom for validation of segmentation and volumetry methods†

To create a standardized, MRI‐compatible, life‐sized phantom of the brain ventricles to evaluate ventricle segmentation methods using T1‐weighted MRI. An objective phantom is needed to test the many different segmentation programs currently used to measure ventricle volumes in patients with Alzheimers disease.

Automated algorithm to measure changes in medial temporal lobe volume in Alzheimer disease.

BACKGROUND The change in volume of anatomic structures is as a sensitive indicator of Alzheimer disease (AD) progression. Although several methods are available to measure brain volumes, improvements in speed and automation are required. Our objective was to develop a fully automated, fast, and reliable approach to measure change in medial temporal lobe (MTL) volume, including primarily hippocampus. METHODS The MTL volume defined in an atlas image was propagated onto each baseline image and a level set algorithm was applied to refine the shape and smooth the boundary. The MTL of the baseline image was then mapped onto the corresponding follow-up image to measure volume change (ΔMTL). Baseline and 24 months 3D T1-weighted images from the Alzheimer Disease Neuroimaging Initiative (ADNI) were randomly selected for 50 normal elderly controls (NECs), 50 subjects with mild cognitive impairment (MCI) and 50 subjects with AD to test the algorithm. The method was compared to the FreeSurfer segmentation tools. RESULTS The average ΔMTL (mean±SEM) was 68±35mm(3) in NEC, 187±38mm(3) in MCI and 300±34mm(3) in the AD group and was significantly different (p<0.0001) between all three groups. The ΔMTL was correlated with cognitive decline. COMPARISON WITH EXISTING METHOD(S) Results for the FreeSurfer software were similar but did not detect significant differences between the MCI and AD groups. CONCLUSION This novel segmentation approach is fully automated and provides a robust marker of brain atrophy that shows different rates of atrophy over 2 years between NEC, MCI, and AD groups.

A study of the gravitational wave form from pulsars

We present analytical and numerical studies of the Fourier transform (FT) of the gravitational wave (GW) signal from a pulsar, taking into account the rotation and orbital motion of the Earth. We also briefly discuss the Zak– Gelfand integral transform and a special class of the generalized hypergeometric function of potential relevance. The Zak–Gelfand integral transform that arises in our analytic approach has also been useful for Schr¨ odinger operators in periodic potentials in condensed matter physics (Bloch wavefunctions) and holds promise for the study of periodic GW signals for long integration times.

Development and application of pulmonary structure-function registration methods: towards pulmonary image-guidance tools for improved airway targeted therapies and outcomes

Objectives: We aimed to develop a way to rapidly generate multi-modality (MRI-CT) pulmonary imaging structurefunction maps using novel non-rigid image registration methods. This objective is part of our overarching goal to provide an image processing pipeline to generate pulmonary structure-function maps and guide airway-targeted therapies. Methods: Anatomical 1H and functional 3He MRI were acquired in 5 healthy asymptomatic ex-smokers and 7 ex-smokers with chronic obstructive pulmonary disease (COPD) at inspiration breath-hold. Thoracic CT was performed within ten minutes of MRI using the same breath-hold volume. Landmark-based affine registration methods previously validated for imaging of COPD, was based on corresponding fiducial markers located in both CT and 1H MRI coronal slices and compared with shape-based CT-MRI non-rigid registration. Shape-based CT-MRI registration was developed by first identifying the shapes of the lung cavities manually, and then registering the two shapes using affine and thin-plate spline algorithms. We compared registration accuracy using the fiducial localization error (FLE) and target registration error (TRE). Results: For landmark-based registration, the TRE was 8.4±5.3 mm for whole lung and 7.8±4.6 mm for the R and L lungs registered independently (p=0.4). For shape-based registration, the TRE was 8.0±4.6 mm for whole lung as compared to 6.9±4.4 mm for the R and L lung registered independently and this difference was significant (p=0.01). The difference for shape-based (6.9±4.4 mm) and landmark-based R and L lung registration (7.8±4.6 mm) was also significant (p=.04) Conclusion: Shape-based registration TRE was significantly improved compared to landmark-based registration when considering L and R lungs independently.

Simulations of collision times in gravity-driven granular flow

We use simulations to investigate collision time distributions as one approaches the static limit of steady-state flow of dry granular matter. The collision times fall in a power law distribution with an exponent dictated by whether the grains are ordered or disordered. Remarkably, the exponents have almost no dependence on dimension. We are also able to resolve a disagreement between simulation and experiments on the exponent of the collision time power law distribution.

A novel MRI-compatible brain ventricle phantom for validation of lateral ventricle segmentation programs

three cohorts (equal sample size) according to their rates of change in ADAS-Cog total scores. Patients with most positive rates of change in ADAS-cog total scores (i.e., worsening) showed significantly more rapid hippocampal atrophy as compared with to patients that showed the most negative rates of change in ADAS-Cog total scores (i.e., improving), and patients with intermediate, near-zero, rates of change in ADAS-cog total scores (i.e., stable) (trend). Conclusions: The rate of hippocampal degeneration may be altered in DAT patients who respond to treatment with memantine or donepezil as compared to patients who are treated with these drugs but who do not respond. However, we were not able to detect drug-specific changes in hippocampal degeneration. Cognitive improvement and slowing of disease progression in AD as a result of drug treatment may be dependent upon neuroanatomical factors that influence who will respond to treatment. Improving our understanding of these factors way lead to the development of more effective therapies.

Granular circulation in a cylindrical pan: simulations of reversing radial and tangential flows.

Granular flows due to simultaneous vertical and horizontal excitations of a flat-bottomed cylindrical pan are investigated using event-driven molecular dynamics simulations. In agreement with recent experimental results, we observe a transition from a solidlike state to a fluidized state in which circulatory flow occurs simultaneously in the radial and tangential directions. By going beyond the range of conditions explored experimentally, we find that each of these circulations reverses its direction as a function of the control parameters of the motion. We numerically evaluate the dynamical phase diagram for this system and show, using a simple model, that the solid-fluid transition can be understood in terms of a critical value of the radial acceleration of the pan bottom and that the circulation reversals are controlled by the phase shift relating the horizontal and vertical components of the vibrations. We also discuss the crucial role played by the geometry of the boundary conditions and point out a relationship of the circulation observed here and the flows generated in vibratory conveyors.