February 6, 2013

Record 1 of 6.

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Title:

A Method for Estimating Zero-Flow Pressure and Intracranial Pressure

Author Full Names:

Marzban, Caren; Illian, Paul R.; Morison, David; Moore, Anne; Kliot, Michel; Czosnyka, Marek; Mourad, Pierre D.

Source:

JOURNAL OF NEUROSURGICAL ANESTHESIOLOGY, 25 (1):25-32; 10.1097/ANA.0b013e318263c295 JAN 2013

Abstract:

Background: It has been hypothesized that the critical closing pressure of cerebral circulation, or zero-flow pressure (ZFP), can estimate intracranial pressure (ICP). One ZFP estimation method used extrapolation of arterial blood pressure as against blood-flow velocity. The aim of this study was to improve ICP predictions.
Methods: Two revisions have been considered: (1) the linear model used for extrapolation is extended to a nonlinear equation; and (2) the parameters of the model are estimated by an alternative criterion (not least squares). The method is applied to data on transcranial Doppler measurements of blood-flow velocity, arterial blood pressure, and ICP from 104 patients suffering from closed traumatic brain injury, sampled across the United States and England.
Results: The revisions lead to qualitative (eg, precluding negative ICP) and quantitative improvements in ICP prediction. While moving from the original to the revised method, the +/- 2 SD of the error is reduced from 33 to 24 mm Hg, and the root-mean-squared error is reduced from 11 to 8.2 mm Hg. The distribution of root-mean-squared error is tighter as well; for the revised method the 25th and 75th percentiles are 4.1 and 13.7 mm Hg, respectively, as compared with 5.1 and 18.8 mm Hg for the original method.
Conclusions: Proposed alterations to a procedure for estimating ZFP lead to more accurate and more precise estimates of ICP, thereby offering improved means of estimating it noninvasively. The quality of the estimates is inadequate for many applications, but further work is proposed, which may lead to clinically useful results.

Record 2 of 6.

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Title:

Beta amyloid, tau, neuroimaging, and cognition: sequence modeling of biomarkers for Alzheimer's Disease

Author Full Names:

Han, S. Duke; Gruhl, Jonathan; Beckett, Laurel; Dodge, Hiroko H.; Stricker, Nikki H.; Farias, Sarah; Mungas, Dan

Group Author(s):

Alzheimer's Dis Neuroimaging

Source:

BRAIN IMAGING AND BEHAVIOR, 6 (4):610-620; 10.1007/s11682-012-9177-0 DEC 2012

Abstract:

Alzheimer's disease (AD) is associated with a cascade of pathological events involving formation of amyloid-based neuritic plaques and tau-based neurofibrillary tangles, changes in brain structure and function, and eventually, cognitive impairment and functional disability. The precise sequence of when each of these disease markers becomes abnormal is not yet clearly understood. The present study systematically tested the relationship between classes of biomarkers according to a proposed model of temporal sequence by Jack et al. (Lancet Neurology 9:119-128, 2010). We examined temporal relations among four classes of biomarkers: CSF A beta, CSF tau, neuroimaging variables (hippocampal volume, ventricular volume, FDG PET), and cognitive variables (memory and executive function). Random effects modeling of longitudinal data obtained from the Alzheimer's Disease Neuroimaging Initiative (ADNI) was used to test hypotheses that putative earlier markers of AD predicted change in lat! er markers, and that intervening markers reduced effects of earlier on later markers. Specifically, we hypothesized that CSF tau would explain CSF A beta's relation to neuroimaging and cognitive variables, and neuroimaging variables would explain tau's relation to cognitive variables. Consistent with hypotheses, results indicated that CSF A beta effects on cognition change were substantially attenuated by CSF tau and measures of brain structure and function, and CSF tau effects on cognitive change were attenuated by neuroimaging variables. Contrary to hypotheses, CSF A beta and CSF tau were observed to have independent effects on neuroimaging and CSF tau had a direct effect on baseline cognition independent of brain structure and function. These results have implications for clarifying the temporal sequence of AD changes and corresponding biomarkers.

Record 3 of 6.

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Title:

CSF biomarker associations with change in hippocampal volume and precuneus thickness: implications for the Alzheimer's pathological cascade

Author Full Names:

Stricker, Nikki H.; Dodge, Hiroko H.; Dowling, N. Maritza; Han, S. Duke; Erosheva, Elena A.; Jagust, William J.

Group Author(s):

Alzheimer's Dis Neuroimaging

Source:

BRAIN IMAGING AND BEHAVIOR, 6 (4):599-609; 10.1007/s11682-012-9171-6 DEC 2012

Abstract:

Neurofibrillary tangles (NFT) and amyloid plaques are hallmark neuropathological features of Alzheimer's disease (AD). There is some debate as to which neuropathological feature comes first in the disease process, with early autopsy studies suggesting that NFT develop first, and more recent neuroimaging studies supporting the early role of amyloid beta (A beta) deposition. Cerebrospinal fluid (CSF) biomarkers of A beta(42) and hyperphosphorylated tau (p-tau) have been shown to serve as in vivo proxy measures of amyloid plaques and NFT, respectively. The aim of this study was to examine the association between CSF biomarkers and rate of atrophy in the precuneus and hippocampus. These regions were selected because the precuneus appears to be affected early and severely by A beta deposition, and the hippocampus similarly by NFT pathology. We predicted (1) baseline A beta(42) would be related to accelerated rate of cortical thinning in the precuneus and volume loss in the hippoc! ampus, with the latter relationship expected to be weaker, (2) baseline p-tau(181p) would be related to accelerated rate of hippocampal atrophy and cortical thinning in the precuneus, with the latter relationship expected to be weaker. Using all ADNI cohorts, we fitted separate linear mixed-effects models for changes in hippocampus and precuneus longitudinal outcome measures with baseline CSF biomarkers modeled as predictors. Results partially supported our hypotheses: Both baseline p-tau(181p) and A beta(42) were associated with hippocampal atrophy over time. Neither p-tau(181p) nor A beta(42) were significantly related to cortical thinning in the precuneus over time. However, follow-up analyses demonstrated that having abnormal levels of both A beta(42) and p-tau(181p) was associated with an accelerated rate of atrophy in both the hippocampus and precuneus. Results support early effects of A beta in the Alzheimer's disease process, which are less apparent than and perhaps! dependent on p-tau effects as the disease progresses. However! , amyloi d deposition alone may be insufficient for emergence of significant morphometric changes and clinical symptoms.

Record 4 of 6.

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Title:

DIRICHLET HEAT KERNEL ESTIMATES FOR Delta(alpha/2) + Delta(beta/2)

Author Full Names:

Chen, Zhen-Qing; Kim, Panki; Song, Renming

Source:

ILLINOIS JOURNAL OF MATHEMATICS, 54 (4):1357-1392; SI WIN 2012

Abstract:

For d >= 1 and 0 < beta < alpha < 2, consider a family of pseudo differential operators {Delta(alpha) + a(beta) Delta(beta/2); a is an element of [0, 1]} on R-d that evolves continuously from Delta(alpha/2) to Delta(alpha/2) + Delta(beta/2). It gives arise to a family of Levy processes {X-a, a is an element of [0, 1]} on R-d, where each X-a is the independent sum of a symmetric alpha-stable process and a symmetric beta-stable process with weight a. For any C-1,C-1 open set D subset of R-d, we establish explicit sharp two-sided estimates, which are uniform in a is an element of (0,1], for the transition density function of the subprocess X-a,X-D of X-a killed upon leaving the open set D. The infinitesimal generator of X-a,X-D is the nonlocal operator Delta(alpha) + a(beta) Delta(beta/2) with zero exterior condition on D-c. As consequences of these sharp heat kernel estimates, we obtain uniform sharp Green function estimates for X-a,X-D and uniform boundary Harnack! principle for X-a in D with explicit decay rate.

Record 5 of 6.

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Title:

NONUNIQUENESS FOR NONNEGATIVE SOLUTIONS OF PARABOLIC STOCHASTIC PARTIAL DIFFERENTIAL EQUATIONS

Author Full Names:

Burdzy, K.; Mueller, C.; Perkins, E. A.

Source:

ILLINOIS JOURNAL OF MATHEMATICS, 54 (4):1481-1507; SI WIN 2012

Abstract:

Pathwise nonuniqueness is established for nonnegative solutions of the parabolic stochastic pde
partial derivative X/partial derivative t = Delta/2X + X-p(W) over dot + psi, X-0 equivalent to 0
where (W) over dot is a white noise, psi >= 0 is smooth, compactly supported and nontrivial, and 0 <p < 1/2. We further show that any solution spends positive time at the 0 function.

Record 6 of 6.

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Title:

Displaying Economic Value

Author Full Names:

Marzban, Caren

Source:

WEATHER AND FORECASTING, 27 (6):1604-1612; 10.1175/WAF-D-11-00138.1 DEC 2012

Abstract:

The distinction between forecast quality and economic value in a cost loss formulation is well known. Also well known is their complex relationship, even with some instances of a reversal between the two, where higher quality is associated with lower economic value, and vice versa. It is reasonable to expect such counterintuitive results when forecast quality and economic value both, multifaceted quantities are summarized by single scalar measures. Diagrams are often used to display forecast quality in order to better represent the multidimensional nature of forecast quality. Here, it is proposed that economic value be displayed as a region on a plot of hit rate versus false-alarm rate. Such a display obviates any need to summarize economic value by a scalar measure. The choice of the axes is motivated by the relative operating characteristic (ROC) diagram, and, so, this manner of displaying economic value is useful for deterministic as well as probabilistic forecasts.