Generalized methods and solvers for noise removal from piecewise constant signals. I. Background theory

Removing noise from piecewise constant (PWC) signals is a challenging signal processing problem arising in many practical contexts. For example, in exploration geosciences, noisy drill hole records need to be separated into stratigraphic zones, and in biophysics, jumps between molecular dwell states have to be extracted from noisy fluorescence microscopy signals. Many PWC denoising methods exist, including total variation regularization, mean shift clustering, stepwise jump placement, running medians, convex clustering shrinkage and bilateral filtering; conventional linear signal processing methods are fundamentally unsuited. This paper (part I, the first of two) shows that most of these methods are associated with a special case of a generalized functional, minimized to achieve PWC denoising. The minimizer can be obtained by diverse solver algorithms, including stepwise jump placement, convex programming, finite differences, iterated running medians, least angle regression, regularization path following and coordinate descent. In the second paper, part II, we introduce novel PWC denoising methods, and comparisons between these methods performed on synthetic and real signals, showing that the new understanding of the problem gained in part I leads to new methods that have a useful role to play.

Generalized methods and solvers for noise removal from piecewise constant signals. II. New methods

Removing noise from signals which are piecewise constant (PWC) is a challenging signal processing problem that arises in many practical scientific and engineering contexts. In the first paper (part I) of this series of two, we presented background theory building on results from the image processing community to show that the majority of these algorithms, and more proposed in the wider literature, are each associated with a special case of a generalized functional, that, when minimized, solves the PWC denoising problem. It shows how the minimizer can be obtained by a range of computational solver algorithms. In this second paper (part II), using this understanding developed in part I, we introduce several novel PWC denoising methods, which, for example, combine the global behaviour of mean shift clustering with the local smoothing of total variation diffusion, and show example solver algorithms for these new methods. Comparisons between these methods are performed on synthetic and real signals, revealing that our new methods have a useful role to play. Finally, overlaps between the generalized methods of these two papers and others such as wavelet shrinkage, hidden Markov models, and piecewise smooth filtering are touched on.

Neonatal seizures and post-neonatal epilepsy:a seven-year follow-up study

BACKGROUND: Seizures are one of the most common symptoms of acute neurological disorders in newborns. This study aims at evaluating predictors of epilepsy in newborns with neonatal seizures. METHODS: we recruited consecutively eighty-five neonates with repeated neonatal video-EEG-confirmed seizures between Jan 1999 and Dec 2004. The relationship between clinical, EEG and ultrasound data in neonatal period and the development of post-neonatal epilepsy was investigated at 7 years of age. RESULTS: Fifteen patients (17.6%) developed post-neonatal epilepsy. Partial or no response to anticonvulsant therapy (OR 16.7, 95% CI: 1.8-155.8, p= .01; OR 47, 95% CI: 5.2-418.1, p<.01 respectively), severely abnormal cerebral ultrasound scan findings (OR: 5.4; 95% CI: 1.1-27.4; p<.04), severely abnormal EEG background activity (OR: 9.5; 95% CI: 1.6-54.2; p= .01) and the presence of status epilepticus (OR: 6.1; 95% CI: 1.8-20.3; p<.01) were found to be predictors of epilepsy. However, only the response to therapy seemed to be an independent predictor of post-neonatal epilepsy. CONCLUSION: Neonatal seizures seem to be related to post-neonatal epilepsy. Recurrent and prolonged neonatal seizures may act on an epileptogenic substrate, causing further damage, which is responsible for the subsequent clinical expression of epilepsy.

Reducing suffering in animal models and procedures involving seizures, convulsions and epilepsy

This report is based on discussions and submissions from an expert working group consisting of veterinarians, animal care staff and scientists with expert knowledge relevant to the field and aims to facilitate the implementation of the Three Rs (replacement, reduction and refinement) in the use of animal models or procedures involving seizures, convulsions and epilepsy. Each of these conditions will be considered, the specific welfare issues discussed, and practical measures to reduce animal use and suffering suggested. The emphasis is on refinement since this has the greatest potential for immediate implementation, and some general issues for refinement are summarised to help achieve this, with more detail provided on a range of specific refinements.

Generalized mean field approximation for parallel dynamics of the Ising model

The dynamics of the non-equilibrium Ising model with parallel updates is investigated using a generalized mean field approximation that incorporates multiple two-site correlations at any two time steps, which can be obtained recursively. The proposed method shows significant improvement in predicting local system properties compared to other mean field approximation techniques, particularly in systems with symmetric interactions. Results are also evaluated against those obtained from Monte Carlo simulations. The method is also employed to obtain parameter values for the kinetic inverse Ising modeling problem, where couplings and local field values of a fully connected spin system are inferred from data. © 2014 IOP Publishing Ltd and SISSA Medialab srl.

The value of magnetoencephalography to guide electrode implantation in epilepsy

To investigate if Magnetoencephalography (MEG) can add non-redundant information to guide implantation sites for intracranial recordings (IR). The contribution of MEG to intracranial recording planning was evaluated in 12 consecutive patients assessed pre-surgically with MEG followed by IR. Primary outcome measures were the identification of focal seizure onset in IR and favorable surgical outcome. Outcome measures were compared to those of 12 patients matched for implantation type in whom non-invasive pre-surgical assessment suggested clear hypotheses for implantation (non-MEG group). In the MEG group, non-invasive assessment without MEG was inconclusive, and MEG was then used to further help identify implantation sites. In all MEG patients, at least one virtual MEG electrode generated suitable hypotheses for the location of implantations. No differences in outcome measures were found between non-MEG and MEG groups. Although the MEG group included more complex patients, it showed similar percentage of successful implantations as the non-MEG group. This suggests that MEG can contribute to identify implantation sites where standard methods failed. © 2013 Springer Science+Business Media New York.

Psychiatric adverse effects of zonisamide in patients with epilepsy and mental disorder comorbidities

Over the last few years, zonisamide has been proposed as a potentially useful medication for patients with focal seizures, with or without secondary generalization. Since psychiatric adverse effects, including mania, psychosis, and suicidal ideation, have been associated with its use, it was suggested that the presence of antecedent psychiatric disorders is an important factor associated with the discontinuation of zonisamide therapy in patients with epilepsy. We, therefore, set out to assess the tolerability profile of zonisamide in a retrospective chart review of 23 patients with epilepsy and comorbid mental disorders, recruited from two specialist pediatric (n=11) and adult (n=12) neuropsychiatry clinics. All patients had a clinical diagnosis of treatment-refractory epilepsy after extensive neurophysiological and neuroimaging investigations. The vast majority of patients (n=22/23, 95.7%) had tried previous antiepileptic medications, and most adult patients (n=9/11, 81.8%) were on concomitant medication for epilepsy. In the majority of cases, the psychiatric adverse effects of zonisamide were not severe. Four patients (17.4%) discontinued zonisamide because of lack of efficacy, whereas only one patient (4.3%) discontinued it because of the severity of psychiatric adverse effects (major depressive disorder). The low discontinuation rate of zonisamide in a selected population of patients with epilepsy and neuropsychiatric comorbidity suggests that this medication is safe and reasonably well-tolerated for use in patients with treatment-refractory epilepsy. Given the limitations of the present study, including the relatively small sample size, further research is warranted to confirm this finding. © 2013 Elsevier Inc.

Magnetoencephalography in the study of epilepsy and consciousness

The neural bases of altered consciousness in patients with epilepsy during seizures and at rest have raised significant interest in the last decade. This exponential growth has been supported by the parallel development of techniques and methods to investigate brain function noninvasively with unprecedented spatial and temporal resolution. In this article, we review the contribution of magnetoencephalography to deconvolve the bioelectrical changes associated with impaired consciousness during seizures. We use data collected from a patient with refractory absence seizures to discuss how spike-wave discharges are associated with perturbations in optimal connectivity within and between brain regions and discuss indirect evidence to suggest that this phenomenon might explain the cognitive deficits experienced during prolonged 3/s spike-wave discharges. © 2013 Elsevier Inc.

Thesis submitted for the degree of Doctor of Science. Book by G.F.A Harding; P.M. Jeavons, Photosensitive Epilepsy also included.

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Photosensitive benign myoclonic epilepsy in infancy

Purpose: To describe the electroclinical features of subjects who presented with a photosensitive benign myoclonic epilepsy in infancy (PBMEI). Methods: The patients were selected from a group of epileptic subjects with seizure onset in infancy or early childhood. Inclusion criteria were the presence of photic-induced myoclonic seizures and a favorable outcome. Cases with less than 24 month follow up were excluded from the analysis. Results: Eight patients were identified (4 males, 4 females). Personal history was uneventful. All of them had familial antecedents of epilepsy. Psychomotor development was normal in 6 cases, both before and after seizure onset. One patient showed a mild mental retardation and a further patient showed some behavioral disturbances. Neuroradiological investigations, when performed (5 cases), gave normal results. The clinical manifestations were typical and could vary from upward movements of the eyes to myoclonic jerks of the head and shoulders, isolated or briefly repetitive, never causing a fall. Age of onset was between 11 months and 3 years and 2 months. Characteristically, the seizures were always triggered by photic stimulation. Non photo-induced spontaneous myoclonic attacks were reported in 2 cases during the follow-up. Other types of seizures were present at follow-up in 2 cases. The outcome was favorable, even if, usually, seizure control required high AED plasma levels. Since the clinical symptoms were not recognized early, some patients were treated only many years after the onset of symptoms. Conclusion: Among BMEI patients, our cases constitute a subgroup in which myoclonic jerks were always triggered by photostimulation, in particular at onset of their epilepsy. © 2006 International League Against Epilepsy.

A new fast generalized sphere decoding algorithm in MIMO systems

A new generalized sphere decoding algorithm is proposed for underdetermined MIMO systems with fewer receive antennas N than transmit antennas M. The proposed algorithm is significantly faster than the existing generalized sphere decoding algorithms. The basic idea is to partition the transmitted signal vector into two subvectors x and x with N - 1 and M - N + 1 elements respectively. After some simple transformations, an outer layer Sphere Decoder (SD) can be used to choose proper x and then use an inner layer SD to decide x, thus the whole transmitted signal vector is obtained. Simulation results show that Double Layer Sphere Decoding (DLSD) has far less complexity than the existing Generalized Sphere Decoding (GSDs).

Visually induced syncope:a nonepileptic manifestation of visual sensitivity?

Visual sensitivity, defined as the “susceptibility toward experiencing seizures, which are triggered by the physical characteristics of visual stimuli and not by their perceptual properties,”1 can manifest in the context of various forms of generalized or focal, idiopathic or symptomatic epilepsies.2 We report a patient with no family or personal history of epilepsy who presented episodes of loss of consciousness exclusively triggered by visual stimuli unrelated to their emotional content, in which we have documented EEG-EKG characteristics suggestive of a neurally mediated syncope.

Clinical utility of implantable neurostimulation devices as adjunctive treatment of uncontrolled seizures

About one third of patients with epilepsy are refractory to medical treatment. For these patients, alternative treatment options include implantable neurostimulation devices such as vagus nerve stimulation (VNS), deep brain stimulation (DBS), and responsive neurostimulation systems (RNS). We conducted a systematic literature review to assess the available evidence on the clinical efficacy of these devices in patients with refractory epilepsy across their lifespan. VNS has the largest evidence base, and numerous randomized controlled trials and open-label studies support its use in the treatment of refractory epilepsy. It was approved by the US Food and Drug Administration in 1997 for treatment of partial seizures, but has also shown significant benefit in the treatment of generalized seizures. Results in adult populations have been more encouraging than in pediatric populations, where more studies are required. VNS is considered a safe and well-tolerated treatment, and serious side effects are rare. DBS is a well-established treatment for several movement disorders, and has a small evidence base for treatment of refractory epilepsy. Stimulation of the anterior nucleus of the thalamus has shown the most encouraging results, where significant decreases in seizure frequency were reported. Other potential targets include the centromedian thalamic nucleus, hippocampus, cerebellum, and basal ganglia structures. Preliminary results on RNS, new-generation implantable neurostimulation devices which stimulate brain structures only when epileptic activity is detected, are encouraging. Overall, implantable neurostimulation devices appear to be a safe and beneficial treatment option for patients in whom medical treatment has failed to adequately control their epilepsy. Further large-scale randomized controlled trials are required to provide a sufficient evidence base for the inclusion of DBS and RNS in clinical guidelines.