ECG fingerprints of obstructed breathing in sleep apnea patients

This article aims to identify the potential indicators of obstructive apnea (OA) in the ECG, based on the traces of QRS area from multiple ECG leads. We compare the difference in these traces' phase relation found during and after each OA episode to the difference between the first and second half of the OA and between split halves of epochs of normal respiration (NR).     

Single-sweep analysis of event-related potentials by waveletnetworks-methodological basis and clinical application

OBJECTIVE: Trial-to-trial variabilities in event-related potentials (ERP's), which are neglected by investigating averaged ERP's, can be important to establish group-specific effects in clinical studies. Single ERP responses have to be analyzed to quantify these variations. In order to overcome the disadvantages of existing single-sweep estimators, we have developed a new procedure based on wavelet networks (WN's) and applied this novel approach in a study concerning attention deficit hyperactivity disorder (ADHD) in children. METHOD: WN's represent signals as a linear combination of wavelet nodes, i.e., components characterized by time-frequency features related to the wavelet transformation. In single-sweep analysis, each wavelet node is restricted to a specific region of the time-frequency plane during the recursive WN training process. This is achieved by means of tapering and bandpass filtering with Gaussian functions which are automatically adapted and closely related to the Morlet basis wavelet. The time course of a single event-related response can be reliably estimated. Furthermore, the WN method automatically provides well-defined parameters for single event-related responses, respectively ERP trial-to-trial variabilities. RESULTS: In a psychophysiological study on ADHD using auditory evoked potentials (AEP's), latency and amplitude parameters extracted from averaged ERP's did not reveal any significant differences between 25 control and 25 ADHD boys. In contrast, interesting group-specific differences could be established by WN single-sweep analysis. CONCLUSION: WN single-sweep analysis can be recommended as a sensitive tool for clinical ERP studies which should be applied in addition to the investigation of averaged responses. INDEX TERMS: Attention deficit hyperactivity disorder (ADHD), event-related potentials, single-sweep estimation, single-sweep parameterization, time-frequency method, wavelet networks.     

Detecting chaos in HRV signals in human cardiac transplant recipients

Infections with organisms of the genus Bartonella, for many years important only in South and Central America, have assumed significance in developing countries, especially in conjunction with the advent of the pandemic of the human immunodeficiency virus infection. New molecular and culture techniques have determined that these organisms cause new diseases such as bacillary angiomatosis as well as diseases the etiology of which have been unknown such as cat scratch disease. In this article, the microbiology, pathogenesis, histopathology and clinical manifestations of diseases caused by these organisms are discussed.     

Classifying biosignals with wavelet networks [a method fornoninvasive diagnosis]

In recent years, a particular challenge has arisen in noninvasive medical diagnostic procedures. Because biosignals recorded on the body surface reflect the internal behaviour and status of the organism or its parts, they are ideally suited to provide essential information of these organs to the clinician without any invasive measures. But how are the recorded time courses of the signals to be interpreted with regard to a diagnostic decision? What are the essential features and in what code is the information hidden in the signals? These questions are typical of so-called pattern-recognition tasks. This article reviews pattern recognition as it applies to medical diagnostics and discusses the concept of wavelet networks as a means of biosignal classification. An example is presented in which this approach was used for classifying preprocessed ECG signals to identify patients who were at high-risk of developing ventricular tachycardia (VT)     

A flexible registration and evaluation engine (f.r.e.e.)

We present an image registration framework which offers effective assistance for solving current registration problems. This work was motivated by the huge amount of registration problems in clinical applications and the problem of finding adequate solutions and properly comparing them. We have therefore designed a framework that supports the establishment, evaluation and comparison of registration approaches. Flexible registration and evaluation engine (f.r.e.e.) achieves a broad basis of algorithms by utilizing the insight segmentation and registration toolkit (ITK). This basis can be extended by virtually any new approach or algorithm, which then becomes seamlessly integrated into the method set of the f.r.e.e. framework. The framework offers suitable tools for an easy integration, optimization and proper evaluation of registration approaches, as well as an efficient utilization of the results in clinical routine. The framework is currently being evaluated at the Heidelberg University Hospital, Germany. The first results were gathered with an application implemented for the Neurosurgical Department of the hospital. In these tests the framework concept, along with its specific tools, was very promising for establishing clinical applications (e.g. preoperative neurosurgical planning; registration of cardiac images) and therefore motivated further development. The ability to automatically optimize the parameterization of registration methods regarding a given test set also proved useful, allowing more concentration on scientific problems themselves and not on the laborious task of parameter tweaking. Due to implemented abstraction layers, f.r.e.e. also allows a high degree of transparency and thus good comparability of registration approaches and results.     

Platelet serotonin and interleukin-1 beta after sleep deprivation and recovery sleep in humans

Sleep deprivation (SD) represents a well-established therapy for major depression. Recent findings suggest that the antidepressive effects of sleep deprivation are mediated at least in part by pro-serotoninergic mechanisms. Furthermore, SD has been demonstrated to modify different host defense activities. We therefore investigated the serotonin (5-HT) content in platelets, platelet density distribution and 5-HT-induced IL-1 beta release from platelets in 10 healthy men before and after total SD (TSD) as well as after recovery sleep. Blood samples were drawn on 3 consecutive days at 7.00 h, 13.00 h, and 19.00 h, respectively. In addition, the psychophysiological parameters tiredness and wakefulness were assessed. After TSD the normal daily variation of IL-1 beta release with high morning levels and low evening levels was found to be significantly inverted. The release of IL-1 beta corresponded positively to the subjectively experienced tiredness of the probands. Analysis of platelet density distribution indicated a significant daily variation of low density platelets with low levels in the morning and high levels in the evening, which was absent after TSD. Our findings favour an increased pro-serotoninergic effect after TSD, which comprises respective variations of the host defense system, but is abolished by consecutive recovery sleep.     

Direct suppression of Stat1 function during adenoviral infection

The phenomenon of enhanced backscatter from myocardial contrast agents was studied using two examples, a robust thicker-walled, intra-arterial agent (AIP 201) and a smaller thinner-walled, intravenous agent (Quantison). Both agents are composed of albumin-encapsulated microbubbles. Samples of the agents were inserted into an in vitro phantom and insonated under different scanning regimes. Upon insonation, Quantison exhibited a pronounced increase in mean backscatter at medium and low concentrations, which decreased dramatically with increasing number of frames of insonation. At high concentrations, no dramatic decrease or increase in mean backscatter was observed over the period of the experiment. AIP 201 exhibited an overall decrease in mean backscatter with increasing number of frames of insonation. These results suggest that the difference in size and wall thickness of the contrast microcapsules can significantly affect the behaviour of the contrast agents in an ultrasound field.     

Automated sleep stage identification system based on time-frequency analysis of a single EEG channel and random forest classifier

In this work, an efficient automated new approach for sleep stage identification based on the new standard of the American academy of sleep medicine (AASM) is presented. The propose approach employs time-frequency analysis and entropy measures for feature extraction from a single electroencephalograph (EEG) channel. Three time-frequency techniques were deployed for the analysis of the EEG signal: Choi-Williams distribution (CWD), continuous wavelet transform (CWT), and Hilbert-Huang Transform (HHT). Polysomnographic recordings from sixteen subjects were used in this study and features were extracted from the time-frequency representation of the EEG signal using Renyi's entropy. The classification of the extracted features was done using random forest classifier. The performance of the new approach was tested by evaluating the accuracy and the kappa coefficient for the three time-frequency distributions: CWD, CWT, and HHT. The CWT time-frequency distribution outperformed the other two distributions and showed excellent performance with an accuracy of 0.83 and a kappa coefficient of 0.76.     

Artefacts in magnetic resonance imaging caused by dental material

A common problem in computer tomography (CT) based imaging of the oral cavity is artefacts caused by dental restorations. The aim of this study was to investigate whether magnetic resonance imaging (MRI) of the oral cavity would be less affected than CT by artefacts caused by typical dental restorative alloys. In order to assess the extent of artefact generation, corresponding MRI scans of the same anatomic region with and without dental metal restorations were matched using a stereotactic frame. MRI imaging of the oral and maxillofacial region could be performed without reduction of the image quality by metallic dental restorations made from titanium, gold or amalgam. Dental restorations made from titanium, gold or amalgam did not reduce the image quality of the MRI sequence used in imaging of the oral and maxillofacial region for dental implant planning. In this respect MRI is superior to CT in implant planning.