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Biomedical subjects

H Dickhaus

Publications and source records attributed to H Dickhaus.

At least 19 recordsLinked to original sources
PubMed2005

Geometric accuracy of magnetic resonance imaging of the mandibular nerve.

OBJECTIVES: Magnetic resonance imaging (MRI) is not routinely used for dental implant planning. A prerequisite for dental implant planning is the accurate imaging of risk structures like the mandibular nerve. The geometric accuracy of the imaging of the mandibular nerve was investigated. METHODS: Two human cadaver heads were scanned using MRI. Computed tomography (CT) scans of the same heads were used as a benchmark. Using a stereotactic frame, corresponding images of MRI and CT were superimposed and the concordance of the images of the mandibular nerve in MRI with those of the mandibular canal in CT was assessed. RESULTS: The geometric accuracy of the mandibular nerve in MRI was as good as that of the mandibular canal in CT imaging. CONCLUSIONS: MRI of the mandibular nerve is sufficiently accurate for the use of this imaging method in dental implant planning.

Artifacts↗
PubMed2002

[Computer-assisted system for analysis of heart rate variability in clinical studies].

This paper describes an adaptable framework that facilitates exploratory analysis, interpretation and classification of beat-to-beat data extracted from the electrocardiogram (ECG). The system supports a variety of user-defined annotations and allows the definition of analysis programs. Special care is taken on the correct treatment of corrupted and missing data, ubiquitously found in real world problems. Besides the computation, the performance of single features can be inspected using different kinds of diagrams provided by the system. Combinations of features can be evaluated using a polynomial classifier. Both the computation and combination of features are defined as tasks that can be dispatched by a server to various clients. The framework is easily adaptable to different problem structures and has been used successfully in three studies.

Atrial Fibrillation↗
PubMed2002

[A computer system for planning and carrying out neurosurgical interventions].

Neurosurgical interventions have to be planned carefully using different sources of information like anatomical MR images, segmented brain structures, functional data (EEG, MEG, fMRI) and atlas information. We developed a 3D planning system that incorporates this important data. The planning procedure is performed by the neurosurgeon in less than 15 minutes. The results of the planning phase, i.e. an optimal trajectory, localizations of the electrical sources and information about the brain tissue can be used intraoperatively. Therefore the planning system is connected with a navigation system. The simultaneous visualization of the planning information and the actual position of the instrument during the surgical procedure is extremely valuable for the outcome and quality of the intervention.

Brain Neoplasms↗
PubMed2001

Time-on-task analysis using wavelet networks in an event-related potential study on attention-deficit hyperactivity disorder.

OBJECTIVE: The aim of this event-related potential (ERP) study was to test time-on-task analysis at the level of single sweeps in a clinical trial. Since inattentiveness is one of the main symptoms of attention-deficit hyperactivity disorder (ADHD), this child psychiatric disorder was chosen as an exemplary application. METHODS: Twenty-four healthy and 24 ADHD boys, aged 9--15 years, performed an auditory selective attention task for about 5 min. ERP single trials were analyzed using wavelet networks. Time-on-task analysis was applied to omission errors, reaction time and slow ERP components (frontal negativity, parietal positivity), represented by a low-frequency wavelet component. RESULTS: Both performance and ERP measures showed distinct temporal dynamics. Time-on-task effects were not only linear, but also of higher order and started after less than 1 min. For ADHD children, earlier time-on-task effects, i.e. an earlier increase of omission errors and frontal negativity, resulted. Healthy children could allocate more attentional resources during the course of the experiment. CONCLUSION: Time-on-task analysis at the level of single trials revealed phenomena probably reflecting ADHD children's attentional deficits. Thus, a more differentiated ERP analysis may provide a better understanding of the pathophysiological background in neuropsychiatric disorders.

Acoustic Stimulation↗
PubMed1999

Single-sweep analysis of event-related potentials by wavelet networks--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.

Adolescent↗
PubMed1997

Detecting chaos in HRV signals in human cardiac transplant recipients.

A statistical approach to chaos identification in time series is presented. The method is applied to numerical data generated by chaotic systems and to heart rate variability (HRV) signals of normal subjects and heart transplant recipients. This method compares the short-term predictability for a given time series to an ensemble of random data which has the same Fourier spectrum as the original time series. The short-term prediction error is computed as a discriminating statistic for performing statistical hypothesis testing. The results suggest that HRV signals of the transplant recipients recorded 3 months after the transplantations show the same signature of chaos as that of the HRV signals for normal subjects.

Algorithms↗
PubMed1997

EP parametrization and classification using wavelet networks--theoretical concept and medical application.

The purpose of this paper is to outline the fundamental concept of wavelet networks (WNs) and to demonstrate its specific advantages in a clinical discrimination task. A group of 25 boys with attention deficit hyperactivity disorder (ADHD) should be separated from a control group of 25 healthy boys by auditory evoked potentials. Because of the high variability of the recorded EP signals quantification of the averaged sweeps by peak latencies and amplitudes failed. However, with wavelet networks a maximum classification rate of 80% was achieved by crossvalidation. A WN is basically described as a multilayer perceptron which consists of two parts for feature extraction/parametrization and classification. These essential steps of a pattern recognition task are not separated in different tasks but linked together by the clamp of the learning algorithm. Because no user interaction is necessary we call this procedure a self-learning method.

Arousal↗
PubMed1995

Computer assisted bone age assessment.

Skeletal or bone age assessment is a very common and important task in the pediatric radiology. To estimate the bone age, visual methods are used which are strongly physician dependent and time-consuming. In order to overcome these disadvantages computerization of bone analysis is being tried. In this paper an approach for computer assisted bone age assessment is presented which tries to take typical computer capabilities into advantage by the concept of pattern recognition.

Age Determination by Skeleton↗
PubMed1994

Quantification of ECG late potentials by wavelet transformation.

Late potentials of preprocessed ECG recordings from patients with sustained ventricular tachycardia and healthy control subjects are investigated by the wavelet transformation. The advantages of this non-stationary signal processing method are discussed in comparison with FFT spectrograms of artificial test signals. The energy distribution plots of these wavelet transformed test signals demonstrate the superiority in detection accuracy and frequency resolution compared with the corresponding spectrograms. For this reason a quantitative discrimination between the two clinical groups of patients and healthy subjects was performed by calculating the scalograms of the wavelet transformed ECG signals in the time-frequency plane. The energy in the frequency band of 100-300 Hz during the last time segment of the QRS complex yielded best classification results.

Action Potentials↗
PubMed1994

Time-frequency analysis of ventricular late potentials.

The time-frequency characteristics are studied of averaged and filtered ECG records from 21 patients with sustained ventricular tachycardia and 29 healthy control subjects. Simulated data as well as real ECG records reveal the detection accuracy of the wavelet transform of signals with late potentials. The wavelet-transforms of preprocessed ECG signals are plotted in the time-frequency plane. These representations of the signals are well suited to describe the different characteristics of the patients and healthy subjects. A quantitative discrimination was performed with a sensitivity of 90% and a specificity of 72% by the energy underneath the squared modulus of the time-frequency distribution plots of the computed wavelet transforms.

Cardiac Pacing, Artificial↗
PubMed1994

A comparative summary of six Health/Medical Informatics programs.

This paper tries to compare six Health Informatics/Medical Informatics (HI/MI) programs by a number of attributes in standardized form. The different programs and their curricula were summarized at the 5th IMIA Working Conference on HI/MI Education at Heidelberg/Heilbronn. The presentation is condensed to a synoptical scheme. Most of the information used for this purpose is taken from five individual papers about the programs presented in this special issue of Methods of Information in Medicine.

Curriculum↗
PubMed1993

Heart rate variability in time and frequency domains: effects of gallopamil, nifedipine, and metoprolol compared with placebo.

OBJECTIVE: To assess the effects of three different antianginal drugs on heart rate, blood pressure, and heart rate variability. DESIGN: Randomised, single blind, placebo controlled, cross over study. SETTING: University hospital. PARTICIPANTS: Nine healthy male volunteers. INTERVENTIONS: Oral administration of either 50 mg gallopamil, 20 mg nifedipine, 100 mg metoprolol, or placebo according to a random crossover plan. MAIN OUTCOME MEASURES: Time intervals between consecutive R waves in electrocardiograms measured with an accuracy of 5 ms from digital Holter recordings. Blood pressure monitored continuously by finger plethysmography. RESULTS: Metoprolol lowered heart rate from 62(6) to 51(5) beats/min (p = 0.003) after 78(23) minutes. Nifedipine provoked reflex tachycardia from 56(5) to 94(18) beats/min (p < 0.001) at 10(3) minutes after treatment followed by an exponential decline in heart rate to baseline values with a time constant of 34(7) min in seven subjects but 83 minutes in one volunteer. One subject showed no exponential decline in heart rate. Nifedipine significantly lowered the supine mean arterial pressure from 86(6) to 67(6) mm Hg (p = 0.004) after 11(2) minutes, indicating an acute reduction in arterial resistance. Gallopamil did not significantly change mean heart rate or blood pressure. In the sitting position three hours after administration gallopamil and metoprolol significantly lowered power spectral density in the low frequency band (0.03 Hz to 0.15 Hz) compared with placebo (p < 0.05). Nifedipine did not produce such an effect. CONCLUSIONS: Gallopamil and metoprolol both inhibit cardiac sympathetic activation compared with placebo, whereas nifedipine causes reflex sympathetic activation.

Adult↗
PubMed1991

Ventricular late potentials in patients with and without inducible sustained ventricular tachycardia: a combined analysis in the time and frequency domain.

Time and frequency of signal-averaged electrocardiograms from 51 patients and 19 normal subjects were studied. A new filter device was designed to facilitate the analysis of the complete QRS complex, particularly the high-frequency components. All patients underwent electrical programmed stimulation (EPS) with up to three extra stimuli. In 29 patients, sustained ventricular tachycardia (VT) was inducible (group A), whereas in 22, sustained VT could not be elicited (group B). Between A and B, we compared several variables from the signal-averaged ECG as well as clinical data. The variables that differed between the two groups (P less than 0.01) were entered into a logistic regression model to determine which ones could most reliably predict the outcome of EPS. A combination of three variables (number of minima and maxima in the terminal QRS; third of four areas of equal length, divided by the total area below the QRS; maximum of the frequency spectre in the terminal QRS) could predict the inducibility of sustained VT with 82.8% sensitivity and 86.4% specificity.

Adult↗