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Biomedical subjects

B Pfeifer

Publications and source records attributed to B Pfeifer.

At least 19 recordsLinked to original sources
PubMed2007

AAM-based segmentation for imaging cardiac electrophysiology.

OBJECTIVES: Activation time (AT) imaging from electrocardiographic (ECG) mapping data has been developing for several years. By coupling 4-dimensional volume data (3D + time) the electrical sequence can be computed non-invasively. In this paper an approach for extracting the ventricular and atrial blood masses for structurally normal hearts by using cine-gated short-axis data obtained via magnetic resonance imaging (MRI) is introduced. METHODS: The blood masses are extracted by employing Active Appearance Models (AAMs). The ventricular blood masses are segmented, applying the AAMs after providing apex cordis and base of the heart in the volume data, whereas the more complex geometry of the atria requires a more specific attempt. On account of this the atrium was divided into three divisions of appearance, where the images of the volume data in the related divisions have a maximum affinity. The first division reaches from the base of the heart to initial visibility of the upper and left lower pulmonary vein. The second division up from there to the last occurrence and the third division from there to the end of the visibility of the right upper and lower pulmonary vein. After extracting the cardiac blood masses the result gets triangulated and remeshed for activation time imaging. RESULTS: With this method the cardiac models of eight patients were extracted and the AT imaging approach was applied to single-beat ECG data of atrial and ventricular depolarization. CONCLUSION: The advantage of the proposed AAM approach is that only a few initial parameters have to be set. Therefore, the approach can be integrated into a processing pipeline that works semi-automatically. The extracted models can be used for further investigations.

Atrial Function↗
PubMed2006

[Patient acceptance of magnetic resonance colonography: a prospective inquiry for comparison to conventional colonoscopy].

BACKGROUND AND OBJECTIVE: Precondition for establishment of magnetic resonance colonography (MRCG) as a diagnostic tool in secondary prevention of colorectal cancer is not only high diagnostic accuracy but also a good acceptance amongst patients. The aim of this study was to compare post-examination appraisal of patients for MRCG to that of bowel preparation and conventional colonoscopy. PATIENTS AND METHODS: 88 patients (24 women, 64 men, mean age 67 +- 17,3 years) were interviewed by a standardized questionnaire regarding pain/discomfort (scale from 1 to 10), overall assessment of difficulties and preference for future tests. After bowel cleansing, MRCG and conventional colonoscopy were performed on the same day. Bowel cleansing consisted of drinking about 5 liters of a polyethylene glycol-electrolyte solution. For MRCG the colon was filled with ca. 2000 ml of tap water. Imaging was performed with a 1.5T MR scanner in the prone position. RESULTS: Most unpleasant for the patients was the preceding bowel preparation (70%), followed by colonoscopy (14%) and MRCG (8%). The preferred method was MRCG (58%) followed by colonoscopy (20,5%). The most unpleasant symptoms named by patients were the amount of oral electrolyte solution that had to be drunk (34%), abdominal pressure (25%), nausea (24%) because of bowel preparation, body positioning (25%) and rectal tube (13%) during MRCG, abdominal pressure (19%) and pain (18%) during colonoscopy. CONCLUSION: Patients' acceptance of MRCG indicates that it has a potential role as an additional diagnostic tool in secondary prevention of colorectal cancer.

Aged↗
PubMed2006

Atrial and ventricular myocardium extraction using model-based techniques.

OBJECTIVES: This paper presents an efficient approach for extracting myocardial structures from given atrial and ventricular blood masses to enable non-invasive estimation of electrical excitation in human atria and ventricles. METHODS: Based on given segmented atrial and ventricular blood masses, the approach constructs the myocardial structure directly, in the case that the myocardium can be detected in the volume data, or by using mean model information, in the case that the myocardium cannot be seen in the volume data due to image modalities or artefacts. The approach employs mathematical and gray-value morphology operations. Regulated by the spatial visibility of the myocardial structure in the medical image data especially the atrial myocardium needs to be estimated repeatedly using the a-priori knowledge given by the anatomy. RESULTS: The approach was tested using eight patient data sets. The reconstruction process yielded satisfying results with respect to an efficient generation of a volume conductor model which is essential when trying to implement the estimation of electrical excitation in clinical application. CONCLUSION: The approach yields ventricular and atrial models that qualify for cardiac source imaging in a clinical setting.

Algorithms↗
PubMed2005

The challenge of ubiquitous computing in health care: technology, concepts and solutions. Findings from the IMIA Yearbook of Medical Informatics 2005.

OBJECTIVES: To review recent research efforts in the field of ubiquitous computing in health care. To identify current research trends and further challenges for medical informatics. METHODS: Analysis of the contents of the Yearbook on Medical Informatics 2005 of the International Medical Informatics Association (IMIA). RESULTS: The Yearbook of Medical Informatics 2005 includes 34 original papers selected from 22 peer-reviewed scientific journals related to several distinct research areas: health and clinical management, patient records, health information systems, medical signal processing and biomedical imaging, decision support, knowledge representation and management, education and consumer informatics as well as bioinformatics. A special section on ubiquitous health care systems is devoted to recent developments in the application of ubiquitous computing in health care. Besides additional synoptical reviews of each of the sections the Yearbook includes invited reviews concerning E-Health strategies, primary care informatics and wearable healthcare. CONCLUSIONS: Several publications demonstrate the potential of ubiquitous computing to enhance effectiveness of health services delivery and organization. But ubiquitous computing is also a societal challenge, caused by the surrounding but unobtrusive character of this technology. Contributions from nearly all of the established sub-disciplines of medical informatics are demanded to turn the visions of this promising new research field into reality.

Biomedical Technology↗
PubMed2005

A signal processing pipeline for noninvasive imaging of ventricular preexcitation.

OBJECTIVES: Noninvasive imaging of the cardiac activation sequence in humans could guide interventional curative treatment of cardiac arrhythmias by catheter ablation. Highly automated signal processing tools are desirable for clinical acceptance. The developed signal processing pipeline reduces user interactions to a minimum, which eases the operation by the staff in the catheter laboratory and increases the reproducibility of the results. METHODS: A previously described R-peak detector was modified for automatic detection of all possible targets (beats) using the information of all leads in the ECG map. A direct method was applied for signal classification. The algorithm was tuned for distinguishing beats with an adenosine induced AV-nodal block from baseline morphology in Wolff-Parkinson-White (WPW) patients. Furthermore, an automatic identification of the QRS-interval borders was implemented. RESULTS: The software was tested with data from eight patients having overt ventricular preexcitation. The R-peak detector captured all QRS-complexes with no false positive detection. The automatic classification was verified by demonstrating adenosine-induced prolongation of ventricular activation with statistical significance (p <0.001) in all patients. This also demonstrates the performance of the automatic detection of QRS-interval borders. Furthermore, all ectopic or paced beats were automatically separated from sinus rhythm. Computed activation maps are shown for one patient localizing the accessory pathway with an accuracy of 1 cm. CONCLUSIONS: The implemented signal processing pipeline is a powerful tool for selecting target beats for noninvasive activation imaging in WPW patients. It robustly identifies and classifies beats. The small beat to beat variations in the automatic QRS-interval detection indicate accurate identification of the time window of interest.

Action Potentials↗
PubMed2005

Computationally efficient noninvasive cardiac activation time imaging.

OBJECTIVE: The computer model-based computation of the cardiac activation sequence in humans has been recently subject of successful clinical validation. This method is of potential interest for guiding ablation therapy of arrhythmogenic substrates. However, computation times of almost an hour are unattractive in a clinical setting. Thus, the objective is the development of a method which performs the computation in a few minutes run time. METHODS: The computationally most expensive part is the product of the lead field matrix with a matrix containing the source pattern on the cardiac surface. The particular biophysical properties of both matrices are used for speeding up this operation by more than an order of magnitude. A conjugate gradient optimizer was developed using C++ for computing the activation map. RESULTS: The software was tested on synthetic and clinical data. The increase in speed with respect to the previously used Fortran 77 implementation was a factor of 30 at a comparable quality of the results. As an additional finding the coupled regularization strategy, originally introduced for saving computation time, also reduced the sensitivity of the method to the choice of the regularization parameter. CONCLUSIONS: As it was shown for data from a WPWpatient the developed software can deliver diagnostically valuable information at a much shorter span of time than current clinical routine methods. Its main application could be the localization of focal arrhythmogenic substrates.

Arrhythmias, Cardiac↗
PubMed1991

Is a serotonergic mechanism involved in 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-induced appetite suppression in the Sprague-Dawley rat?

The major cause of TCDD-induced death in rats is a progressive voluntary feed refusal which has been correlated with reduced gluconeogenesis. Since centrally administered TCDD does not cause death or decreased feed intake in rats, the ability of TCDD to suppress appetite via peripheral mechanisms acting on the central nervous system was examined in two experimental models. First, it was found that the feed intake of rats on scheduled feeding cycles was not decreased by blood transfused from rats with TCDD-induced appetite suppression (8 days after a lethal dose of TCDD, i.p.). In contrast, a similar transfusion from normal, satiated rats did reduce feed intake of recipient rats by approximately 40%, suggesting that TCDD-treated rats are not satiated but rather that they are not hungry. In the second study tryptophan (the amino acid precursor of the neurotransmitter serotonin) was measured in the plasma and tryptophan, serotonin, norepinephrine and dopamine in the hypothalamus as well as dopamine and its metabolites in the striatum 4, 8, and 16 days after TCDD dosage (125 micrograms/kg, i.p.). Progressive time-dependent increases in tryptophan levels in plasma and brain were paralleled by increases in brain serotonin and 5-hydroxyindoleacetic acid (the primary metabolite of serotonin) in TCDD-treated rats. No changes were observed regarding the other biogenic amines. It is suggested based on these data and on substantial evidence from the published literature that a serotonergic mechanism may be involved in TCDD-induced feed intake reduction.

Animals↗
PubMed1990

Relationship between electrical and mechanical properties of motor units.

In six healthy volunteers, the size of the motor unit action potential (MUAP) was related to its contractile behaviour. Electrical activity was determined by measuring amplitude and area of the potential, using the macro electromyography (EMG) technique. The mechanical response was characterised by contraction time, twitch force and relaxation time, recorded with the spike triggered averaging technique. With increasing tension of the whole muscle corresponding to an increasing threshold, the force of single units enlarged exponentially compared to their EMG. There was only a weak relationship between contraction time and electrical activity and none between EMG and relaxation time.

Action Potentials↗
PubMed1990

[Methodology and diagnostic potentialities of macro-EMG. I. Methodology].

Macro-EMG records electrical activity from the whole motor unit (MU) as a parameter of its size. The main component of the recording device is a modified single fiber or concentric needle electrode. Different sized uptake areas allow to record with different selectivities from the MU. The teflon insulated shaft surface allows to record with a defined large blank area unselectively macro-signals from the muscle. The conceptual ideas to use a concentric needle in addition to the single fibre electrode is to simplify the trigger-potential recording, which needs to be selective within the MU. In both instances the EMG apparatus has to provide two channels, one for the trigger and the second for an averaging device to record the macro-EMG. The different techniques use the single fiber or concentric EMG-potential as a trigger to average the associated macro-potential from the raw signals. The electrodes different design allow the whole single-fiber-needle to lie within the MU territory whereas the MU is only touched by the concentric needles tip. This implies different recording situations and results. Anatomically macro-EMG size is varied by the recording site of the muscle. The signal is greater close to the endplate zone and declines to stable values about 20 mm apart. For quantitative measurements within a muscle 20 different potentials have to be evaluated for median amplitude, duration and area.

Electromyography↗
PubMed1990

[Methodology and diagnostic possibilities of macro-EMG. II. Diagnostic possibilities].

The macro-EMG can be recorded with a modified single fiber or concentric needle. The two needles attain different results with smaller potentials values for the concentric needle type. For the single fiber type normal data are given for the EDC and tibialis anterior muscle. These data are compared with previously published results and their statistical evaluation. The concentric needle type can be used for scanning EMG. In addition potential stability can be examined in different parts of the MU using the unblanketing principle. A further novel use for macro-EMG is simultaneous single motor unit twitch recording to compare mechanical and electrical MU activity. In normal muscle the electrical signal is positively correlated with twitch force. In diseased muscle like ALS twitch is dissociated from electrical potential size. Macro-EMG allows to quantify MU size, a prerequisite to follow up dynamic changes in muscle. Improved computer programs in commercially available EMG-machines will help to introduce this method into clinical EMG laboratories as a useful addition to increase the diagnostic yield of EMG.

Electromyography↗
PubMed1989

[Herpes zoster ophthalmicus with subsequent oculomotor paralysis and homolateral media infarct].

Oculomotor palsy is a well-known complication of herpes zoster ophthalmicus (HZO). Combination with homolateral cerebral media infarction and contralateral hemiplegia is very rare. Since the first paper on HZO and cerebral ischemia was published, in 1919, about 70 cases have been described. Zoster infection is thought to encroach from the fifth cranial nerve on to a cerebral artery at the base of the brain. The authors describe a case of HZO seen by them, with oculomotor palsy and ipsilateral media infarction with contralateral hemiplegia and aphasia. A review of the literature is given and etiologic and therapeutic aspects are discussed.

Aphasia↗
PubMed1988

[Macro-EMG: methodology and problems of determining normal values using the common extensor muscle of the fingers as an example].

The macro-EMG technique registers simultaneously two different potentials from one motor unit. One signal is a single fiber potential, the other an unselective compound recording (macro) of the action potentials of all the muscle fibers within this unit. So motor unit size can be quantified by its electrical activity. Measured data can only be judged upon if normal data are available. These we compiled for the extensor digitorum communis muscle in 83 healthy volunteers. As parameters of the macro-potential amplitude, area and duration were evaluated. It is shown, that amplitude and area are sufficient to characterise a potential. The potential itself is strongly influenced by age and muscle volume. Diagnostic evaluation of the macro-potential is only possible within the context of the results of the single fiber recording and the estimation of fiber density. We found within 105 normal persons a fiber density between 1.2 to 1.9 without a significant dependence on age. With our normal data it is now possible to derive diagnostic conclusions from macro-EMG data.

Adolescent↗
PubMed1986

The spontaneous burst activity of peripheral blood monocytes in patients with acute polyradiculoneuritis, lymphocytic meningoencephalitis, and multiple sclerosis. A comparison.

The course of the spontaneous burst activity (BA) of peripheral blood monocytes was examined in patients with acute polyradiculoneuritis (PN), lymphocytic meningoencephalitis (LE), and multiple sclerosis (MS) and the BA was compared with the clinical course. In 4 patients with postinfectious acute PN the BA was significantly increased up to values around 60 000 counts/10 s. The BA and the clinical course were closely correlated in these patients (mean of r = 0.83). In 4 patients with lymphocytic LE the BA initially was moderately increased to values between 4 000 and 5 000 counts/10 s and showed again a very close correlation with the clinical course (mean of r = 0.99). In 13 MS patients the BA values were found markedly increased showing a close correlation with clinical improvement (mean of r = -0.94) whereas in 2 patients without improvement the BA remained at low levels. The comparison of the clinical course with that of the BA in the three inflammatory diseases of the nervous system reveals that patients with PN and LE show high BA values whilst the clinical signs and symptoms are most expressed, whereas the BA is low in this phase of illness in MS patients but increases around the beginning of improvement. Possible meanings of this behaviour of the BA are discussed.

Acute Disease↗
PubMed1984

[Motor function loss in zoster neuritis versus encephalitis--clinical case and review of literature].

Motor lesions following herpes zoster are quite common. Hemiparesis, paraparesis, pareses of the facial and other cranial nerves as well as segmental pareses can be observed. We report on a patient suffering from zoster ophthalmicus complicated by paresis of the third cranial nerve. As a cause, a partial brain stem-encephalitis was diagnosed. The patient recovered after antiviral treatment (Aciclovir, Inosiplex).

Acyclovir↗
PubMed1984

[Polyradiculomeningoencephalitis caused by Epstein-Barr virus infection--description of a case with fatal outcome].

A 21 years old high school student, who, since early childhood, suffered from complete spinal paraplegia of unknown cause at D 10, suddenly, after a three week period with influenca -like prodromal symptoms, presented with acute polyradiculomeningoencephalitis . Positive reactions following Paul-Bunnell- Davidsohn -test and tests for specific antivirus IgG as well as specific IgM revealed acute Epstein-Barr-Virus infection, although no glandular signs could be found. The clinical findings consisted of peripheral sensory-motor tetraparesis, ataxia, nystagmus and disturbances of the caudal cranial nerves. Initially, the diagnosis of Fisher's syndrome was made. The orbicularis oculi reflex, however, indicated a circumscribed brainstem lesion in the medial reticular formation. This finding lead to the additional clinical diagnosis of encephalitis. Shortly after admission, a heart-arrest occurred, and, after successful reanimation, the patient presented with a "locked-in syndrome". On the 12th day after admission, he succumbed during a sudden drop of blood-pressure. Necropsy revealed septic shock as the cause of death, due to perforation of a duodenal ulcer. In the lower thoracic spinal cord a neurocytoma was found, which once lead to the paraplegia. Additionally, moderate inflammatory infiltrations were found in the basal leptomeninges, in the walls of several subcortical vessels and in the hypoglossal nerve. The infiltrations, at some sites, contained a large number of atypical lymphoid cells in the inflammatory meningeal exsudate . Microglial proliferation with satellitosis was found in the inferior olives, thus confirming the clinical diagnosis of polyradiculomeningoencephalitis . This case report should emphasize special features of EBV-infection with neurological complications: (1) in inflammatory diseases of the peripheral and central nervous system, infectious mononucleosis should always be drawn into the diagnostic considerations, even if heterophil antibodies and glandular symptoms are lacking. (2) In Guillain-Barré-syndrome, a transient external heart stimulator should be administered, in order to prevent heart arrest from acute autonomic neuropathy.

Adult↗