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Biomedical subjects

J Hennig

Publications and source records attributed to J Hennig.

At least 73 records · Page 4Linked to original sources
PubMed2000

Facilitation of electric forepaw stimulation-induced somatosensory activation in rats by additional acoustic stimulation: an fMRI investigation.

The influence of scanner acoustic noise on somatosensory activation pattern in rat cortex was investigated by functional magnetic resonance imaging (fMRI) using the blood oxygenation level-dependent (BOLD) contrast. This was achieved by two approaches. The first approach was to compare a conventional, loud fMRI sequence with a new sequence, in which the noise level was reduced by about 30 dB. In the second approach, the inner ear of the animal was destroyed, resulting in deafness. We compared the activation patterns obtained with both sequences before and after cochleotomy. The activated area was larger when data were sampled with background noise, and was also larger before cochleotomy than after. Thus, facilitation of somatosensory activation is induced by additional acoustic stimulation. Magn Reson Med 44:317-321, 2000.

Acoustic Stimulation↗
PubMed2000

Easy improvement of signal-to-noise in RARE-sequences with low refocusing flip angles. Rapid acquisition with relaxation enhancement.

It is demonstrated that the signal intensity in a RARE (TSE, FS...)-sequence with low refocusing flip angle alpha can be significantly increased by setting the flip angle of the first refocusing pulse to 90 degrees +alpha/2. In addition to the gain in signal intensity, the initial signal modulations over the first few echoes are reduced compared to a CPMG-echo train with constant alpha.

Artifacts↗
PubMed2000

Assessment of arterial blood flow characteristics in normal and atherosclerotic vessels with the fast Fourier flow method.

The purpose of this study was to scrutinize the ability of magnetic resonance imaging (MRI)-performed measurements to compare arterial flow patterns in patients with peripheral arterial occlusive disease (PAOD), healthy volunteers (HV) and endurance athletes (EA). MRI blood flow data were partially repeated with Doppler ultrasound (DUS) with a view to a methodical comparison. Additionally, pulse wave velocity was assessed with the MUFF technique. For this purpose, MRI-performed flow measurements were performed in the common femoral artery in 21 patients with PAOD, in 34 HV and in 12 EA. The analysis included maximum flow velocities (MFV), velocity/time profile (VTP), pulse wave velocity (Vpulse), and vessel diameter (VD). In addition, MFV and VD were observed by DUS in most individuals. The results revealed a significant change regarding arterial blood flow characteristics in patients compared with HV and EA, with respect to the span between the peak positive and negative blood flow velocity in the femoral artery. The pulse wave velocity in patients was markedly elevated compared with healthy individuals. Furthermore, a complete, characteristic change in the VTP could be observed in patients. The methodical comparison between DUS and MRI showed a good correlation. Multi-slice Fourier flow data have indicated markedly increased pulse wave velocity in PAOD patients. Changes in the arterial blood flow can be clearly observed with MRI. In the future, this might offer a noninvasive possibility not only for the evaluation of the stage of the disease, but also for the detection of early, pre-clinical stages of atherosclerosis.

Adult↗
PubMed2000

Functional MRA.

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Brain↗
PubMed2000

White blood cells and cortisol after sleep deprivation and recovery sleep in humans.

Sleep deprivation (SD) has enriched our treatment programme for major depression. SD has been demonstrated to modify different host defence activities. There is some evidence that there are reciprocal relationships between immune function and increased hypothalamic-pituitary-adrenocortical (HPA) axis activity in depression. We therefore investigated the number of leukocytes, granulocytes, monocytes, lymphocytes, B cells, T cells, helper T cells, cytotoxic T cells, NK cells and salivary cortisol 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 am, 1 pm and 7 pm, respectively. Comparison of the 7 am values by contrast analysis yielded significant differences for granulocytes (p = 0.044) and NK cells (p = 0.001) after SD and recovery sleep. NK cells decreased and granulocytes increased after SD and after recovery sleep. Significant differences between single points in time across the day were found for granulocytes (p = 0.022), monocytes (p = 0.031), T cells (p = 0.005), helper T cells (p = 0.004), cytotoxic T cells (p = 0.005) and NK cells (p = 0.017). No significant difference could be detected for leukocytes, lymphocytes and B cells counts. These results favour the thesis that SD and recovery sleep lead to changes in the distribution of peripheral leukocytes, especially in a reduction of NK cells after SD and recovery sleep. The cortisol rhythm was affected neither by SD nor recovery sleep.

Adult↗
PubMed2000

Time-resolved projection MRA: clinical application in intracranial vascular malformations.

We report preliminary results of imaging intracranial vascular malformations with time-resolved projection MRA after a bolus injection of contrast median before and after endovascular treatment. Projection angiograms are acquired with a slice-selective snapshot FLASH sequence with a time resolution of two images per second, 40-60 images being acquired consecutively after bolus injection of 15 ml Gd-DTPA. Postprocessing of images in 2D projection MRA by correlation analysis offers several advantages with significant improvement of signal-to-noise, leading to adequate anatomical resolution. Subsecond projection MRA is a reliable technique for imaging intracranial vessels and gives information about the haemodynamics of vascular malformations.

Angiography, Digital Subtraction↗
PubMed2000

Mechanisms of changes in lymphocyte numbers after psychological stress.

In the field of psychoneuroimmunology it has become obvious that the immune system is governed by multiple influences from the central nervous system. One approach to verify these interactions can be seen in stress research. While the phenomenon of stress-induced changes in immunological processes is widely accepted, more recent studies focus on possible moderators and mechanisms of these responses. Within this research strategy it became evident that catecholamine increases upon stress are of major importance for the frequently observed mild leukocytosis. The present study was conducted to investigate whether the often observed stress-induced increases in the number of peripheral lymphocyte subsets depends on the amount of epinephrine or norepinephrine release. Moreover, the question was addressed whether high or low catecholamine release is related to subjective ratings on discomfort. Using a "public speaking paradigm", we were able to replicate previous findings of high increases in the absolute number of CD8+ and CD56+ cells in peripheral blood. Moreover, when dividing subjects into high and low catecholamine responders, the amount of change was significantly larger in catecholamine responders irrespective of whether norepinephrine or epinephrine was used for grouping the subjects. However, high and low catecholamine responders did not differ with respect to subjective ratings on discomfort. The data are discussed with respect to underlying mechanisms in catecholamine-induced lymphocyte migration and possible reasons for the mismatch between objective and subjective indicators of stressor efficacy.

Adult↗
PubMed2000

Upright posture influences salivary cortisol.

This study was designed to investigate the influence of posture on salivary cortisol concentrations in healthy volunteers. In a balanced cross-over design 24 subjects were exposed at 1 week intervals to different body positions (sitting [S], lying [L] upright [U]) for 20 min in each condition. Before, during and after the experimental treatment measures of blood pressure, heart rate and saliva samples for determining the free fraction of cortisol were obtained. Furthermore, at corresponding time points a questionnaire on emotional states was completed. In addition, subjects were requested to complete personality questionnaires before the experiment and to rate their emotional states during saliva sampling. Results clearly indicate that the circadian decrease of cortisol concentrations was present only in the conditions [S] and [L] whereas in [U] salivary cortisol concentrations increased significantly. As expected, heart rate accelerations associated with a marked reduction of systolic blood pressure were observed in [U]. To further examine the relationship between hormonal and cardiovascular responses as indicators of autonomic activation, correlations between change scores were computed indicating that a relationship between cardiovascular responses and cortisol increases is not restricted to [U]. Positive correlations were observed between changes in systolic blood pressure and changes in cortisol concentrations in both conditions [U] and [L]. Posture does not affect emotional states indicating independence between posture induced physiological responses and experienced discomfort. Posture therefore should be adequately controlled, since those non-specific increases of hormones may interfere with state or trait dependent responses. Data are discussed with respect to the importance to control for posture in field and experimental studies and to possible mechanisms of posture induced changes in cortisol.

Anxiety↗
PubMed2000

Thermosensitive paramagnetic liposomes for temperature control during MR imaging-guided hyperthermia: in vitro feasibility studies.

RATIONALE AND OBJECTIVES: Magnetic resonance (MR) imaging-based temperature monitoring has gained interest for use in general hyperthermia treatment of tumors. Such therapy requires an accurate control of the temperature, which should range from 41 degrees to 45 degrees C. A novel type of thermosensitive MR agent is proposed: liposome-encapsulated gadolinium chelates whose temperature response is linked to the phase-transition properties of the liposome carrier. In vitro relaxometry and MR imaging were used to evaluate the thermosensitivity of the contrast properties of liposomal gadolinium diethylenetriaminepentaacetic acid bis(methylamide) (Gd-DTPA-BMA). MATERIALS AND METHODS: T1 relaxivity (rl) measurements of liposomal Gd-DTPA-BMA were undertaken at 0.47 T and at temperatures of 20 degrees-48 degrees C. MR imaging was performed at 2.0 T with a gel phantom containing inserts of liposomes. Diffusion-weighted and T1-weighted gradient-recalled echo images were acquired as the phantom was heated from 22 degrees to about 65 degrees C. RESULTS: At ambient temperature, the r1 of liposomal Gd-DTPA-BMA was exchange limited due to slow water exchange between the liposome interior and exterior. A sharp, marked increase in r1 occurred as the temperature reached and exceeded the gel-to-liquid crystalline phase-transition temperature (Tm) of the liposomes (42 degrees C). The relaxation enhancement was mainly attributable to the marked increase in transmembrane water permeability, yielding fast exchange conditions. There was good correlation between the relaxometric and imaging results; the signal intensity on T1-weighted gradient-recalled echo images increased markedly as the temperature approached Tm. The temperature sensitivity of the diffusion-weighted technique differed from that of the liposome-based T1-weighted approach, with an apparent water diffusion coefficient increasing linearly with temperature. CONCLUSION: Since the transition from low to high signal intensity occurred in the temperature range of 38 degrees - 42 degrees C, the investigated paramagnetic liposomes have a potential role as "off-on" switches for temperature control during hyperthermia treatment.

Contrast Media↗
PubMed2000

Extracellular glutamate and other metabolites in and around RG2 rat glioma: an intracerebral microdialysis study.

The current study determined the extracellular content of glutamate, 10 additional amino acids, lactate, glucose and some antioxidants in a rodent model of malignant glioma, its peritumoral space and the adjacent cortex. RG2 tumors were induced in the right frontal cortex of Fischer-344 rats (n = 10) by a standardized procedure to obtain a maximum sagittal tumor width of 3-4 mm diameter. After confirmation of tumor growth and localization by contrast enhanced MRI three microdialysis probes were implanted simultaneously in the cortex: at the tumor implantation site (tumor), 2 mm caudally, brain around tumor (BAT) and 4 mm caudally (cortex) to the site of implantation. Dialysate concentrations of glutamate were increased 3.9-fold in tumor and 2-fold in BAT compared with cortex. Glycine was elevated 11.4-fold in tumor and 2.6-fold in BAT. Lactate was increased 1.7-fold in tumor, 1.2-fold in BAT. Levels of glucose, ascorbic acid and uric acid were not significantly different in tumor, BAT and cortex. The increased dialysate levels of glutamate and glycine in the peritumoral space may contribute to impaired neuronal function and epileptiform activity associated with this tumor type in humans.

Amino Acids↗
PubMed2000

Endocrine responses after d-fenfluramine and ipsapirone challenge: further support for Cloninger's tridimensional model of personality.

The tridemensional model of personality introduced by Cloninger relates aspects of novelty seeking to the dopaminergic, harm avoidance (HA) to the serotonergic, and reward dependence to the noradrenergic neurotransmitter system. Using a neuroendocrine challenge paradigm, this study investigates whether subjects characterized by blunted cortisol (CORT) responses after ipsapirone (IPS) relate to different subfactors of HA from those characterized by blunted prolactin (PRL) responses after treatment with d-fenfluramine (D-FEN). Moreover, subjects blunted in both responses should differ in scale values of subfactors of HA from those with only one or no blunted reactions. In the first part of the experiment, 16 healthy male volunteers were treated with 15 mg D-FEN. The second part of the study (about 1 year later) consists of a challenge with the partial 5-hydroxytryptamine-1a (5-HT(1a)) agonist IPS (10 mg) in the same subjects. The results indicate that blunted PRL responses are accompanied by high values in HA, while the main effect of IPS responsivity did not relate significantly to this dimension. With respect to the subscales of HA, subjects blunted in both responses (PRL-/C-) exhibit significantly higher levels in fatigability and asthenia when compared to all other groups (PRL-/C+, PRL+/C-,PRL+/C+). The data demonstrate that combined challenge tests may shed more light on the biological basis of personality and that HA and most clearly fatigability and asthenia relate to the 5-HT system.

Adult↗
PubMed1999

Spiral reconstruction by regridding to a large rectilinear matrix: a practical solution for routine systems.

Spiral trajectories offer a number of attractive features for fast imaging. A practical problem for the implementation on routine magnetic resonance scanners is the lack of appropriate and efficient reconstruction algorithms in the available scanner software. In this paper, a simple way to implement a spiral reconstruction algorithm is described that avoids the data interpolation required by gridding approaches commonly used. Using the optimized fast Fourier transform built into each scanner, it offers image reconstruction times of less than 1 second and thus allows the introduction of spiral imaging to routine scanners.

Algorithms↗
PubMed1999

Neural network-based analysis of MR time series.

Clustering has been introduced to analyze fMRI data by means of partitioning data into time series of similar temporal behavior. It is hoped that one of these clusters represents a dynamic effect of interest, like functional activation. Using self-organizing maps for clustering, additional information can be obtained by ordering cluster centers on a two-dimensional projection plane. The map's capability of data visualization is used to summarize all dynamic effects of an experiment by means of data partitioning. The map does allow differently sized and populated clusters in the data by forming "superclusters" on the map. The method is introduced as a conceptual extension to clustering. Applications to fMRI and to MR mammography are discussed.

Artifacts↗
PubMed1999

K-space sampling strategies.

The k-space algorithm offers a comprehensive way for classification and understanding of the imaging properties of all commonly used MR sequences. This presentation describes the basic concepts of k-space and its most relevant properties for MR imaging. The ramifications of k-space sampling is discussed for the most commonly used groups of MR sequences including gradient-echo techniques, echo-planar imaging, spin echo, and rapid acquisition relation enhanced imaging (e. g., turbo spin echo, fast spin echo). In addition, the basic problems and properties of sequences based on non-rectilinear k-space sampling, such as spiral imaging, are discussed. Their artifact behavior is significantly different from rectilinear scans, which project all imperfections along the phase-encoding directions, whereas the artifact produced by spirals are more complex and not always easily recognizable as such. An understanding of the k-space sampling offers important insight into the basic properties of a given sequence regarding signal-to-noise ratio, image distortion, resolution and contrast. It is demonstrated that the ultimate limitation in imaging speed is given by the loss of signal-to-noise ratio inherent to faster data sampling.

Algorithms↗
PubMed1999

Changing psychobiological stress reactions by manipulating cognitive processes.

This study aimed at manipulating psychobiological reactions to public speaking stress by means of verbal comments during the anticipation period. Sixty male students were instructed to give a public talk in 10 min. Twenty subjects each were randomly assigned to one of three experimental conditions: During anticipation of the speech the experimenter remained silent in the control condition, gave feedback that the subject was physiologically aroused and nervous in the second (arousing manipulation), or that he was physiologically calm and relaxed in the third condition (reassuring manipulation). Within the three stress conditions heart rate, systolic blood pressure, cortisol, and electrodermal responses were highest in the condition with reassuring manipulation and lowest in the condition without manipulation. Emotional stress reactions were highest in the condition with arousing manipulation and lowest in the condition with reassuring manipulation. Compared to the group without manipulation clear intraindividual discrepancies between emotional and somatic stress reactions could be observed in the group with reassuring manipulation (emotional < somatic arousal) and the group with arousing manipulation (emotional > somatic arousal). The two groups were significantly different in their discrepancy scores. It was concluded that the arousing manipulation seemed to have induced a sensitive, the reassuring manipulation a defensive coping style.

Adolescent↗
PubMed1999

Cardiac phase contrast gradient echo MRI: measurement of myocardial wall motion in healthy volunteers and patients.

A number of methods have been proposed for the noninvasive measurement of myocardial wall motion. The paper describes a strategy for assessing myocardial motion based on the sensitivity of the phase of the MR-signal to motion using a breath-hold phase contrast technique. A motion-sensitized and a motion-compensated MR-signal are measured during successive scans. The difference between the two MR-signals is used to calculate myocardial velocity in all three spatial dimensions. Postprocessing includes the transformation of the measured velocities into an internal coordinate system of the left ventricle. Also various presentation modes and further processing of the received velocity information are provided including calculation of global motion parameters. We examined 20 patients suffering from myocardial infarction. The overall left ventricular motion can be characterized by appropriate parameters describing the rotation and contraction or expansion, respectively. Regional motional disturbances are visualized using parametric images. Contrary to the highly consistent interindividual data in normal volunteers, patients showed significant localized motion deficits.

Adult↗
PubMed1999

Psychobiological differences between the aggression and psychoticism dimension.

Since blunted prolactin (PRL) and partly blunted cortisol responses have been reported for subjects with aggressive impulsive disorders as well as with psychopathy, it seemed worthwhile to try to separate the two types of aggression by their biological response. Since, furthermore, cortisol responses are more readily elicited by 5-HT1a challenges and prolactin responses by d-Fenfluramine or uptake inhibitors, these two types of drugs were used to answer the question if these hormone responses are suitable to differentiate between the two types of aggression. Two studies were conducted, one using 15 mg of d-Fenfluramine (d-Fen) in a double-blind placebo-controlled cross-over design in 40 males, the other using 10 mg of Ipsapirone (Ips) and placebo comparing 20 healthy males in each group. In each study subjects were divided according to above and below median aggression and psychoticism scores measured by questionnaire scales and combined into four groups defined by high and low aggression (Ag+/-) and psychoticism (P+/-) scores respectively. Analyses of covariance based an the two personality factors and the drug revealed for d-Fen cortisol nonresponse in P+ as opposed to P- and a blunted PRL response in Ag+ as opposed to Ag-. With Ips the cortisol response was positively related to Ag and not to P, while P+ showed a blunted PRL response not observed in Ag+. Joyfulness and well-being were also differentially affected by d-Fen in high and low P scorers, but not correlated to respective hormone responses. Different hypothalamic mechanism for eliciting the two hormone responses and differences in pre- and postsynaptic receptor sensitivities in the two personality dimensions are inferred from these findings.

Adult↗