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J Hennig

Publications and source records attributed to J Hennig.

At least 19 recordsLinked to original sources
PubMed1997

Time-resolved projection angiography after bolus injection of contrast agent.

A method for MR angiography after bolus injection of a normal dose (0.1 mmol/kg) of contrast agent is presented. Projection angiograms are acquired with a non-slice selective Snapshot FLASH sequence with a time resolution of 1 s per image or better. Typically 40 to 60 images are acquired consecutively after bolus injection of a contrast agent. The signal from vessels can be separated from background by postprocessing based on the observed temporal evolution of the signal intensities during bolus passage. The subsecond projection MR-DSA is a reliable and robust technique to produce high resolution anatomical images of the vascular system avoiding the necessity of exact timing of the contrast agent bolus. It also supplies functional information about the hemodynamics in the observed region including perfusion.

Contrast Media↗
PubMed1997

Improved sensitivity to overlapping multiplet signals in in vivo proton spectroscopy using a multiecho volume selective (CPRESS) experiment.

A method for volume selective proton spectroscopy is presented based on a multiecho sequence with short refocusing interval tcp. It is demonstrated, that by appropriate choice of tcp on the order of 4-6 ms, signals from overlapping multiplets like the glutamine and glutamate (Glu/Gln) resonances in spectra of the human brain are considerably increased compared with a conventional PRESS volume selection scheme. Thus proton spectra from J-coupled multiplet signals can be acquired with TE on the order of 20-30 ms avoiding the baseline problems arising at shorter echo times due to broad resonances. This allows to selectively acquire spectra from substances with longer T2 without the confounding effects from J-coupling occurring in conventional volume selection techniques.

Alanine↗
PubMed1997

Proton magnetic resonance spectroscopy of the brain in symptomatic and asymptomatic patients with liver cirrhosis.

BACKGROUND & AIMS: Hepatic encephalopathy (HE) is associated with typical changes of cerebral metabolite pattern observed by proton magnetic resonance (MR) spectroscopy consisting of a depletion of myo-inositol and an increase of glutamine. The aim of this study was to determine whether abnormalities in brain metabolism in neurologically asymptomatic patients with liver cirrhosis can be detected by spectroscopy. METHODS: In a prospective study, 39 patients with liver cirrhosis were examined clinically according to standardized neuropsychological tests to define whether overt, subclinical, or no hepatic encephalopathy was present. All patients underwent proton MR spectroscopy at short echo times. RESULTS: Spectroscopy allowed for the diagnosis of subclinical HE in 4 of 4 cases and of overt HE in 10 of 11 cases. In 24 cases of mere liver cirrhosis and normal neuropsychological testing, a typical metabolic pattern with a depletion of myo-inositol and an increased glutamine peak were found. A good correlation between the glutamine signal and the clinical grading was found. CONCLUSIONS: Proton MR spectroscopy allows for the diagnosis of HE and subclinical HE, also shows the typical pathological metabolite pattern in patients with cirrhotic livers without subclinical HE, and might be more sensitive than neuropsychological testing. Glutamine could serve as a spectroscopic marker for the clinical state of the patients.

Aged↗
PubMed1996

Implementation of a fast gradient-echo SVD encoding technique for dynamic imaging.

In the paper, the results of a fast gradient-echo implementation of the singular value decomposition (SVD) encoding technique for dynamic imaging are presented. The method used is an adaptation with several critical modifications of a keyholetype approach previously proposed but not implemented. The method was tested by imaging the events following injection of a contrast agent into a phantom, producing a series of dynamic image updates. It is demonstrated that, for this type of application, the SVD encoding technique adequately follows dynamic changes with even a small number of encodes. The result is compared qualitatively to that obtained by standard Fourier-based keyhole imaging and is shown to provide improved spatial resolution of dynamic events when updating with the same number of encodes.

Algorithms↗
PubMed1996

Frequency resolved single-shot MR imaging using stochastic k-space trajectories.

A new single-shot stochastic imaging technique with a random k-space path that provides very selective filtering with respect to chemical shift or off-resonance signals of the investigated tissue is proposed. It is demonstrated that in stochastic imaging only on-resonance compartments are visible whereas frequency shifted compartments cancel to noise that is distributed over the whole image. This method can be used as a single-shot chemical shift selective imaging technique and allows to calculate frequency resolved spectra for each spatial position of the image based on a single signal acquisition. The single-shot stochastic imaging sequence makes high demands on the gradient system and the theoretical k-space trajectory is distorted by imperfect gradient performance. Therefore an additional k-space guided imaging technique that uses the true, measured k-space trajectory to correct artifacts generated by eddy currents and delay times of the rapid switched gradients is presented. In vitro and in vivo measurements demonstrate the successful implementation of single-shot stochastic imaging on a conventional MR scanner with unshielded gradient systems.

Artifacts↗
PubMed1996

Multislice interleaved excitation cycles (MUSIC): an efficient gradient-echo technique for functional MRI.

A method providing improved slice efficiency for gradient-echo imaging requiring long echo times, such as in functional neuromagnetic resonance imaging, is presented. To enhance the volume coverage while maintaining the short imaging time of a conventional single-slice gradient-echo technique, an interleaved multislice excitation is performed during the echo time. This technique allows detection of susceptibility changes, e.g., the acquisition of stimulated human cortical activation maps, on clinical MR instruments at multiple planes within total imaging times of a few seconds. The efficiency of the technique is demonstrated in the detection of temporary changes in T2* in functional MRI experiments of the human visual cortex at magnetic field strengths of 2 Tesla and 3 Tesla. Fourteen 128 x 128 slices can be acquired in 13 s to cover a large volume-of-interest in the same time that would be required for single-slice acquisition using the conventional technique.

Adult↗
PubMed1996

5-HT agonist-induced changes in peripheral immune cells in healthy volunteers: the impact of personality.

The present study was conducted to investigate the relationship between the serotonergic neurotransmitter system and migration patterns of peripheral lymphocytes. Altogether 40 healthy male volunteers were given either a single dosage of the 5-HT1a-receptor agonist ipsapirone (10 mg) or a placebo (n = 20 each) in a double-blind randomized trial. Blood samples were drawn 55, 90 and 110 min after drug intake (baseline) and were analyzed for the number of peripheral lymphocytes. Furthermore, saliva samples were obtained at 13 defined time points which were analyzed for cortisol concentrations. Personality traits impulsivity, psychoticism and boredom susceptibility) were measured by questionnaires to investigate personality related differences in levels of serotonergic responsiveness. Analyses of covariance indicated that ipsapirone leads to highly significant reductions of peripheral CD4+ cells (T-helper/inducer-cells). This was significantly correlated to the ipsapirone-induced release of cortisol in a time-dependent manner. Furthermore, subjects scoring high on impulsivity, psychoticism and boredom susceptibility could be identified as being more responsive to the 5-HT agonist, indicated by their larger reduction in T-helper cells and greater cortisol release. This was hypothesized to be either due to their subsensitivity of presynaptic or supersensitivity of postsynaptic 5-HT1a-receptors.

Adult↗
PubMed1996

Local immunocompetence and salivary cortisol in confinement.

The present study describes the effects of a 60-day isolation period on the salivary levels of cortisol and secretory IgA. The study took place in the context of the EXEMSI project in which four volunteers were isolated in a space station-like chamber in the DLR Institute of Aerospace Medicine in order to examine the effects of long term isolation. Inspection of the individual immunoglobulin A secretion rates revealed different patterns of cyclic variation with respect to the weekday-weekend schedule, and different time lags for the adaptation leading to a plateau for this parameter. The salivary cortisol levels showed a circadian rhythm with high concentrations in the early morning (7:30 am) and lower concentrations in the late evening (11:00 pm). Moreover, in all subjects marked increases of salivary cortisol were observed in a 12- to 14-day cycle. In two subjects the marked morning-evening differences were only visible at the weekends. The salivary cortisol and immunoglobulin A levels were determined twice weekly before and after completion of a complex decision-making test. The results reveal a changed responsiveness in all subjects at different times.

Adult↗
PubMed1996

HIV-related metabolic abnormalities in the brain: depiction with proton MR spectroscopy with short echo times.

PURPOSE: To analyze brain metabolite changes in human immunodeficiency virus (HIV)-positive neurologically asymptomatic patients and patients with acquired immunodeficiency syndrome (AIDS) dementia complex (ADC). MATERIALS AND METHODS: Twelve ADC patients, 11 HIV-positive asymptomatic patients, and 10 healthy control subjects underwent magnetic resonance (MR) imaging and proton MR spectroscopy with short echo times. Changes in N-acetyl aspartate (NAA), choline (Cho), myoinositol (MI), and creatine (Cr) were presented as ratios with Cr as the reference. RESULTS: Statistically significant (P < .05) differences were noted. In ADC patients, all with MR findings of brain atrophy and diffuse white matter disease, NA/Cr decreased (white matter, -31.8%; gray matter, -22.3%), MI/Cr increased (white matter, +42.5%; gray matter, +51.8%), and Cho/Cr increased (white matter, +20.6%; gray matter, +51.7%) compared with healthy control subjects. In HIV-positive asymptomatic patients, NA/Cr decreased slightly (white matter, -6.9%; gray matter, -5.1%), MI/Cr increased slightly (white matter, +13.7%; gray matter, +10.7%), and Cho/Cr did not change. CONCLUSION: ADC has a uniform pathologic metabolic pattern that affects NAA, MI, and Cho. Proton MR spectroscopy with short echo times helps detect early abnormalities in clinically asymptomatic patients.

AIDS Dementia Complex↗
PubMed1996

Serotonin and dopamine as mediators of sensation seeking behavior.

The purpose of the present paper was to investigate the relationship of the serotonergic and dopaminergic systems to subscales of sensation seeking (SS). Two of the subscales, Disinhibition (DIS) and Experience Seeking (ES), were chosen for analysis based on their representation of the two major factors obtained in a factor analysis: DIS represents a factor of lack of impulse control and ES a factor of novelty seeking. In studies 1 and 2 responsivity to a serotonergic (5-HT) challenge by a 5-HT1a receptor agonist (ipsapirone) was investigated by drug-induced prolactin (PRL) and cortisol responses, as well as by emotional states and behavioral measures. The dopaminergic (DA) response to a DA agonist (lisuride) and antagonist (fluphenazine) was analyzed in a condition of smoking deprivation (study 3) using PRL responses, emotional states, and behavioral measures of nicotine craving as dependent variables. In the studies of the serotonergic system, high ES subjects showed a blunted cortisol response in both studies and high DIS subjects demonstrated a blunted PRL response in study 2. A frequently observed side effect of serotonergic agonists, increase in emotional arousal, was not observable with ipsapirone in high ES and high DIS subjects as compared to low scorers. Behavioral aggression, which had been experimentally induced in study 2, was increased in high ES as well as in high DIS by the 5-HT1a agonist which exerted antiaggressive effects in low scorers. These findings were found compatible with the idea of a generally low responsivity of the serotonergic system in high ES as well as in high DIS types of sensation seekers of 5-HT1a subsensitivity in high DIS and subsensitivity of other postsynaptic 5-HT receptors in high ES. There was no association between SS subscales and DA-induced decrease of PRL, but high ES subjects seemed to tolerate nicotine deprivation better than low ES subjects indicating that they were less susceptible to deprivation of nicotine-induced DA. But craving for nicotine was increased in high ES subjects by the DA agonist lisuride as opposed to the antagonist, which was taken as evidence that DA stimulation may induce approach behavior in high ES. Although only two subscales had been selected for the investigation, this approach suggests both common and different relationships between SS subscales and neurotransmitter systems.

Adult↗
PubMed1995

Breath-hold projection magnetic resonance-cholangio-pancreaticography (MRCP): a new method for the examination of the bile and pancreatic ducts.

Breath-hold MR cholangio-pancreaticography using the RARE method was evaluated as a noninvasive alternative to direct cholangio-pancreaticography in 30 healthy volunteers and in 30 patients with various diseases of the respective duct systems. In contrast to 3D MR cholangiography, RARE MRCP generates projection images requiring a 4-s acquisition time and no postprocessing. Diagnostic information gained from the cholangio-pancreaticograms was fully equivalent to that of conventional x-ray imaging by invasive procedures. Additional information was gained whenever endoscopic access was impossible and/or cystic malformations were present.

Adult↗
PubMed1995

Suppression of HPA-axis activity by haloperidol after experimentally induced heat stress.

1. Healthy male volunteers were exposed to either a heat condition (52 degrees C) or normal temperature (28 degrees C) receiving a single oral dose of 3 mg haloperidol or placebo in a double-blind design. 2. Ratings on aversiveness as well as on intensity of ambient temperature and saliva samples for determination of cortisol were sampled at defined intervals. Body core temperature and sweat loss were measured continuously throughout the three hour experiment. 3. Results indicate increased levels of cortisol after exposure to heat but not after a pretreatment with haloperidol. 4. The findings of this study suggest that D2-receptors of tuberoinfundibular neurons are blocked by haloperidol which suppresses the dopamine mediated release of vasopressin induced by dehydration and the subsequent stimulation of CRH.

Adult↗
PubMed1995

Quality assessment in in vivo NMR spectroscopy: IV. A multicentre trial of test objects and protocols for performance assessment in clinical NMR spectroscopy.

A multicentre trial of test objects and protocols for performance assessment in single volume and slice selective magnetic resonance spectroscopy (MRS) was conducted by the European Community Concerted Action on MRI and MRS. The trial assessed phosphorus and proton localisation techniques implemented on commercially available MR systems at ten sites in Europe. At each site, a number of parameters devised by the Concerted Action were measured using prototype test objects. Some of these parameters related to the quality of localisation and others to the overall performance of the spectrometer. Results were obtained for the ISIS, DRESS, STEAM, and PRESS sequences with a range of acquisition parameters, allowing evaluation of the assessment methodology and comparison of the efficacy of various implementations of these localisation techniques. The results of this trial have been important in the development of the Concerted Action's final recommendations for MRS performance assessment, and demonstrate that such assessment provides valuable information in the comparison of spectroscopy data from different sites and in the development of new localisation sequences, and provides a means of quality assurance in MRS.

Magnetic Resonance Spectroscopy↗
PubMed1995

Value of RARE-MRI sequences in the diagnosis of lymphangiomatosis in children.

Three patients suffering from extensive cavernous lymphangiomatosis are presented here. They were examined by MRI using RARE-MR hydrography (rapid acquisition with relaxation enhancement) as well as conventional spin-echo sequences. RARE sequences, which depict each fluid-filled lymphatic space, can be used for screening. RARE-sequences help to shorten investigation time, particularly in cases involving the skeleton. The imaging strategy can be changed according to the results of this sequence. It may be performed prior to spin-echo sequences and facilitates follow-up investigations. RARE sequences distinguish between lymphangiomatosis and hemangiomatosis, or a combination of the two.

Adult↗
PubMed1995

[Inversion recovery RARE: clinical use of a T2-weighted CSF-suppressed rapid sequence].

Inversion-Recovery RARE is a strongly T2-weighted fast sequence in which the CSF appears dark. This sequence was used in more than 100 patients. Retrospective analysis of 80 patients with cerebrovascular and inflammatory disease was carried out. The IR-RARE sequence proved to be particularly suitable for identifying small lesions in the neighbourhood of the subarachnoid space. We illustrate the typical contrast provided by this sequence, and describe its characteristics, exemplifying the advantages it offers for the diagnosis of multiple sclerosis, cerebral microangiopathy and brain infarction.

Adolescent↗