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Biomedical subjects

J Hennig

Publications and source records attributed to J Hennig.

At least 127 records · Page 7Linked to original sources

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↗

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↗

[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↗

[Principles of functional magnetic resonance tomography].

The basic principles of brain activation studies by MRI and functional spectroscopy are presented. The paper introduces the underlying mechanisms, followed by a discussion of the possibilities and limitations of current and new measuring techniques. Functional MRI has already proven to be a useful tool in neurocognitive research. Initial clinical applications have especially been demonstrated in neurosurgical operation planning.

Arousal↗

[Echo-planar imaging of the brain].

In this review, the clinical utility of echoplanar techniques in MRI of the brain is discussed. Comparison of high-resolution EPI with SE/turbo-SE shows high image quality of EPI in the supratentorial brain. In the infratentorial region, however, susceptibility artifacts limit image quality. For the assessment of neuronal brain activation utilizing the intrinsic contrast of blood (BOLD), EPI has definite advantages over other techniques of functional MRI. Due to its superior temporal resolution and multislice capabilities, EPI allows for analysis of complex neuronal activation patterns. Diffusion imaging benefits from the lack of bulk motion artifacts and serves primarily to detect early stroke. Three methods of perfusion imaging (rel. blood volume, rel. blood flow) are discussed: the susceptibility artifact method (T2*), the relaxitivity method (T1), and the signal-labelling technique (STAR). Perfusion imaging may have a clinical impact in the assessment of brain tumors and cerebral ischemia.

Artifacts↗

Detection of brain activation using oxygenation sensitive functional spectroscopy.

A nonwater-suppressed localized spectroscopy experiment using the PRESS-sequence has been used to study the signal changes of the water resonance during cortical activation. Significant effects with an effect-to-noise ratio up to 50:1 for a single shot experiment have been observed upon photic stimulation. The exceedingly high signal-to-noise ratio of the experiment was used to demonstrate signal changes as low as 0.1% after electrical stimulation of the median nerve.

Cerebral Cortex↗

Observation of a fast response in functional MR.

A spectroscopic MR technique was used to investigate the time course of the MR signal following a single visual stimulus. Gated experiments demonstrate there is an early response (500 ms after stimulus) leading to a reduction of the MR signal by -0.25% (P = 0.02), whereas a slower response (> 1500 ms after stimulus) results in a signal increase of +0.59% (P = 0.01). The fast negative response may be attributed to increased oxygen consumption, followed by a slower vascular response with overcompensation in blood oxygenation. This explanation would be in agreement with the blood oxygenation level dependent (BOLD) contrast mechanism considered the basis of functional MR. However, other physiological events might also be responsible for the signal drop observed.

Adult↗

Proton magnetic resonance spectroscopy studies on human brain myo-inositol in hypo-osmolarity and hepatic encephalopathy.

BACKGROUND/AIMS: Recent in vivo studies using proton magnetic resonance (1H-MR) spectroscopy showed low levels of myo-inositol in the brain in hepatic encephalopathy; the pathogenetic relevance of this observation is unclear. METHODS: Myo-inositol and glutamine levels in the brain were studied in vivo by 1H-MR spectroscopy in patients with hypo-osmolarity and hepatic encephalopathy. RESULTS: A patient with severe plasma hypo-osmolarity (222 mOsm/L) had almost undetectable signals for myo-inositol and glutamine/glutamate in the brain. Both signals reappeared after normalization of plasma osmolarity, suggesting that both myo-inositol and glutamine were released as organic osmolytes from the brain. A decreased cerebral myo-inositol signal is also found in low-grade hepatic encephalopathy but is accompanied by an increased glutamine signal. Cirrhotics without hepatic encephalopathy have near-normal inositol signals, and patients with acquired immunodeficiency syndrome encephalopathy have increased inositol signals. CONCLUSIONS: The 1H-MR spectroscopic myo-inositol signal in the human brain predominantly reflects an osmosensitive inositol pool. It is hypothesized that its depletion in latent hepatic encephalopathy points to a disturbance of cell volume homeostasis in the brain as an early pathogenetic event. This may partly be caused by a hyperammonemia-induced glutamine accumulation in the brain.

Acquired Immunodeficiency Syndrome↗

[Functional spectroscopy: the limits and potentials of a new method for the study of brain activation with MR tomography].

The possibility of examining brain activity by means of localised spectroscopy was studied in relation to its neurological basis. Measurements on 18 normals during optical stimulation showed an improvement in signal to noise ratio compared with functional imaging of almost one order of magnitude. Time dependent measurements during stimulation by a 500 ms light impulse showed definite delay of increased blood flow when compared with oxygen utilisation. The excellent signal to noise ratio and the inherent stability of the method permits reliable detection of weak effects such as are caused by finger tapping or electrical stimulation.

Artifacts↗

Organization and expression of the Escherichia coli K-12 dad operon encoding the smaller subunit of D-amino acid dehydrogenase and the catabolic alanine racemase.

A fragment of the Escherichia coli K-12 chromosome complementing the D-amino acid dehydrogenase and catabolic alanine racemase deficiency of a dad operon deletion mutant was cloned in a mini-Mu plasmid. The dadA and dadX genes were localized to a 3.5-kb part of the plasmid insert. The nucleotide sequence of this fragment revealed two open reading frames encoding 432- and 356-amino-acid-long proteins. We show here that they correspond to the dadA and dadX genes. The dadA gene can encode only the smaller of the two subunits of D-amino acid dehydrogenase. A computer search revealed the presence of a flavin adenine dinucleotide-binding motif in the N-terminal domain of the deduced DadA protein sequence. This is in agreement with biochemical data showing that the D-amino acid dehydrogenase contains flavin adenine dinucleotide in its active center. The predicted dadX gene product appeared to be 85% identical to a dadB-encoded catabolic alanine racemase of Salmonella typhimurium. The organization of the dadA and dadX genes confirmed our previous conclusion based on the genetic data (J. Wild, J. Hennig, M. Lobocka, W. Walczak, and T. Kłopotowski, Mol. Gen. Genet. 198:315-322, 1985) that these genes form an operon. The main transcription start points of the dad operon were determined by primer extension. They are preceded by a putative sigma 70 promoter sequence and two cyclic AMP-cyclic AMP receptor protein (cAMP-CRP) binding sites, one of higher and one of lower affinity to CRP. We propose that the high-affinity site, centered 59.5 bp upstream of the main transcription start point, plays a role in cAMP-CRP-mediated activation of dad operon expression in the absence of glucose.

Alanine Racemase↗

Biopsychological changes after bungee jumping: beta-endorphin immunoreactivity as a mediator of euphoria?

A study on 12 novice bungee jumpers was performed to investigate the influence of acute psychological stress on levels of cortisol in saliva, beta-endorphin immunoreactivity as well as the number of leukocytes in peripheral blood. In addition, heart rate and blood pressure as well as ratings on emotional states were recorded. Furthermore, correlations between ratings on mood and biochemical stress markers were computed. As expected, subjective ratings on anxiety were increased prior to the jump and were markedly reduced after the jump. Salivary cortisol was also increased after the jump and decreased to baseline within the next hour. In contrast, ratings on euphoria increased markedly after performing the jump and remained highly elevated for the next 30 min. An increase of more than 200% in beta-endorphin immunoreactivity after the jump was observed. In contrast to levels of cortisol, the concentration of beta-endorphin recorded immediately after the jump was significantly correlated with ratings on euphoria obtained at subsequent measurements indicating a relationship between beta-endorphins and euphoria. Additional increase of the number of blood leukocytes and of heart rate and blood pressure indicate that various systems of the organism are markedly affected by the exceptional eustress of bungee jumping.

Adult↗

Induction, modification, and perception of the salicylic acid signal in plant defence.

Endogenous salicylic acid (SA) levels increase and several families of pathogenesis-related genes (including PR-1 and PR-2) are induced during the resistance response of tobacco to tobacco mosaic virus (TMV) infection. We have found that at a temperature (32 degrees C) that prevents the induction of PR genes and resistance, the increases in SA levels were eliminated. However, when the resistance response was restored by shifting inoculated plants to lower temperatures, SA levels increased dramatically and preceded PR-1 gene expression and necrotic lesion formation associated with resistance. SA was also found in a conjugated form whose levels increased in parallel with the free SA levels. This SA beta-glucoside (SAG) was as active as SA in inducing PR-1 gene expression. PR-1 gene induction by SAG was preceded by a transient release of SA. The existence of a mechanism that releases SA from SAG suggests a possible role for SAG in the maintenance of systemic acquired resistance. Previously, we identified a soluble salicylic acid-binding protein (SABP) in tobacco whose properties suggest that it may play a role in transmitting the SA signal during plant defence responses. This SABP has been purified 250-fold by sequential chromatography on DEAE-Sephacel, Sephacryl S-300, Blue Dextran-Agarose and Superose 6. Several monoclonal antibodies (mAbs) raised against the highly purified SABP immunoprecipitated the SA-binding activity and a 280 kDa protein. This 280 kDa protein also co-purified with the SA-binding activity during the various chromatography steps, suggesting that it was responsible for binding SA. Immunoblot analysis with the SABP-specific mAbs also detected the 280 kDa protein in highly purified preparations of SABP. However, in crude homogenates these mAbs only recognized a 57 kDa protein. These and other results suggest that SABP is a multimeric complex which contains, at least, a 57 kDa protein and whose components are readily cross-linked during purification.

Carrier Proteins↗

In vivo proton spectroscopy of meningioma after preoperative embolization.

The time course of proton spectra of meningioma after embolization has been followed using a localized PRESS experiment with 135 ms of echo time. The most conspicuous findings were the observation of transient lactate signal within 24 h after blocking of the capillary bed. After that time large aliphatic signals from necrosis were observed, whereas other metabolite signals vanished. It was demonstrated, that tumor necrosis as shown by proton spectroscopy is complete within 4 days. This finding is significant for the timing of surgery, which can be performed after this period.

Adult↗

Magnetic resonance imaging in juvenile Canavan disease.

We present a 2-year-old boy and a 6-year-old girl with mild Canavan disease (CD). Aspartoacylase activity in skin fibroblasts was deficient. Magnetic resonance imaging (MRI) of the brain did not show the prominent leucodystrophy previously reported in CD, but there was a hyperintense signal from the lentiform nuclei and the heads of the caudate nuclei on the T2-weighted MR images. This suggests a specific vulnerability of the corpus striatum in these patients. In the older patient, the white matter became affected at the age of 6 years. Proton magnetic resonance spectroscopy (1H-MRS) of white matter revealed a normal concentration of N-acetyl-L-aspartate (NAA) and a markedly decreased concentration of choline containing compounds (Cho) in the boy but a normal ratio of NAA to Cho in the girl. We conclude that deficient NAA catabolism affects myelin metabolism. This may present as changes in the striatum and/or as a low concentration of Cho before leucodystrophy appears on MRI.

Amidohydrolases↗

Pathogen, salicylic acid and developmental dependent expression of a beta-1,3-glucanase/GUS gene fusion in transgenic tobacco plants.

The 5' flanking region of a gene encoding an acidic beta-1,3-glucanase from Nicotiana tabacum was isolated and characterized. A chimeric gene composed of 1759 bp of the promoter sequence from the PR-2 gene was fused to the beta-glucuronidase (GUS) coding region and used to transform tobacco. Transcriptional activation of the PR-2 promoter was investigated in response to inoculation with tobacco mosaic virus (TMV), after treatment of leaves with salicylic acid (SA), and in specific tissues during the normal development of healthy plants. In TMV-inoculated transgenic plants, GUS activity was induced locally around necrotic viral lesions and systemically in uninoculated leaves. GUS activity was also induced by treatment of leaves with SA. The chimeric gene was expressed in floral organs of healthy plants and in newly germinated seedlings. Analyses of a series of 5' deletions of the glucanase promoter indicated that the cis-acting elements necessary for induction by all these signals are localized in the region between -321 bp and -607 bp upstream of the transcription start site.

Amino Acid Sequence↗

Interconversion of the salicylic acid signal and its glucoside in tobacco.

Salicylic acid (SA) has been proposed to play a role in the induction of pathogenesis-related (PR) proteins and systemic acquired resistance (SAR) in tobacco. Since SA is rapidly converted to salicylic acid beta-glucoside (SAG) in tobacco, we have attempted to assess the role of SAG in pathogenesis by application of chemically synthesized SAG to tobacco leaves. SAG was as active as SA in induction of PR-1 gene expression. This induction was preceded by a transient release of SA, which occurred in the extracellular spaces. The existence of a mechanism that releases SA from SAG suggests a possible role for SAG in SAR.

Culture Techniques↗

Human brain tumors: assessment with in vivo proton MR spectroscopy.

To better understand variations in spectra of brain tumors, 122 in vivo proton spectra of brain tumors in 82 patients were analyzed. The changes in relative metabolite concentrations compared with those in normal spectra and the presence of any new metabolite were assessed. To evaluate the clinical usefulness of in vivo hydrogen-1 magnetic resonance (MR) spectroscopy in brain tumors, the authors looked for specific spectral changes on the basis of tumor grade. All tumor spectra showed differences from normal reference spectra. The differential diagnosis of the spectra was limited because intraindividual differences between spectra of one tumor at different locations were often larger than differences between spectra of tumors with different histologic characteristics. However, the variations in metabolite concentrations, and especially the presence or absence of aliphatic signals, were proved to be indicators of the histologic grade of tumor. The observed spectral patterns conformed to a four-compartment model, described herein, which is proposed to improve the interpretation of brain spectra.

Brain↗