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Biomedical subjects

C Kiefer

Publications and source records attributed to C Kiefer.

At least 19 recordsLinked to original sources
PubMed2003

Multiresolution fuzzy clustering of functional MRI data.

Recent developments in the analysis of functional MRI data reveal a shift from hypothesis-driven statistical tests to unsupervised strategies. One of the most promising approaches is the fuzzy clustering algorithm (FCA), whose potential to detect activation patterns has already been demonstrated. But the FCA suffers from three drawbacks: first the computational complexity, second the higher sensitivity to noise and third the dependence on the random initialization. With the multiresolution approach presented here, these weak points are significantly improved, as is demonstrated in our tests with simulated and real functional MRI data.

Algorithms↗
PubMed2003

Diffusion-weighted MRI in acute spinal cord ischaemia.

Acute spinal cord ischaemia is often undetectable with conventional MRI. Diffusion-weighted MRI (DWI) has been difficult to use in the spine because of susceptibility artefacts. We assessed the diagnostic value of echoplanar DWI for early confirmation of spinal cord ischaemia. We performed conventional MRI and DWI in two men and three women, aged 54-75 years with clinically suspected acute spinal cord ischaemia. Imaging was performed 9-46 h after the onset of symptoms, and 2-9 days later to assess the extent of ischaemic signal change. Spatial resolution of DWI within the spine using standard equipment was poor, but in all patients, early DWI revealed areas of high signal indicating decreased diffusion, confirmed by measurement of apparent diffusion coefficients. Follow-up MRI showed high signal on T2-weighted images and contrast enhancement at the expected levels. Neurological deficits corresponded with radiological findings in four patients: various syndromes, including isolated bilateral weakness or sensory change and combined deficits, were found. Echoplanar DWI may be helpful for confirmation of spinal cord ischaemia in the acute stage, but follow-up T2-weighted images have superior spatial resolution and correlation with clinical findings and lesion extent.

Acute Disease↗
PubMed2003

[Indications, effectiveness and tolerance of the rehabilitation techniques aimed at improving recovery of awareness following a traumatic brain injury].

OBJECTIVE: In the context of a consensus conference, this review aims at identifying through a comprehensive review and critical analysis of the literature the different rehabilitation programs used to promote the level of consciousness of brain injured patients. METHOD: By using the following data banks: Medline, Embase, Francis, Pascal, 97 articles published between 1980 and 2001 were found and 19 of them were finally selected. These 19 articles were synthesized through critical assessment charts. Six others articles, among those, expert opinion, literature reviews and consensus conferences were not assessed through critical assessment charts. RESULTS-DISCUSSION: Two non invasive interventions have been identified: these are sensory stimulation and sensory regulation. Neurostimulation, a surgical technique has not been discussed here. Most of the authors claim (16/19) for positive results. However, the major part of these studies contains serious methodological flaws which do not resist to critical analysis. CONCLUSION: Because of these methodological flaws and despite the good results claimed by the authors, there is up to date no evidence that clearly demonstrate the effectiveness of sensory stimulation or sensory regulation programs. Further clinical research in this area is necessary.

Awareness↗
PubMed2003

[Clinical evaluation of spasticity].

Spasticity is one component of the upper motor neurone syndrome. Unlike motor deficit and co-contraction, spasticity is responsive to treatment. Thus it receives more attention than the other features of the upper motor neuron syndrome. In order to treat correctly the patients, we need to know expectations of the patient and family. Detailed clinical evaluation including functional analysis is necessary to determine whether the objectives are reasonable. This evaluation is not always very easy because of complex clinical features. Simply aiming to reduce spasticity is not a final treatment goal. There must be a purpose behind it. It is actually very difficult to evaluate functional effect of spasticity treatments. Few studies show a real functional improvement. Yet patients are satisfied with the results and the goals are often achieved. One explanation is that functional scales usually used do not fit to the spasticity problem.

Humans↗
PubMed2003

[Surgical treatment of orthopedic deformities due to spasticity in the lower limb].

Orthopedic deformities in the lower limb concern all joints (hip, knee, ankle, foot) with a wide range of clinical forms. Spasticity, contracture, stiffness, laxity, neurological deficit are assessed to establish the surgical procedure. Surgical techniques are adapted to the goals that are detailed with the patient and his family: standing, transferring, walking, hygiene, devices (shoes, orthosis, canes, wheelchair). Surgical procedures can associate: lengthening of contractured muscles (tenotomy with or without sutures, fractional lengthening at the musculo-tendinous junction or desinsertion), strengthening of antagonists (passive or active tendon transfer) and correction of joint deformity (arthrolysis, arthrodesis, arthroplasty). In adults, the most common deformities are the equinus or equinovarus foot, toe curling, hip adductum, knee flessum. Talus or knee recurvatum are less frequently observed. The association of various deformities raises questions concerning the hierarchy of surgical procedure, from an anatomical point of view (do we start with proximal or distal joint first?) as from chronological concerns (shall we do one or more procedures?). Pluridisciplinary assessment using neurological anesthetic blocs and dynamic EMG or gait analysis is necessary to detail the aims of surgery and choose the surgical procedures.

Foot Deformities, Congenital↗
PubMed2002

Apparent diffusion coefficient mapping of infarcted tissue and the ischaemic penumbra in acute stroke.

MRI assessment of diffusion changes in acute cerebral ischaemia necessitates analysis of the apparent diffusion coefficient (ADC). We used the concept of relative weighted mean ADC (rwmADC) to obtain an accurate estimate of the extent of infarcted tissue. We studied ten patient with of acute ischaemic stroke, using diffusion- and perfusion- weighted MRI. The rwmADC was used to calculate a corrected ADC-lesion volume (DLVR), which was compared with the diffusion-lesion volume (DLV), initial perfusion lesion volumes and the follow-up infarct volume on T2-weighted images. We looked at correlations between the MRI and clinical findings. DLVR was closest to the final infarct size and had the best clinicoradiological correlation (r=0.77). Weighting the mean ADC within the ischaemic and normal parenchyma can give a more correct estimate of the volume of infarcted brain parenchyma, thus improving the definition of the penumbra.

Brain↗
PubMed2002

Diffusion and perfusion MRI for the localisation of epileptogenic foci in drug-resistant epilepsy.

Drug-resistant epilepsy is an important clinical challenge, both diagnostically and therapeutically. More and more surgical options are being considered, but precise presurgical assessment is necessary. We prospectively studied eight patients with drug-resistant epilepsy, who underwent clinical examination, single photon emission computed tomography (SPECT) and interictal MRI, including diffusion- and perfusion-weighted echoplanar sequences. Lesions suspected on SPECT of being epileptogenic showed mild hypoperfusion, while the diffusion-weighted MRI (DWI) revealed increased apparent diffusion coefficients relative to the other side. However, these abnormalities were not visible on the corresponding maps. We showed that DWI and perfusion-weighted MRI could be used confirm the characteristics and site of an epileptogenic area in patients with drug-resistant epilepsy.

Adolescent↗
PubMed2002

Slow rhythmic oscillations in intracranial CSF and blood flow: registered by MRI.

Since Lundberg first described slow oscillations as so called B-waves during ICP-monitoring, similar oscillations have been found in various physiological systems. Thus, the detection of slow waves in intracranial CSF- and blood-flow with MR-techniques seemed very likely. We examined the interventricular CSF-flow and cerebral blood flow of 11 healthy volunteers with dynamic echo-planar imaging by simultaneous registration of respiration and peripheral pulse. The spectral analysis was restricted to slow waves, which were divided into B-waves (0.008-0.05 Hz), Mayer- or C-waves (0.05-0.15 Hz) and respiration-related waves (0.15-0.6 Hz). In the CSF, the integrated amplitude of B-waves accounted for 18.2%, Mayer- or C-waves for 26.9% and respiration-related waves for 55.0%. Proportional values were recorded in the artery and peripheral pulse. In the venous sinus, a higher percentage of B- and Mayer-/C-waves and a lower percentage of respiration related waves were found. In conclusion, with MR-EPI technique, slow rhythmic oscillations in the cerebral blood- and CSF-flow can be analysed non-invasively and independently from the cardiac cycle. The comparable distribution of slow waves in the pulse, arteries and CSF may reflect an origin in autoregulation, whereas divergent patterns like in the incompressible venous sinus may be of a passive origin.

Adolescent↗
PubMed2001

Focal status epilepticus: follow-up by perfusion- and diffusion MRI.

Diffusion-weighted MRI demonstrated bright right temporoparietal cortex, right hippocampus, and left cerebellum in a 63-year-old female suffering a focal convulsive status epilepticus. Hyperperfusion was noted in the right temporoparietal region. Two days later, a tendency to normalization of most of the diffusion and perfusion changes was noted, apart from the right hippocampus which became brighter on diffusion- and T2-weighted images. On the tenth day the apparent diffusion coefficient was slightly elevated, getting brighter on T2-weighted images with suspected mild post-contrast enhancement. We postulate that the discharging right hippocampus suffered cytotoxic edema, which later progressed to cell damage.

Brain↗
PubMed2001

Identification and characterization of a mammalian enzyme catalyzing the asymmetric oxidative cleavage of provitamin A.

In vertebrates, symmetric versus asymmetric cleavage of beta-carotene in the biosynthesis of vitamin A and its derivatives has been controversially discussed. Recently we have been able to identify a cDNA encoding a metazoan beta,beta-carotene-15,15'-dioxygenase from the fruit fly Drosophila melanogaster. This enzyme catalyzes the key step in vitamin A biosynthesis, symmetrically cleaving beta-carotene to give two molecules of retinal. Mutations in the corresponding gene are known to lead to a blind, vitamin A-deficient phenotype. Orthologs of this enzyme have very recently been found also in vertebrates and molecularly characterized. Here we report the identification of a cDNA from mouse encoding a second type of carotene dioxygenase catalyzing exclusively the asymmetric oxidative cleavage of beta-carotene at the 9',10' double bond of beta-carotene and resulting in the formation of beta-apo-10'-carotenal and beta-ionone, a substance known as a floral scent from roses, for example. Besides beta-carotene, lycopene is also oxidatively cleaved by the enzyme. The deduced amino acid sequence shares significant sequence identity with the beta,beta-carotene-15,15'-dioxygenases, and the two enzyme types have several conserved motifs. To establish its occurrence in different vertebrates, we then attempted and succeeded in cloning cDNAs encoding this new type of carotene dioxygenase from human and zebrafish as well. As regards their possible role, the apocarotenals formed by this enzyme may be the precursors for the biosynthesis of retinoic acid or exert unknown physiological effects. Thus, in contrast to Drosophila, in vertebrates both symmetric and asymmetric cleavage pathways exist for carotenes, revealing a greater complexity of carotene metabolism.

Amino Acid Sequence↗
PubMed2001

Analysis of the blind Drosophila mutant ninaB identifies the gene encoding the key enzyme for vitamin A formation invivo.

Visual pigments (rhodopsins) are composed of a chromophore (vitamin A derivative) bound to a protein moiety embedded in the retinal membranes. Animals cannot synthesize the visual chromophore de novo but rely on the uptake of carotenoids, from which vitamin A is formed enzymatically by oxidative cleavage. Despite its importance, the enzyme catalyzing the key step in vitamin A formation resisted molecular analyses until recently, when the successful cloning of a cDNA encoding an enzyme with beta,beta-carotene-15,15'-dioxygenase activity from Drosophila was reported. To prove its identity with the key enzyme for vitamin A formation in vivo, we analyzed the blind Drosophila mutant ninaB. In two independent ninaB alleles, we found mutations in the gene encoding the beta,beta-carotene-15,15'-dioxygenase. These mutations lead to a defect in vitamin A formation and are responsible for blindness of these flies.

Amino Acid Sequence↗
PubMed2000

Robustness and diffusion of pointer states

Classical properties of an open quantum system emerge through its interaction with other degrees of freedom (decoherence). We treat the case where this interaction produces a Markovian master equation for the system. We derive the corresponding distinguished local basis (pointer basis) by three methods. The first demands that the pointer states mimic as closely as possible the local nonunitary evolution. The second demands that the local entropy production be minimal. The third imposes robustness on the inherent quantum and emerging classical uncertainties. All three methods lead to localized Gaussian pointer states, their formation and diffusion being governed by well-defined quantum Langevin equations.

Journal Article↗
PubMed2000

Detection of a relation between respiration and CSF pulsation with an echoplanar technique.

The flow of cerebrospinal fluid (CSF) through the aqueduct was studied with an echoplanar imaging technique. Images (1024) of a slice perpendicular to the aqueduct were acquired with a repetition time of 107 msec and a flip angle of 90 degrees. This imaging technique is very sensitive for flow into the selected slice, although a quantitative assessment of flow velocities is not possible. Simultaneously with the image data acquisition, data from a pulse oximeter and a respiration belt were recorded. For each data point, a delay time to the preceding cardiac pulse was determined from the recorded pulse wave. The signal intensities could then be assigned to the cardiac cycle. Each cardiac interval was assigned to one of eight respiratory phases, and an average signal curve during the cardiac interval was calculated for each respiration phase. The evaluation showed to signal maxima within the cardiac interval, which could be identified as a downward flow at 10% and an upward flow at 80% of the cardiac pulse interval by measurements with additional saturation pulses. In examinations of 22 healthy volunteers, an influence of respiration on the flow through the aqueduct was found. In spite of interindividual variability, comparable effects could be observed in all volunteers. In the late expiration phase the caudally directed flow was at its maximum, whereas the cranially directed flow was maximal in the post-inspiration phase.

Adult↗
PubMed1996

Increased sensitivity of the inositol-phospholipid system in neutrophils from patients with acute major depressive episodes.

Evidence from in vitro and in vivo studies suggests that the therapeutic and prophylactic effects of lithium in recurrent affective disorders are due to an attenuation of the inositol-phospholipid (IPL) second messenger system. An increased sensitivity of this signal transduction system might therefore constitute a risk factor for affective illness. The extent of the agonist-induced release of intracellular Ca2+ (Ca2+ response) can be used as an indicator of the sensitivity of the IPL system. Using this paradigm, we have measured the agonist-induced Ca2+ response in neutrophils of 17 unmedicated patients who were experiencing an acute major depressive episode. The neutrophils were stimulated by the chemotactic peptide formylmethionylleucylphenylalanine, which activates the IPL system in the cells. The sensitivity of the IPL system in these patients was significantly greater (dose-response curve shifted to the left) compared with its sensitivity in healthy age- and sex-matched control subjects. The results indicate that acute episodes of major depression are associated with an increased sensitivity of the IPL system.

Adult↗