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Biomedical subjects

U C Wieshmann

Publications and source records attributed to U C Wieshmann.

At least 19 recordsLinked to original sources
PubMed2003

Clinical application of neuroimaging in epilepsy.

OBJECTIVE: To evaluate the use of neuroimaging in clinical practice and to assess the prevalence of detected structural abnormalities in epilepsy patients in a clinical set up. METHODS: 919 outpatients were identified and the scan results reviewed. A total of 677 patients had chronic active epilepsy (88 had idiopathic generalised epilepsy (IGE), 588 had localisation related epilepsy, one had symptomatic generalised epilepsy), 57 had a single epileptic seizure, 46 were in remission, and 139 had non-epileptic attacks. RESULTS: 391 patients had no scan (53 patients in this group had IGE, 182 had localisation related epilepsy, one had generalised symptomatic epilepsy, 18 had single epileptic attacks, 21 were in remission, 116 had non-epileptic attacks). Altogether 528 patients had a scan, the results were not available in 33, 163 had x ray computed tomography (CT) only, 178 had standard magnetic resonance imaging (MRI) (slice thickness 5 mm), and 154 had high resolution MRI (including a T1 weighted sequence with 1.5 mm thick slices). Some 252 of 495 scans (51%) were abnormal. Abnormalities were hippocampal sclerosis (n=128), atrophy or non-specific white matter lesions (n=35), vascular abnormalities (n=27), tumours (n=25), brain damage (n=24), malformations of cortical development (n=13). Excluding atrophy and non-specific white matter lesions the prevalence of detected abnormalities was 54% in localisation related epilepsy, 18% in single seizure patients, 16% in epilepsy in remission, and 0% in IGE and non-epileptic attacks. CONCLUSIONS: Abnormalities were detected in more than half of all patients with localisation related epilepsy, and in about one in five patients with single seizures or epilepsy in remission. Many patients had no scan or only CT or standard MRI. The true prevalence of structural abnormalities may be have been higher. Scanning did not add any information in patients with IGE or non-epileptic attacks.

Adolescent↗
PubMed2003

Foramen ovale recordings: a presurgical investigation in epilepsy.

The aim of our study was to determine when foramen ovale recordings add useful information to scalp EEG recordings and magnetic resonance imaging (MRI) with hippocampal measurements. We evaluated the outcome of 79 patients with non-lesional partial epilepsy with presumed temporal seizure onset. Ictal foramen ovale recordings were performed in 16 patients with normal MRI ('MRI-negative group') and 41 patients with lateralizing MRI but non-lateralizing scalp EEG ('discordant group'). 22 patients with concordant MRI and scalp EEG were not investigated with foramen ovale recordings ('concordant group'). The seizure-free rate was higher in concordant than discordant patients despite additional investigation with foramen ovale electrodes (71 and 55% seizure free, respectively). No useful localizing information was added with foramen ovale recordings in MRI-negative patients.

Adult↗
PubMed2002

Voxel based morphometry of grey matter abnormalities in patients with medically intractable temporal lobe epilepsy: effects of side of seizure onset and epilepsy duration.

OBJECTIVES: To investigate the use of whole brain voxel based morphometry (VBM) and stereological analysis to study brain morphology in patients with medically intractable temporal lobe epilepsy; and to determine the relation between side, duration, and age of onset of temporal lobe epilepsy, history of childhood febrile convulsions, and grey matter structure. METHODS: Three dimensional magnetic resonance images were obtained from 58 patients with left sided seizure onset (LSSO) and 58 patients with right sided seizure onset (RSSO), defined using EEG and foramen ovale recordings in the course of presurgical evaluation for temporal lobectomy. Fifty eight normal controls formed a comparison group. VBM was used to characterise whole brain grey matter concentration, while the Cavalieri method of modern design stereology in conjunction with point counting was used to estimate hippocampal and amygdala volume. Age and sex were used as confounding covariates in analyses. RESULTS: LSSO and RSSO patients showed significant reductions in volume (using stereology) and grey matter concentration (using VBM) of the hippocampus, but not of the amygdala, in the presumed epileptogenic zone when compared with controls, but hippocampal (and amygdala) volume and grey matter concentration were not related to duration or age of onset of epilepsy. LSSO and RSSO patients with a history of childhood febrile convulsions had reduced hippocampal volumes in the presumed epileptogenic zone compared with patients without such a history. Left amygdala volume was also reduced in LSSO patients with a history of childhood convulsions. VBM results indicated bilateral thalamic, prefrontal, and cerebellar GMC reduction in patients, which correlated with duration and age of onset of epilepsy. CONCLUSIONS: Hippocampal sclerosis is not necessarily the consequence of recurrent temporal lobe seizures. A major cause of hippocampal sclerosis appears to be an early aberrant neurological insult, such as childhood febrile seizures. Secondary brain abnormalities exist in regions outside the presumed epileptogenic zone and may result from recurrent seizures.

Adolescent↗
PubMed2001

Combined functional magnetic resonance imaging and diffusion tensor imaging demonstrate widespread modified organisation in malformation of cortical development.

A patient with a mild left hemiparesis and a malformation of cortical development in the right hemisphere was investigated with fMRI (functional magnetic resonance imaging) and DTI (diffusion tensor imaging). The motor cortex was studied using a finger tapping fMRI experiment. The fibre orientation was studied by displaying the principal eigenvector of the diffusion tensor in the spatially normalised brain of the patient and of control subjects. In addition, the anisotropy (directionality) of water diffusion of the patient was statistically compared with control subjects. The malformation was located in the right central region in the expected position of the motor cortex. fMRI showed activation anterior and posterior to the malformation. DTI disclosed that fibres with rostrocaudal orientation, presumably representing the pyramidal tract, were deviating from their normal orientation and passing around the malformation. There were widespread regions of reduced anisotropy affecting both hemispheres. In conclusion, fMRI and DTI provided concordant information showing widespread modified functional and structural organisation including regions which appeared normal on standard imaging.

Adult↗
PubMed2000

Diffusion tensor imaging demonstrates deviation of fibres in normal appearing white matter adjacent to a brain tumour.

The objective was to study fibre orientation in the cerebral white matter of a patient with a brain tumour using diffusion tensor imaging (DTI). A patient with a mild left hemiparesis and a tumour in the right frontal lobe and 20 healthy volunteers were scanned with a DTI sequence. The scans were spatially normalised and the fibre orientation in the patient compared with the fibre orientation in normal controls. DTI disclosed a change of the orientation of fibres in the patient compared with normal controls. In the normal appearing white matter adjacent to the tumour fibres deviated from the normal superior inferior orientation in the corona radiata by about 30 degrees. This finding was consistent with a displacement by distant mass effect rather than a destruction of fibres, in agreement with the neurological examination. In conclusion, DTI demonstrated a deviation of fibres in normal appearing white matter adjacent to a tumour. The technique will improve understanding of the effects of structural abnormalities on fibres. This will assist the interpretation of clinical findings and functional imaging studies and guide neurosurgical interventions.

Brain↗
PubMed2000

Changes in cerebral hemodynamics during simple partial motor seizures.

Changes in cerebral perfusion were studied during nine short-lasting simple partial motor seizures (SPS) in an 11-year-old girl. Blood flow velocity changes in both middle cerebral arteries (MCAs) were assessed by transcranial Doppler sonography during simultaneous EEG monitoring. Within 7.4 +/- 1.4 s after electroencephalographic seizure onset, flow velocity in the MCA ipsilateral to the electrical discharges started to increase and then gradually rose up to 70% above baseline values. Spread of the epileptic activity to the other hemisphere in the late stage of seizure was associated with a slight increase in blood flow velocity (<30%) in the contralateral MCA. After the end of the seizure, flow velocities returned to baseline within 47 +/- 7 s. Our findings indicate that focal epileptic seizures evoke asymmetric perfusion increases which are closely related to the onset and cessation of the electroencephalographic seizure activity.

Blood Flow Velocity↗
PubMed1999

Anisotropy of water diffusion in corona radiata and cerebral peduncle in patients with hemiparesis.

Diffusion tensor imaging is a magnetic resonance method which provides quantitative measurements of the directionality (anisotropy) of diffusion. Anisotropy measurements can be used to obtain quantitative information about the microstructural integrity of white matter tracts. In intact tracts diffusion is restricted and directional because water molecules move predominantly longitudinally to tracts. The aim of this study was to measure the anisotropy of diffusion in patients with chronic hemiparesis. We measured in the corona radiata and the cerebral peduncle in 10 patients with a chronic hemiparesis and supratentorial lesions and 10 control subjects in regions of interest. In all patients anisotropy was reduced in the coronal radiata contralateral to the hemiparesis by more than 3 SD compared to control subjects. In three patients, each of which had a severe hemiparesis, anisotropy in the cerebral peduncle was reduced by more than 3 SD compared to normal control subjects. Our findings suggest that reduced anisotropy is associated with chronic hemiparesis.

Adult↗
PubMed1999

Water diffusion in the human hippocampus in epilepsy.

The hippocampus plays a central role in the generation and propagation of seizures in patients with complex partial seizures. Hippocampal sclerosis (HS) is a common structural abnormality in patients with refractory epilepsy. The aim of this study was to quantify diffusion in the hippocampus in patients with epilepsy to evaluate the diffusion changes associated with HS. We scanned 20 subjects (14 patients and 6 controls) with a 1.5T magnetic resonance (MR) system using a cardiac-gated, navigated spin-echo diffusion-weighted sequence. Hippocampal ADC measurements were performed on maps of the ADC measured in three orthogonal directions labeled x, y, and z. The mean ADC (ADCav) and an anisotropy index (AI) were calculated. Hippocampi which fulfilled the MR criteria for HS had a higher ADCav (p < 0.001) and a lower AI (p=0.04) than normal appearing hippocampi in patients and hippocampi in controls. These results imply a loss of structural organization in sclerotic hippocampi and an expansion of the extracellular space. Quantitative measurements of diffusion can be used as an independent parameter for the identification and characterization of abnormal hippocampi in epilepsy.

Adult↗
PubMed1999

Reduced anisotropy of water diffusion in structural cerebral abnormalities demonstrated with diffusion tensor imaging.

We used diffusion tensor imaging (DTI) to investigate the behavior of water diffusion in cerebral structural abnormalities. The fractional anisotropy, a measure of directionality of the molecular motion of water, and the mean diffusivity, a measure of the magnitude of the molecular motion of water, were measured in 18 patients with longstanding partial epilepsy and structural abnormalities on standard magnetic resonance imaging and the results compared with measurements in the white matter of 10 control subjects. Structural abnormalities were brain damage (postsurgical brain damage, nonspecific brain damage, perinatal brain damage, perinatal infarct, ischemic infarct, perinatal hypoxia, traumatic brain damage (n = 3), mitochondrial cytopathy and mesiotemporal sclerosis), dysgenesis (cortical dysplasia (n = 2) and heterotopia) and tumors (meningioma (n = 2), hypothalamic hamartoma and glioma). Anisotropy was reduced in all structural abnormalities. In the majority of abnormalities this was associated with an increased mean diffusivity; however, 30% of all structural abnormalities (some patients with brain damage and dysgenesis) had a normal mean diffusivity in combination with a reduced anisotropy. There was no correlation between fractional anisotropy and mean diffusivity measurements in structural abnormalities (r = -0.1). Our findings suggest that DTI is sensitive for the detection of a variety of structural abnormalities, that a reduced anisotropy is the common denominator in structural cerebral abnormalities of different etiologies and that mean diffusivity and fractional anisotropy may be, in part, independent. Combined measurements of mean diffusivity and fractional anisotropy are likely to increase the specificity of DTI.

Adolescent↗
PubMed1999

Hippocampal layers on high resolution magnetic resonance images: real or imaginary?

To evaluate whether the lines occasionally detected on clinical magnetic resonance (MR) images are genuine hippocampal layers, a formalin fixed hippocampal specimen was scanned using T2 weighted sequences at 7 Tesla (voxel dimensions 0.064 x 0.064 x 1 mm) and at 1.5 Tesla (voxel dimensions: 0.156 x 0.156 x 1 mm) and compared with the results of histological examination. In addition, a healthy volunteer was scanned with a T2 weighted sequence at 1.5 Tesla (voxel dimensions: 0.469 x 0.469 x 2 mm). On 7 Tesla images hippocampal layers and the granule cell layer of the dentate were visible. On 1.5 Tesla images of the specimen, the hippocampal layers were again identified, but the granule cell layer of the dentate was not detectable. On 1.5 Tesla images of the hippocampus in vivo, 3 layers could be distinguished in the hippocampus on some slices. These mainly represented the alveus, pyramidal cell layer and stratum radiatum. A dark line consisting of a few pixels possibly represented the dentate gyrus. Our results show that the lines occasionally detected on clinical MR images are likely to be real hippocampal layers. However, the resolution currently used in clinical imaging (typically 0.469 x 0.469 x 2 mm or lower) is not sufficient for the detection of all hippocampal layers. For the reliable detection of all hippocampal layers on MR images an increase by a factor of approximately 20 would be necessary.

Adult↗
PubMed1999

Wallerian degeneration in the optic radiation after temporal lobectomy demonstrated in vivo with diffusion tensor imaging.

PURPOSE: Diffusion tensor imaging allows the quantitative assessment of the microstructural organization of tracts in vivo (MR tractography). We used the new technique of MR tractography to demonstrate the effects of temporal lobectomy on the optic radiation. METHODS: Spatially normalised maps encoding magnitude of the bias (anisotropy) of diffusion of three patients with temporal lobe resections were compared with spatially normalised diffusion maps of 22 control subjects. All three patients were operated on for the treatment of medically intractable temporal lobe epilepsy and had a normal neurologic examination before surgery. One patient had an amygdalocorticectomy. Two patients had standard en bloc resections, one of whom developed a homonymous hemianopia after surgery. RESULTS: In the patient with hemianopia, a significant reduction of diffusion anisotropy (greater than mean+/-2 SD) consistent with wallerian degeneration was demonstrated in the optic radiation on the side of the temporal lobectomy, extending from the temporal to the occipital lobe. In the other patient with standard en bloc resection but clinically no hemianopia, the optic radiation was only marginally affected. In the third patient (amygdalocorticectomy), the diffusion anisotropy was within the normal range in the expected position of the optic radiation. CONCLUSIONS: Our findings show that MR tractography may be a useful tool to demonstrate wallerian degeneration in the optic radiation after temporal lobectomy in patients with hemianopia. This is the first time that this new method has been applied in postoperative imaging; it enables us to visualise the morphologic correlate of dysfunctional pathways after epilepsy surgery in vivo. The potential for using MR tractography to study other aspects of epilepsy is discussed.

Anisotropy↗
PubMed1999

Multimodal MR imaging: functional, diffusion tensor, and chemical shift imaging in a patient with localization-related epilepsy.

PURPOSE: To demonstrate the integration of complementary functional and structural data acquired with magnetic resonance imaging (MRI) in a patient with localization-related epilepsy. METHODS: We studied a patient with partial and secondarily generalized seizures and a hemiparesis due to a malformation of cortical development (MCD) in the right hemisphere by using EEG-triggered functional MRI (fMRI), diffusion tensor imaging (DTI), and chemical shift imaging (CSI). RESULTS: fMRI revealed significant changes in regional blood oxygenation associated with interictal epileptiform discharges within the MCD. DTI showed a heterogeneous microstructure of the MCD with reduced fractional anisotropy, a high mean diffusivity, and displacement of myelinated tracts. CSI demonstrated low N-acetyl aspartate (NAA) concentrations in parts of the MCD. CONCLUSIONS: The applied MR methods described functional, microstructural, and biochemical characteristics of the epileptogenic tissue that cannot be obtained with other noninvasive means and thus improve the understanding of the pathophysiology of epilepsy.

Adult↗
PubMed1998

Fast fluid-attenuated inversion-recovery imaging: first experience with a 3D version in epilepsy.

We developed a 3D version of fast fluid-attenuated inversion-recovery imaging (FLAIR) which provides images with a slice thickness of 1.5 mm. We present our initial experience with 3D fast FLAIR in patients with epilepsy. We compared 3D fast FLAIR (slice thickness 1.5 mm), 2D fast FLAIR (slice thickness 5 mm) and a 3D spoiled GRASS (IRSPGR) sequence (slice thickness 1.5 mm) in 10 patients with lesional epilepsy (head injury 1, hippocampal sclerosis 2, low-grade glioma 2, dysembryoplastic neuroepithelial tumour 2, polymicrogyria 1, perinatal infarct 1 and presumed thrombosed aneurysm 1). Both 2D and 3D fast FLAIR sequences yielded higher conspicuity for lesions than the T1-weighted IRSPGR sequence, except in the patient with polymicrogyria. The extent of the lesion, in particular that of low-grade tumours, was best assessed on 3D fast FLAIR images. 3D fast FLAIR may be a useful additional tool especially for imaging low-grade tumours.

Artifacts↗
PubMed1998

Image contrast and hippocampal volumetric measurements.

The objective was to assess the influence of image contrast on the repeatability of hippocampal measurements. We compared measurements on spoiled GRASS (SPGR) three-dimensional acquisition with measurements on inversion pulse prepared spoiled GRASS (IRSPGR) three-dimensional acquisition. IRSPGR images had a higher grey matter-white matter contrast than SPGR images. Repeated measurements of hippocampi of 13 subjects were performed on both SPGR and IRSPGR images and the standard deviation of the differences of repeated measurements calculated. SD was 239 mm3 for SPGR and 134 mm3 for IRSPGR. Our data suggest that higher image contrast improves the repeatability of hippocampal measurements.

Hippocampus↗
PubMed1998

The detection and significance of subtle changes in mixed-signal brain lesions by serial MRI scan matching and spatial normalization.

The purpose of this work is to detect and assess the significance of subtle signal changes in mixed-signal lesions based on serial MRI scan matching. Pairs of serially acquired T1-weighted volume MR images from 20 normal controls and seven patients with epilepsy were matched and difference images obtained. The precision and consistency of the registration were evaluated. The Gaussian noise level in the difference images was determined automatically. A structured difference filter was then used to segment structured (changed) voxels from the Gaussian noise. In the controls, the structured difference images were normalized into Talairach space, resulting in a structured noise map. The significance of changes in patients was assessed by spatial normalization and comparison with the structured noise map. The precision and consistency of the co-registration were < or = 0.06 mm with a registration success rate of 100%. The Gaussian noise level in the difference images was in the range 3.0-6.9. In the controls, an average of 1.6% of the brain voxels were classified as structured. Sine-based registration resulted in a reduction of < 1% in the amount of structure compared to linear interpolation. The structured noise map in controls showed high noise density in areas affected by image artefacts. We show examples of significant changes found in lesions which had been reported as unchanged on visual inspection. A novel quantitative approach has been presented for the detection and quantification of subtle signal changes in lesions. This method is of potential clinical value in the non-invasive characterization of signal change and biological behaviour of neoplastic lesions.

Adult↗