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Biomedical subjects

A Thron

Publications and source records attributed to A Thron.

At least 55 records · Page 3Linked to original sources
PubMed2001

Metabolic and electrophysiological validation of functional MRI.

OBJECTIVES: Although functional MRI is widely used for preoperative planning and intraoperative neuronavigation, its accuracy to depict the site of neuronal activity is not exactly known. Experience with methods that may validate fMRI data and the results obtained when coregistering fMRI with different preoperative and intraoperative mapping modalities including metabolically based (18)F-fluorodeoxyglucose PET, electrophysiologcally based transcranial magnetic stimulation (TMS), and direct electrical cortical stimulation (DECS) are described. METHODS: Fifty patients were included. PET was performed in 30, TMS in 10, and DECS in 41 patients. After coregistration using a frameless stereotactic system, results were grouped into overlapping (<1 cm distance), neighbouring (<2 cm), or contradictory (>2 cm). RESULTS: Comparing fMRI with PET, 18 overlapping, seven neighbouring, and one contradictory result were obtained. In four patients no comparison was possible (because of motion artefacts, low signal to noise ratio, and unusual high tumour metabolism in PET). The comparison of TMS and fMRI showed seven overlapping and three neighbouring results. In three patients no DECS results could be obtained. Of the remaining 38 patients, fMRI hand motor tasks were compared with DECS results of the upper limb muscles in 36 patients, and fMRI foot motor tasks were compared with DECS results of the lower limb on 13 occasions. Of those 49 studies, overlapping results were obtained in 31 patients, and neighbouring in 14. On four occasions fMRI did not show functional information (because of motion artefacts and low signal to noise). CONCLUSIONS: All validation techniques have intrinsic limitations that restrict their spatial resolution. However, of 50 investigated patients, there was only one in whom results contradictory to fMRI were obtained. Although it is not thought that fMRI can replace the intraoperatively updated functional information (DECS), it is concluded that fMRI is an important adjunct in the preoperative assessment of patients with tumours in the vicinity of the central region.

Adult↗
PubMed2001

Multimodality neuroimaging: research and clinical applications.

This manuscript reviews the current stance and the pertinent problems of transcranial magnetic stimulation (TMS) and functional magnetic resonance imaging (fMRI) as brain mapping methodologies. The missing structure-function relation limits the use of TMS, whereas the uncertainty about the functional significance of activated cortical regions might render interpretation of fMRI studies difficult. Advances in image processing, however, allowed for 3- dimensional real-time visual guidance of TMS and integration with fMRI data. We describe the method used to coregister TMS and fMRI and present examples where a multimodality neuroimaging approach might add to our understanding of normal and pathological brain function.

Brain Mapping↗
PubMed2001

Functional and diffusion-weighted magnetic resonance images of space-occupying lesions affecting the motor system: imaging the motor cortex and pyramidal tracts.

OBJECT: During neurosurgical interventions, preservation of subcortical axons is as important as preservation of cortical neurons. The goal of this study was to assess the combined use of functional (f) and diffusion-weighted (DW) magnetic resonance (MR) imaging to assist in the preservation of the structure and function of the motor system. METHODS: The authors evaluated the combination of fMR imaging and DW MR imaging to detect cortical motor areas with their corresponding pyramidal tracts in 12 healthy volunteers and in 10 consecutive patients with various space-occupying lesions affecting the central motor system. Activation within the primary motor cortex (M1) and white matter bundles originating from this cortical region was demonstrated in 21 of the 22 individuals examined. Additional activation was exhibited along the course of white matter tracts at the level of the pons and. in the contralateral hemisphere, in the M1. Fiber tract displacement was visualized in all patients in white matter that had appeared normal on routine T1- and T2-weighted MR images. CONCLUSIONS: The combination of DW MR and fMR imaging allows visualization of the origin, direction, and functionality of large white matter tracts. This will prove helpful for imaging structural connectivity within the brain during functional imaging. Moreover, local relationships of cerebral tumors that encroach upon M1 and subcortical fiber tracts can be defined. This promises to decrease patient morbidity and to broaden the clinical applications of functional imaging.

Adult↗
PubMed2000

Evidence of a smaller left hippocampus and left temporal horn in both patients with first episode schizophrenia and normal control subjects.

Findings from cerebral magnetic resonance imaging (MRI) studies in schizophrenia indicating temporal lobe involvement have been inconsistent and controversial. In a prospective study, we quantified the volumes of temporal lobe structures in 20 male patients with first episode schizophrenia (FES; mean+/-S.D.=27.4+/-4. 8 years) and 20 healthy age-matched male control subjects (27.7+/-3. 1 years). Measurements were performed on contiguous 2.2-mm coronal MRI slices, which included, as well as the temporal lobe, the amygdala, the hippocampal formation, and the temporal horn of the lateral ventricle. The definition of the borders of the structures relied on measurement guidelines derived from mutual comparisons of MRI and histological data. The definition of the hippocampus-amygdala interface was also validated in a correlated triplanar display. We did not detect any significant volume reductions of the measured structures in the FES group, as compared with healthy control subjects, on either side. Comparisons within groups, however, revealed that in both the patients and the healthy volunteers the hippocampal formations showed a significant right-sided bias (+9%, P=0.004, in the FES group; +12%, P=0.0003 in the control subjects). A significant volume difference in favor of the right hemisphere was also observed in the temporal horns of the lateral ventricles (+17%, P=0.02 in the patients with FES; +34%, P=0. 003, in the control group). There was only a nonsignificant trend for a larger temporal horn on the left side in patients with schizophrenia as compared with the control subjects. Our findings do not indicate a loss or reversal of the normal volume asymmetry pattern in the FES group.

Adult↗
PubMed2000

Hemodynamic changes in simple partial epilepsy: a functional MRI study.

We performed functional MRI (fMRI) on a patient with a mass lesion while she happened to experience a simple partial seizure. We used regional T2* signal changes to localize seizure-related hemodynamic changes. Seizure activity was associated with changes in MR signal in different regions that showed sequential activation and deactivation. Our study has shown that epileptic activity leads to changes in cerebral hemodynamics. In selected patients, therefore, it might be possible to use fMRI as a noninvasive tool to detect and investigate cortical patterns of activation associated with seizure activity.

Brain Neoplasms↗
PubMed2000

The representation of the plegic hand in the motor cortex: a combined fMRI and TMS study.

TMS mapping and fMRI were used to investigate changes in the motor cortex representation of the hand in a patient with complete loss of right hand function following traumatic avulsion of the cervical roots C7 and C8. Both TMS and fMRI demonstrated an expansion of the motor representation of the forearm into the hand area contralateral to the injured side. fMRI of the hand area, however, revealed that this area could still be activated when the patient was instructed to imagine finger tapping with his plegic hand. These results indicate that the plegic hand is still represented in the motor cortex, despite the fact that the same cortical area is also now active during movements involving forearm muscles.

Aged↗
PubMed2000

Cortical activation patterns during complex motor tasks in piano players and control subjects. A functional magnetic resonance imaging study.

We performed functional magnetic resonance imaging (MRI) in professional piano players and control subjects during an overtrained complex finger movement task using a blood oxygenation level dependent echo-planar gradient echo sequence. Activation clusters were seen in primary motor cortex, supplementary motor area, premotor cortex and superior parietal lobule. We found significant differences in the extent of cerebral activation between both groups with piano players having a smaller number of activated voxels. We conclude that, due to long-term motor practice a different cortical activation pattern can be visualized in piano players. For the same movements lesser neurons need to be recruited. The different volume of the activated ortical areas might therefore reflect the different effort necessary for motor performance in both groups.

Adult↗
PubMed2000

Presumed capillary telangiectasia of the pons: MRI and follow-up.

Capillary telangiectasia is a vascular abnormality primarily of the brainstem. The clinical relevance is unclear as is the association with clearly pathologic findings such as cavernous haemangioma. We report on four cases with capillary telangiectasia proven by follow-up and describe the imaging characteristics. T2 abnormality was only observed in half of the patients as was the presence of a discernable collecting vein. Whereas two cases were incidental findings in neurologically normal persons and one had symptoms clearly attributable to lacunar stroke, one patient may have had symptoms due to the vascular abnormality in the pons.

Adult↗
PubMed2000

Virtual pointer projection of the central sulcus to the outside of the skull using frameless neuronavigation -- accuracy and applications.

BACKGROUND: The purpose of this prospective study was to localize the central sulcus by frameless neuronavigation and to project this anatomical structure to the outside of the skull on the skin. This method was analyzed in respect to its practicability, accuracy, and potential applications. METHOD: In 27 patients investigated (28 unaffected hemispheres), the central sulcus was virtually projected to the outside of the skull using frameless neuronavigation and a virtual pointer elongation of 15 or 20 mm. The following parameters were measured on the scalp: 1. the distance between the bregma and the midline junction of the central sulcus, and 2. the angle between the central sulcus and the midline. These dada were compared with measurements based on the original axial MR images of these patients. Finally, a laboratory phantom study was designed in analogy to a patient's examination for estimation of the overall accuracy of the neuronavigation system in the experimental setup used in this study. FINDINGS: Virtual pointer projection of the central sulcus to the outside of the skull using frameless neuronavigation was found to be easily possible. The distance between the bregma and the midline junction of the central sulcus amounted to a mean of 55 mm on the left and 56 mm on the right. The angle between the central sulcus and the midline reached a mean of 63 degrees on the left and 60 degrees on the right. These data confirmed results of other studies with no frameless neuronavigation devices. The phantom study revealed a mean overall inaccuracy of 0.9 mm at a virtual pointer elongation of 15 mm. At a virtual pointer elongation of 20 mm, the mean overall inaccuracy of our study was 1.1 mm. These results correspond to the inaccuracy of frame based stereotaxy. INTERPRETATION: It is easily possible, valid, and reliable to virtually project the central sulcus to the outside of the skull with an acceptably low inaccuracy using frameless neuronavigation. This is important for research studies that correlate and integrate different functional imaging methods with the aid of frameless neuronavigation.

Adult↗
PubMed2000

Coil embolization of an incidental posterior cerebral artery aneurysm after initial OA-PCA bypass surgery.

Aneurysms of the posterior cerebral artery (PCA) are rare and imply a variety of treatment modalities. We present a case of an incidental, nonruptured posterior cerebral artery aneurysm, which was successfully occluded by coil embolization after a bypass between the occipital artery and the distal posterior cerebral artery was created. MR imaging in a neurologically normal 26-year-old man, performed in the course of a work-up for nonrelated symptoms, incidentally revealed a partially thrombosed and calcified aneurysm of the left posterior cerebral artery (P2 segment). This was confirmed by angiography. Due to aneurysm configuration and localization in the asymptomatic patient, primary clipping or endovascular occlusion was considered to be too hazardous. Four weeks after successful microvascular connection of the left occipital artery to the distal posterior cerebral artery, the PCA was occluded at the level of the aneurysm with a detachable coil. The patient remained asymptomatic, without visual field defects. The above presented combined microvascular (bypass) and endovascular (coil embolization) treatment with excellent result should be considered as alternative in patients with nonruptured, asymptomatic P2 aneurysms, which are high risk for primary clipping or endovascular occlusion.

Adult↗
PubMed2000

Experimental acute intracerebral hemorrhage. Value of MR sequences for a safe diagnosis at 1.5 and 0.5 T.

PURPOSE: To determine the detectability of intracerebral hematomas with MR imaging at 1.5 T and 0.5 T with fluid attenuated inversion recovery turbo spinecho (FLAIR) and gradient-echo sequences. MATERIAL AND METHODS: Twenty-seven intracerebral hematomas were created in 25 piglets by injection of venous blood into the brain through a burr hole. All were imaged with T2*-weighted gradient echo sequences (fast field echo, FFE), T2-weighted fluid attenuated inversion recovery turbo spin-echo sequences (FLAIR), T2-weighted turbo spin-echo (TSE) and T1-weighted spinecho sequences. Follow-up was performed on the 2nd, 4th and 10th postoperative days. Ten animals were additionally investigated with similar sequences at 0.5 T. Histologic correlation was obtained in all cases. RESULTS: T2* FFE sequences detected all acute intracerebral hematomas and demonstrated the size correctly at 1.5 T and 0.5 T. The conspicuity was better at 1.5 T. FLAIR sequences were unreliable in the hyperacute phase at 1.5 T: However. subarachnoid and intraventricular extension was best appreciated with FLAIR images. T2 TSE images were incapable of detecting paraventricular and subarachnoid hemorrhages, but clearly demonstrated intracerebral blood in other locations. TI-weighted images were insensitive to hemorrhage in the acute state but very useful in subacute and chronic hematomas. CONCLUSION: The safe and reliable diagnosis of intracerebral hemorrhage is probably possible with MR imaging at 1.5 T and 0.5 T even of hematomas less than 90 min old, but requires the application of at least FLAIR, T2* FFE and T1 sequences and is therefore time consuming.

Acute Disease↗
PubMed2000

The neural correlates of 'deaf-hearing' in man: conscious sensory awareness enabled by attentional modulation.

Attentional modulation of normal sensory processing has a two-fold impact on human brain activity: activation of a network of localized brain regions is associated with paying attention, and activation of specific sensory regions is enhanced relative to passive stimulation. The mechanisms underlying attentional modulation of perception in patients with lesions of sensory cortices are less well understood. Here we report a unique patient suffering from extensive bilateral destruction of the auditory cortices (including the primary auditory fields) who demonstrated conscious perception of the onset and offset of sounds only when selectively attending to the auditory modality. This is the first description of such an attentively modulated 'deaf-hearing' phenomenon and its neural correlates, using H(2)(15)O-PET. Increases in cerebral blood flow associated with conscious awareness of sound that was achieved by listening attentively (compared with identical auditory stimulation presented when the patient was inattentive) were found bilaterally in the lateral (pre)frontal cortices, the spared middle temporal cortices and the cerebellar hemispheres. We conclude that conscious awareness of sounds may be achieved in the absence of the primary auditory cortex, and that selective, 'top-down' attention, associated with prefrontal systems, exerts a crucial modulatory effect on auditory perception within the remaining auditory system.

Acoustic Stimulation↗
PubMed1999

[Value and safety of ambulatory electrophysiologic study].

One-hundred-thirty patients underwent 53 electrophysiological studies including programmed atrial and ventricular stimulation and 96 atrial overdrive stimulations on an outpatient basis. The indications for electrophysiological study were disabling palpitation, syncope, or presyncope, intracardiac conduction disturbance, and bradyarrhythmia. In one patient the efficacy of oral antiarrhythmic drug therapy was evaluated by repeat electrophysiological study. Atrial overdrive stimulation was performed in patients with atrial flutter or atrial tachycardia. On the basis of the result of electrophysiological testing, 25 patients were believed not to require any treatment, 16 patients received new drug therapy, 7 patients underwent catheter ablation in a second session, 2 patients had either a pacemaker or an ICD implanted, and 1 patient continued to receive the drug therapy that had been tested. Atrial overdrive stimulation resulted in a regular sinus rhythm in 66 patients (69%). Except for one patient in whom atrial flutter could not be terminated, atrial fibrillation was induced in the remaining 30 patients. After the procedure, patients were monitored for 30 min in case of overdrive stimulation, and for approximately 3 h after electrophysiological study or 6 h if additional coronary angiography had been performed. Severe complications were not observed. In 10 cases minor hematoma occurred at the puncture site without serious sequelae.--Outpatient electrophysiological study as well as atrial overdrive stimulation are feasible and safe in a selected group of patients.

Adult↗
PubMed1999

Long-term follow-up and outcome in patients treated for spinal dural arteriovenous fistula.

Clinical outcome was examined in 21 patients treated for spinal dural arteriovenous fistula after 5-50 months. We compared the neurological condition (motor function, pain, sensory disturbance, vegetative dysfunction) and Barthel index before and after fistula occlusion. Neurological impairment was assessed as improved, unchanged, or deteriorated. All patients initially showed paraparesis of varying degree, and a sensory loss with a defined level in 81% before treatment. The greatest postoperative change that we measured was in motor activity (67% improved), and the most important deterioration was in male potency (28% deteriorated). We observed unchanged or absent symptoms in pain in 71% of our patients. We were thus able not only to stop but even to reverse the progression of symptoms and the degree of disability. On average, neurological symptoms stabilized within 1 year. The results of this study confirm that spinal dural arteriovenous fistula should be treated as early as possible after diagnosis.

Adult↗
PubMed1999

Localization of the motor hand area using transcranial magnetic stimulation and functional magnetic resonance imaging.

OBJECTIVE: The anatomical location of the motor area of the hand may be revealed using functional magnetic resonance imaging (fMRI). The motor cortex representation of the intrinsic hand muscles consists of a knob-like structure. This is omega- or epsilon-shaped in the axial plane and hook-shaped in the sagittal plane. As this knob lies on the surface of the brain, it can be stimulated non-invasively by transcranial magnetic stimulation (TMS). It was the aim of our study to identify the hand knob using fMRI and to reveal if the anatomical hand knob corresponds to the hand area of the motor cortex, as identified by TMS, by means of a frameless MRI-based neuronavigation system. METHODS: Suprathreshold transcranial magnetic stimuli were applied over a grid on the left side of the scalp of 4 healthy volunteers. The motor evoked potentials (MEPs) were recorded from the contralateral small hand muscles, and the centers of gravity (CoG) of the MEPs were calculated. The exact anatomical localization of each point on the grid was determined using a frameless MRI-based neuronavigation system. In each subject, the hand area of the motor cortex was visualized using fMRI during sensorimotor activation achieved by clenching the right hand. RESULTS: In all 4 subjects, the activated precentral site in the fMRI and the CoG of the MEP of all investigated muscles lay within the predicted anatomical area, the so-called hand knob. This knob had the form of an omega in two subjects and an epsilon in the other two subjects. CONCLUSIONS: TMS is a reliable method for mapping the motor cortex. The CoG calculated from the motor output maps may be used as an accurate estimation of the location of the represented muscle in the motor cortex.

Adult↗
PubMed1999

Diagnostic accuracy of MRI compared to CCT in patients with brain metastases.

OBJECTIVES: In patients with extracranial neoplasms, the occurrence and number of brain metastases (BM) are critical for further diagnostic approaches and therapeutic strategies and the patient's prognosis. Although widely accepted, there is surprisingly little evidence in the literature that MRI is superior to CCT. Therefore, in patients with solitary BM according to diagnostic contrast-enhanced computed tomography (CCT), we investigated, what additional information could be gained by contrast-enhanced magnetic resonance imaging (MRI). METHODS/RESULTS: Among 55 patients with solitary BM according to CCT, 17 had multiple BM on MRI (31%) and 38 had solitary BM in both. Based on a presumed binomial distribution of our data, we calculated a rate of at least 19% of patients with solitary BM on CCT, in which MRI would show multiple lesions (p = 0.05). The two main characteristics for BM missed by CCT were the smaller diameter, which averages 2 cm less than in BM identified with both modalities, and a preferential frontotemporal location. CONCLUSION: MRI is indeed superior to CCT in the diagnosis of BM the essential reasons besides detection of smaller lesions being a better soft tissue contrast, significantly stronger enhancement with paramagnetic contrast agents, the lack of bone artifacts, fewer partial volume effects, and direct imaging in three different planes. Therefore, MRI is indispensable in the diagnostic workup of patients with BM for choosing the optimum therapeutic approach, especially with regard to the decision whether to operate or to primarily irradiate the patient's metastases.

Adolescent↗
PubMed1999

Clinical significance of intracranial developmental venous anomalies.

OBJECTIVES: Venous angiomas, or developmental venous anomalies (DVAs), represent the most often occurring cerebral vascular malformation. The clinical significance of a DVA is, however, at present unclear. METHODS: A retrospective analysis was carried out on two series of consecutive cranial MRIs performed between January 1990 and August 1996 in a university department of neuroradiology and in a large radiological private practice. The medical records of all patients in whom a DVA was diagnosed were screened to identify the specific complaint which necessitated the imaging procedure. RESULTS: A total of 67 patients with DVA could be identified. In 12 patients an associated cavernoma was found. The main reason for performing the MRI was the evaluation of seizures or of headaches. In all patients with DVA in whom an intracerebral haemorrhage was diagnosed an associated cavernoma was present at the site of the haemorrhage. None of the 67 patients showed an association between the complaints that led to the MRI and the location of the DVA. CONCLUSIONS: DVAs do not seem to be associated with a specific clinical presentation. In a significant percentage of cases, however, coexisting cavernomas are found which have a defined bleeding potential and should be treated independently of the DVA. This study supports the hypothesis that DVAs are a congenital abnormality of venous drainage without clinical significance.

Adult↗