PubMed Health⌕ Search

Biomedical subjects

F Lazeyras

Publications and source records attributed to F Lazeyras.

At least 19 recordsLinked to original sources
PubMed2006

Extent of preoperative abnormalities and focus lateralization predict postoperative normalization of contralateral 1H-magnetic resonance spectroscopy metabolite levels in patients with temporal lobe epilepsy.

BACKGROUND AND PURPOSE: Magnetic resonance (MR) spectroscopy can be used to determine the side of seizure onset in patients with temporal lobe epilepsy. Some patients with abnormal MR spectroscopy findings also have contralateral abnormalities, which in some cases have been reported to normalize after temporal lobe resection. With the aim of better understanding the mechanisms underlying abnormal MR spectroscopy findings, the current study was performed to define patient features that would predict this postoperative normalization. METHODS: Fifteen patients with temporal lobe epilepsy were subjected to preoperative and postoperative 1H-MR spectroscopy investigations, and the preoperative and postoperative metabolite levels in the contralateral hippocampus and contralateral lateral temporal lobe (CLTL) were determined. RESULTS: In the CLTL, postoperative normalization was more pronounced for patients showing extensive preoperative ipsilateral and contralateral abnormalities on MR spectroscopy. A second factor that influenced the degree to which the metabolite levels changed postoperatively was the focus lateralization. Surgery tended to have a more pronounced effect on the contralateral metabolite levels in patients with a right temporal focus, whereas in patients with left temporal foci, postoperative metabolite levels were virtually unchanged. In the contralateral hippocampal region, neither preoperative abnormalities nor focus side was related to postoperative normalization. CONCLUSIONS: We have thus identified 2 different factors (widespread preoperative MR spectroscopy abnormalities and right-sided focus) that predict postoperative normalization of contralateral MR spectroscopy abnormalities. We suggest that both factors indicate a more generalized epileptic disease (ie, that the patients in whom the MR spectroscopy abnormalities normalize are recovering from a more severe impairment).

Adult↗
PubMed2004

ADC mapping of the aging frontal lobes in mild cognitive impairment.

Normal aging, leukoaraiosis (LA) and vascular disease particularly involve the human frontal lobes. We decided to investigate a population of elderly patients referred for neuroimaging because of progressive minor cognitive deficits but no dementia. They underwent conventional Magnetic resonance imaging (MRI) using axial T1 and T2-weighted imaging as well as coronal FLAIR sequences in addition to the axial diffusion-weighted MRI. MRI allowed us to differentiate patients with leukoaraïosis (LA+) from those without it (LA-) and mapping of the apparent diffusion coefficient (ADC) to investigate local tissular water motion. We observed an increase in the ADC in all investigated patients with increasing age (r=0.326, p=0.002). This increase was observed in both patients groups (LA+ and LA-). In addition, the LA+ group had significant higher ADC values than the LA- group after controlling for age (p<0.0001).

Adult↗
PubMed2004

Diffusion-weighted MRI in cortical ischaemia.

We carried out MRI on 16 male and three female comatose patients, aged 2 days to 79 years, with suspected cortical ischaemia referred from our intensive care units. Using a head coil, and following standard imaging, including coronal fluid-attenuated inversion-recovery images, we performed diffusion-weighted imaging (DWI) using a whole-brain multislice single-shot echo-planar sequence with b 0 and 1000 s/mm2: 5-mm slices covering the whole brain, TR 7000 TE 106 ms, 128 x 128 pixels, field of view 250 mm, one excitation. Maps of apparent diffusion coefficients (ADC) were generated automatically. DWI showed cortical, basal ganglia and watershed-area high signal in all cases, associated with a decrease in ADC to 60- 80% of normal. DWI showed lesions not seen (40%) or underestimated (40%) on conventional T2-weighted imaging. Within 24 h of the onset of symptoms, DWI showed changes not readily detectable on T2-weighted images. The cortical high signal on DWI and the ADC changes, suggesting severe ischaemia rather than oedema, was found in areas known to be affected by cortical laminar necrosis. Extension to the brain stem and white matter was associated with a higher likelihood of death.

Adolescent↗
PubMed2004

Patients with extratemporal lobe epilepsy do not differ from healthy subjects with respect to subcortical volumes.

BACKGROUND: Evidence from previous volumetric magnetic resonance studies has revealed that patients with chronic temporal lobe epilepsy show atrophy of distinct subcortical nuclei, predominantly ipsilateral to the focus side. We were interested to find out if there is also selective subcortical atrophy in patients suffering from long standing extratemporal lobe epilepsy. METHODS: Thirty one patients in whom pre-surgical evaluation unambiguously localised an extratemporal focus were included in this study. Using high resolution magnetic resonance imaging, the volumes of the caudate nuclei, putamen, pallidum, and thalamus were measured bilaterally in both hemispheres and compared with measurements obtained in 15 healthy volunteers. RESULTS: No significant difference in volumes was found between the two subject groups, or in any subgroup of extratemporal lobe epilepsy patients, nor was there any relation to clinical variables such as age of onset, overall seizure frequency, or disease duration. However, patients who had no or only rare generalised tonic-clonic seizures seemed to differ from the other patients and controls in that they had smaller putamen volumes bilaterally (p<0.001). CONCLUSION: We concluded that extratemporal lobe epilepsy in general is not associated with diminished volumes in the studied subcortical structures, which contrasts with findings in temporal lobe epilepsy patients. Thus, both entities differ both cortically and subcortically. However, we found that small putamen volume was bilaterally associated with absent or rare generalised tonic-clonic seizures, implicating the putamen in the control of the most disabling seizure type, independent of the site of neocortical focus.

Adult↗
PubMed2003

Contralateral medial temporal lobe damage in right but not left temporal lobe epilepsy: a (1)H magnetic resonance spectroscopy study.

BACKGROUND: Proton magnetic resonance spectroscopy (MRS) of the hippocampus is useful in lateralising the epileptic focus in temporal lobe epilepsy for subsequent surgical resection. Previous studies have reported abnormal contralateral MRS values in up to 50% of the patients. OBJECTIVE: To identify the contributing factors to contralateral damage, as determined by MRS, and its extension in patients with temporal lobe epilepsy. METHODS: Single voxel MRS was carried out in the hippocampus and lateral temporal neocortex of both hemispheres in 13 patients with left temporal lobe epilepsy (LTLE) and 16 patients with right temporal lobe epilepsy (RTLE). All patients had mesial temporal lobe epilepsy with hippocampal sclerosis. Controls were 21 healthy volunteers of comparable age. RESULTS: Consistent with previous studies, the NAA/(Cho+Cr) ratio was abnormally low in the hippocampus ipsilateral to the focus (p < 0.0001), and there were lower values in both patient groups in the ipsilateral temporal neocortex (p < 0.0001). Patients with RTLE had left hippocampal MRS anomalies (p = 0.0018), whereas the right hippocampus seemed to be undamaged in LTLE patients. CONCLUSIONS: Unilateral mesial temporal lobe epilepsy is associated with widespread metabolic abnormalities which involve contralateral mesial and neocortical temporal lobe structures. These abnormalities appear to be more pronounced in patients with RTLE.

Adult↗
PubMed2001

Volumetric measurements of subcortical nuclei in patients with temporal lobe epilepsy.

OBJECTIVE: To determine the volumes of subcortical nuclei in patients with chronic epilepsy. BACKGROUND: Animal and human data suggest a crucial role for subcortical structures in the modulation of seizure activity, mostly as seizure-suppressing relays. Although cortical epileptogenic foci can vary in localization and extent, it nevertheless appears that these structures subsequently influence seizure propagation in a universal fashion. There is, however, little knowledge about the size of implicated subcortical structures in patients with epilepsy. METHOD: Using high-resolution MRI, the volumes of selected subcortical nuclei, such as the thalamus, caudate nucleus, putamen, and pallidum, were measured in both hemispheres of 27 patients with temporal lobe epilepsy. Fourteen healthy volunteers served as controls. Statistical analysis was done for both normalized volumes (by total brain volume) and unnormalized volumes. RESULTS: Overall, the patient group had smaller thalamic and striatal volumes in both hemispheres, mostly ipsilateral to the epileptic focus. No significant correlations were noted between volume measurements and age, age at onset, duration of epilepsy, or total seizure frequency, including frequency of generalized seizures. The putamen and thalamus seemed to be affected predominantly in patients with a history of febrile convulsions, whereas patients without febrile convulsions had smaller caudate nuclei bilaterally. CONCLUSIONS: Volumetric measurements of subcortical nuclei reveal atrophy of distinct subcortical nuclei in the patient group, predominantly ipsilateral to the focus. This finding probably reflects persistent abnormalities and not secondary change. In addition, the structural differences between patients with and patients without previous febrile convulsions suggest that these conditions may have different causes.

Adult↗
PubMed2001

Language representation in a patient with a dominant right hemisphere: fMRI evidence for an intrahemispheric reorganisation.

Studies have suggested that congenital left hemispheric (LH) frontal arteriovenous malformations (AVMs) are associated with an early transfer of language to right hemisphere (RH) frontal regions. The question remains whether such anatomofunctional reorganisation is due to RH compensatory abilities or to a general principle of lateral shift. In this study, we used fMRI language paradigms to investigate the case of a patient presenting aphasic symptoms following an haemorrhage due to a right frontal AVM. Prior to surgery, fMRI showed that language processing was confined to the RH, suggesting that language had not shifted during childhood from this congenitally dominant RH to the LH. After surgery, the patient presented severe aphasia that recovered to presurgical level within 70 days. At this time, fMRI showed that language tasks were still not associated with activations in the LH. These results suggest that the principles of early cerebral reorganisation after congenital lesions may differ in the RH and the LH. In addition, they support the idea that efficient restoration of language is achieved if a sufficiently large neuronal network is preserved around the lesion.

Adult↗
PubMed2001

FAST sequences optimization for contrast media pharmacokinetic quantification in tissue.

The purpose of this study was to investigate the influence of the fast gradient-recalled echo (GRE) sequence parameters on the contrast dynamic range and signal sensitivity, to optimize the magnetic resonance (MR) sequence for contrast media pharmacokinetic assessment. Effects of the fast low-angle shot (FLASH), Fast acquisition at steady rate (FAST), and radiofrequency-spoiled (RF)-FAST sequence parameters were studied in vitro. The FAST sequence had the highest sensitivity in low gadolinium (Gd) concentration. The FLASH and RF-FAST sequences had a larger contrast dynamic range, but the FLASH images contained side band artifacts. Increasing the flip angle to 90 degrees raised the sensitivity of the FAST sequence and the contrast dynamic range of the RF-FAST sequence. The shortest possible TE was optimal for both contrast dynamics and imaging time. TI had an influence on the sensitivity of the FAST sequence only for small acquisition matrices. This study indicates the optimal parameters for contrast dynamics (RF-FAST, 90 degrees flip angle, shortest possible TE) and sensitivity (FAST, 90 degrees flip angle, long TI(eff)).

Contrast Media↗
PubMed2001

Functional MRI with simultaneous EEG recording: feasibility and application to motor and visual activation.

The possibility of combining the high spatial resolution of functional magnetic resonance imaging (fMRI) with the high temporal resolution of electroencephalography (EEG) may provide a new tool in cognitive neurophysiology, as well as in clinical applications such as epilepsy. However, the simultaneous recording of EEG and fMRI raises important practical problems: 1) the patients' safety, in particular the risk of skin burns due to electrodes heating; 2) the impairment of the EEG recording by the static magnetic field, as well as by RF and magnetic field gradients used during MRI; and 3) the quality of MR images, which may be affected by the presence of conductors and electronic devices in the MRI bore. Here we present our experiences on 19 normal volunteers who underwent combined fMRI and 16-channel EEG examination. Consistent with previous reports, safety could be assured when performing EEG recordings during fMRI acquisition. Electrophysiological signals recorded with surface EEG were similar inside and outside the 1.5 T magnet. Furthermore, fMRI using motor or visual tasks revealed similar areas of activation when performed with and without 16-channel EEG recording. J. Magn. Reson. Imaging 2001;13:943-948.

Attention↗
PubMed2001

Dissociated active and passive tactile shape recognition: a case study of pure tactile apraxia.

Disorders of tactile object recognition (TOR) may result from primary motor or sensory deficits or higher cognitive impairment of tactile shape representations or semantic memory. Studies with healthy participants suggest the existence of exploratory motor procedures directly linked to the extraction of specific properties of objects. A pure deficit of these procedures without concomitant gnostic disorders has never been described in a brain-damaged patient. Here, we present a patient with a right hemispheric infarction who, in spite of intact sensorimotor functions, had impaired TOR with the left hand. Recognition of 2D shapes and objects was severely deficient under the condition of spontaneous exploration. Tactile exploration of shapes was disorganized and exploratory procedures, such as the contour-following strategy, which is necessary to identify the precise shape of an object, were severely disturbed. However, recognition of 2D shapes under manually or verbally guided exploration and the recognition of shapes traced on the skin were intact, indicating a dissociation in shape recognition between active and passive touch. Functional MRI during sensory stimulation of the left hand showed preserved activation of the spared primary sensory cortex in the right hemisphere. We interpret the deficit of our patient as a pure tactile apraxia without tactile agnosia, i.e. a specific inability to use tactile feedback to generate the exploratory procedures necessary for tactile shape recognition.

Adult↗
PubMed2001

Detection of experimental hepatic tumors using long circulating superparamagnetic particles.

RATIONALE AND OBJECTIVES: To evaluate the potential of an iron oxide-based MR contrast agent for the detection and delineation of experimental liver tumors during the early vascular phase of the compound. METHODS: Superparamagnetic blood pool agent (SBPA) was administered intravenously to rabbits bearing VX2 tumors. Images were acquired before the injection, immediately after, and 1 or 3 weeks later. The variations of signal intensity were measured in the tumors and in several tissues for various T1-weighted spin-echo, T2-weighted fast spin-echo, and T2-weighted gradient-recalled-echo sequences. RESULTS: Fourteen and 12 of the 16 tumors were detected immediately after SBPA injection using, respectively, the T2-weighted fast spin-echo and T2-weighted gradient-recalled-echo sequences. A significant decrease in signal intensity was observed in well-perfused organs, and blood signal was abolished even at the lowest injected dose and using a T1-weighted sequence. In the late phase, the loss in signal intensity of the liver was even more pronounced. CONCLUSION: The dominant T2 effect of SBPA induces an increase in the tumor-to-liver and tumor-to-blood contrast during the vascular phase, improving the detection of the tumors and allowing the distinction between small lesions and vessels through plane. This effect on the liver signal persists for several days because of the incorporation of SBPA in the reticuloendothelial system.

Animals↗
PubMed2001

EEG mapping and functional MRI in presurgical epilepsy evaluation.

The major goal of presurgical epilepsy evaluation is the correct and precise identification of the epileptic focus. Functional magnetic resonance imaging (fMRI) and EEG source analysis (EEG mapping) are two recent developments that are increasingly used in this particular clinical context. fMRI yields anatomically precise information but low temporal resolution, whereas the inverse situation is true for EEG mapping. Important complementary information is therefore obtained by integrating the results from each technique. Recent advances in these two fields are discussed, with particular reference to epileptic focus localization. Such a combined approach is shown to be a powerful tool, in particular in patients with non-lesional and/or extratemporal epilepsy still considered to be difficult surgical candidates.

Brain Mapping↗
PubMed2000

MRI, (1)H-MRS, and functional MRI during and after prolonged nonconvulsive seizure activity.

BACKGROUND: Various structural and functional changes, such as focal edema, blood flow, and metabolism, occur in the cerebral cortex after focal status epilepticus. These changes can be assessed noninvasively by means of MRI techniques, such as fluid-attenuated inversion recovery (FLAIR), EEG-triggered functional MRI (EEG-fMRI), and proton MR spectroscopy (MRS). METHODS: The authors report on a 40-year-old patient with nonlesional partial epilepsy in the left posterior quadrant in whom these MRI techniques were applied in an active seizure focus and repeated during a follow-up of 1 year. RESULTS: FLAIR imaging taken at the time of status epilepticus showed a signal hyperintensity in the occipital region. (1)H-MRS of this cortical region showed elevated lactate, decreased N:-acetylaspartate (NAA), and elevated choline (Cho). In the same region, EEG-fMRI revealed an area of signal enhancement. After seizure control, recovery of lactate and Cho was observed, whereas the NAA level remained reduced. The structural abnormality demonstrated on FLAIR disappeared within 3 months. CONCLUSIONS: Repetitive MRI with sensitive sequences during clinically critical periods may disclose the structural correlate in a previously nonlesional epilepsy case. Corresponding to the clinical evolution, reversible and irreversible focally abnormal metabolism can be determined with (1)H-MRS, reflecting both increased neuronal activity and neuronal damage.

Adult↗
PubMed2000

EEG-triggered functional MRI in patients with pharmacoresistant epilepsy.

Functional magnetic resonance imaging (fMRI) triggered by scalp electroencephalography (EEG) recordings has become a promising new tool for noninvasive epileptic focus localization. Studies to date have shown that it can be used safely and that highly localized information can be obtained. So far, no reports using comprehensive clinical information and/or long-term follow-up after epilepsy surgery in a larger patient group have been given that would allow a valuable judgment of the utility of this technique. Here, the results of 11 patients with EEG-triggered fMRI exams who also underwent presurgical evaluation of their epilepsy are given. In most patients we were able to record good quality EEG inside the magnet, allowing us to trigger fMRI acquisition by interictal discharges. The fMRI consisted of echoplanar multislice acquisition permitting a large anatomical coverage of the patient's brain. In 8 of the 11 patients the exam confirmed clinical diagnosis, either by the presence (n = 7) or absence (n = 1) of focal signal enhancement. In six patients, intracranial recordings were carried out, and in five of them, the epileptogenic zone as determined by fMRI was confirmed. Limitations were encountered a) when the focus was too close to air cavities; b) if an active epileptogenic focus was absent; and c) if only reduced cooperation with respect to body movements was provided by the patient. We conclude that EEG-triggered fMRI is a safe and powerful noninvasive tool that improves the diagnostic value of MRI by localizing the epileptic focus precisely.

Adolescent↗
PubMed2000

Absolute renal blood flow quantification by dynamic MRI and Gd-DTPA.

The aim of this study was to demonstrate the feasibility of the absolute renal blood flow quantification using MRI and injection of contrast media. Using a T1-weighted fast gradient sequence following an intravenous bolus injection of Gd-DTPA, dynamic images of the kidney were obtained in patients with well-functioning native kidneys (n = 7) or transplant (n = 9), with significant renal artery stenosis (n = 4) and with renal failure (n = 7). After signal intensity calibration, the absolute renal perfusion was equal to the wash-in slope of the renal transit curve divided by the contrast medium concentration at the peak of the bolus in the aorta. The cortical blood flow was 2.54+/-1.16 ml/min per gram in well-functioning kidneys decreasing to 1.09+/-0.75 ml/min per gram in case of renal artery stenosis (p = 0.04) and to 0.51+/-0.34 ml/min per gram in case of renal failure (P<0.001). These measurements were in agreement with previous results obtained by other methods. A standard MRI imaging sequence and a simple model can provide realistic quantitative data on renal perfusion. This work justifies further studies to compare this model with a gold standard for renal blood flow measurements.

Adult↗
PubMed2000

Magnetic resonance imaging and proton spectroscopic alterations correlate with parkinsonian signs in patients with cirrhosis.

BACKGROUND & AIMS: The relationship between abnormalities found by magnetic resonance imaging (MRI) and proton spectroscopy (MRS) and the clinical signs of hepatic encephalopathy is not well characterized. Motor disturbances have been described, suggesting that basal ganglia (BG) are altered. METHODS: We evaluated 19 unselected consecutive patients with biopsy-proven cirrhosis evaluated for liver transplantation for the presence of parkinsonian signs using the Unified Parkinson's Disease Rating Scale (UPDRS) and Purdue Pegboard test, and correlated these neurologic abnormalities with MRI and MRS studies. Brain MRI intensities were expressed as signal-to-noise ratios. MRS findings obtained from one voxel in the BG and one in the occipital white matter (WM) were expressed as metabolite ratios. Six healthy subjects had normal values. RESULTS: Compared with healthy subjects, patients with subclinical or grade 1 hepatic encephalopathy had hyperintensity in occipital WM and all BG tissues except thalamus and reduced Ino/Cr and Cho/Cr ratios in both voxels. In the BG, MRI intensity was correlated with the UPDRS (P < 0.05, r = 0.56). The Cho/Cr ratio also correlated with both UPDRS (P < 0.02, r = -0.59) and Pegboard scores (P < 0.02, r = 0.61). CONCLUSIONS: In cirrhosis, parkinsonian signs correlate with BG alterations detected by MRI and MRS.

Adult↗