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Biomedical subjects

D Grucker

Publications and source records attributed to D Grucker.

At least 19 recordsLinked to original sources
PubMed2005

Functional integration in schizophrenia: too little or too much? Preliminary results on fMRI data.

The disconnectivity hypothesis proposes that schizophrenia results from poor or miswired anatomical connections. Theoretically, its functional counterpart should be disintegration. Integration is thought to allow segregated neurons to interact as a coherent whole, referred to as the "core", while the non-interacting part of the brain is referred to as the "rest". In this study, it is suggested that schizophrenia is the result of rest noise interfering with core activity. Two possible causes are assessed: (i) defective core integration, making the core more vulnerable to noise from the rest, or (ii) the rest being too highly integrated, meaning that it can interfere with the core. These hypotheses were tested using fMRI data acquired from 13 stabilized medicated schizophrenic subjects compared to 11 matched controls. Subjects were required to perform a series of lexical decision and retrieval tasks in separate sessions. The brain was divided into 90 components. Integration was defined as the amount of information shared between the components of a sub-system. An iterative aggregation procedure made it possible to identify a core on the basis of the functional clustering index, which assesses the integration of the core relative to its integration with the rest. Correlation of component-pairs within the core was also compared between the two groups. This procedure was repeated for each subject and for each task. Cores did not differ between the two groups, either in terms of integration or in terms of functional clustering index. However, the core was still highly integrated with the rest and the rest was overly integrated in schizophrenic subjects. Both anomalies were correlated with the negative symptoms. These findings were consistent regardless of the task considered. Furthermore, within the core, anterior-posterior correlations were lower in patients (between the frontal and the parietal and posterior cingulate cortices), whereas frontal left-right correlations were excessive. No significant correlation was found with the medication. Thus, it appears that schizophrenia entails a deleterious combination of too much "noisy" integration (from the rest) and too little "significant" integration (anterior-posterior functional connectivity).

Adult↗
PubMed2001

In vitro validation of MR measurements of arterial pulse-wave velocity in the presence of reflected waves.

A magnetic resonance imaging projective velocity encoding sequence was used to determine the pulse-wave velocity in an artery model. To this end, a well-defined flow phantom simulating flow propagation in large arteries was used. In order to validate the measurement method in the presence of large reflected waves, these were deliberately created in the phantom. The projective sequence was applied to two measurement sites and the wave velocity was determined from the spatial and temporal separations of the foot of the velocity waveform. A theoretical model describing reflection and attenuation phenomena was compared with experimental velocity waveforms. The model showed that reflections and attenuation can explain the important changes in velocity waveforms. The model also confirmed that in the presence of reflecting waves, the foot of the waveform can be used as a characteristic point for measurements through changes in the waveform.

Aorta↗
PubMed2001

7Li relaxation time measurements at very low magnetic field by 1H dynamic nuclear polarization.

Dynamic nuclear polarization (DNP) of water protons was used to measure the relaxation time of lithium at very low magnetic field as a demonstration of the use of DNP for nuclei less abundant than water protons. Lithium (Li+) was chosen because it is an efficient treatment for manic-depressive illness, with an unknown action mechanism. After having recalled the theoretical basis of a three-spin system comprising two nuclei-the water proton of the solvent, the dissolved Li+ ion and the free electron of a free radical-we have developed a transient solution in order to optimize potential biological applications of Li DNP. The three-spin model has allowed computation of all the parameters of the system-the longitudinal relaxation rate per unit of free radical concentration, the dipolar and scalar part of the coupling between the nuclei and the electron. and the maximum signal enhancement achievable for both proton and lithium spins. All these measurements have been obtained solely through the detection of the proton resonance.

Free Radicals↗
PubMed2000

Nuclear medicine image registration by spatially noncoherent interferometry.

UNLABELLED: This article introduces a technique for obtaining high-resolution body contour data in the same coordinate frame as that of a rotating gamma camera, using a miniature range finder, the conoscope, mounted on the camera gantry. One potential application of the technique is accurate coregistration in longitudinal brain SPECT studies, using the face of the patient (or "mask"), instead of SPECT slices, to coregister subsequent acquisitions involving the brain. METHODS: Conoscopic holography is an interferometry technique that relies on spatially incoherent light interference in birefringent crystals. In this study, the conoscope was used to measure the absolute distance (Z) between a light source reflected from the skin and its observation plane. This light was emitted by a 0.2-mW laser diode. A scanning system was used to image the face during SPECT acquisition. The system consisted of a motor-driven mirror (Y axis) and the gamma-camera gantry (1 profile was obtained for each rotation step, X axis). The system was calibrated to place the conoscopic measurements and SPECT slices in the same coordinate frame. RESULTS: Through a simple and robust calibration of the system, the SE for measurements performed on geometric shapes was less than 2 mm, i.e., less than the actual pixel size of the SPECT data. Biometric measurements of an anthropomorphic brain phantom were within 3%-5% of actual values. The mask data were used to register images of a brain phantom and of a volunteer's brain, respectively. The rigid transformation that allowed the merging of masks by visual inspection was applied to the 2 sets of SPECT slices to perform the fusion of the data. CONCLUSION: At the cost of an additional low-cost setup integrated into the gamma-camera gantry, real-time data about the surface of the head were obtained. As in all other surface-based techniques (as opposed to volume-based techniques), this method allows the match of data independently from the dataset of interest and facilitates further registration of data from any other source. The main advantage of this technique compared with other optically based methods is the robustness of the calibration procedure and the compactness of the sensor as a result of the colinearity of the projected beam and the reflected (diffused) beams of the conoscope. Taking into account the experimental nature of this preliminary work, significant improvements in the accuracy and speed of measurements (up to 1000 points/s) are expected.

Brain↗
PubMed1999

The pitfalls of planar three-phase bone scintigraphy in nontraumatic hip avascular osteonecrosis.

PURPOSE: This study documented the previously reported lower sensitivity of routine planar three-phase bone scintigraphy (BS) performed using a high-resolution parallel-hole collimator compared with MRI to diagnose nontraumatic avascular necrosis of the hip (AVN). METHODS: Six observers reviewed 143 bone scintigrams obtained in patients with nontraumatic hip pain (n = 120) or a control group (n = 23). All patients had a standard radiograph and MRI within 2 months of the BS. Of 280 hips, 148 (53%) were painful on the day of the examination. The osteonecrosis group (AVN) consisted of 93 instances of AVN in 58 patients. Although it departs from the clinical situation, this method evaluated the intrinsic performance of the imaging method. The data were analyzed using a receiver operating characteristic method. RESULTS: For the six observers, the A(z) values were 0.65, 0.67, 0.66, 0.67, 0.73, and 0.79, respectively, and 0.66, 0.71, 0.75, 0.81, 0.81, 0.82, and 0.84 after removing hip diseases other than AVN through data manipulation. Bone marrow edema, as seen on MRI, was the most frequently reported misleading sign in false-positive diagnoses, especially in the early or late phases of the disease. False-negative diagnoses misclassified the scans as "asymptomatic hips" in 28 of 30 cases. Twenty-two of 30 scans appeared normal, but these AVN lesions were small (<25%) and were discovered by chance on MRIs that displayed bilateral involvement associated with radiographic evidence (stage 0 or 1). Thirteen of 20 patients were followed for 3 or more years, and only one worsened. CONCLUSIONS: BS is not indicated to diagnose possible contralateral AVN if the hip is asymptomatic. This study emphasizes the results from the literature; if indicated, a radionuclide hip investigation requires the use of a pin-hole collimator, a SPECT study with scatter correction and iterative reconstruction algorithms, or both.

Adult↗
PubMed1998

Contribution of T2 relaxation time mapping in the evaluation of cryptogenic temporal lobe epilepsy.

In this study we compared the results of visual analysis of MR imaging with T2 relaxation time mapping of the mesial structures in a group of 97 patients with cryptogenic temporal lobe epilepsy. All patients underwent a clinical neurological examination, neuropsychological investigation, prolonged video-EEG monitoring, SPECT imaging, MR imaging, and T2 relaxation time mapping. T2 relaxation times were estimated with a Carr-Purcell-Meiboom-Gill pulse sequence with 48 echoes (15 to 720 ms). The mean T2 relaxation time value was 118.5 +/- 2 ms in the hippocampi and 120.3 +/- 1.9 ms in the amygdala of 21 healthy subjects used as controls. T2 relaxation mapping revealed mesial temporal sclerosis in 91.8% of the patients (often involving both the hippocampus and the amygdala) and evidenced bilateral involvement in 44.6% of the patients against 72.2 and 6.2%, respectively, for MR imaging. The ipsilateral and contralateral hippocampal T2 relaxation time values did significantly correlate with seizure frequency and the contralateral hippocampal T2 relaxation time value with the duration of epilepsy. In conclusion, this quantitative method is highly sensitive for the detection of mesial temporal sclerosis and permits a better evaluation of the apparently normal contralateral mesial structures.

Adolescent↗
PubMed1998

Registration of MR/MR and MR/SPECT brain images by fast stochastic optimization of robust voxel similarity measures.

This paper describes a robust, fully automated algorithm to register intrasubject 3D single and multimodal images of the human brain. The proposed technique accounts for the major limitations of the existing voxel similarity-based methods: sensitivity of the registration to local minima of the similarity function and inability to cope with gross dissimilarities in the two images to be registered. Local minima are avoided by the implementation of a stochastic iterative optimization technique (fast simulated annealing). In addition, robust estimation is applied to reject outliers in case the images show significant differences (due to lesion evolution, incomplete acquisition, non-Gaussian noise, etc.). In order to evaluate the performance of this technique, 2D and 3D MR and SPECT human brain images were artificially rotated, translated, and corrupted by noise. A test object was acquired under different angles and positions for evaluating the accuracy of the registration. The approach has also been validated on real multiple sclerosis MR images of the same patient taken at different times. Furthermore, robust MR/SPECT image registration has permitted the representation of functional features for patients with partially complex seizures. The fast simulated annealing algorithm combined with robust estimation yields registration errors that are less than 1 degree in rotation and less than 1 voxel in translation (image dimensions of 128(3)). It compares favorably with other standard voxel similarity-based approaches.

Algorithms↗
PubMed1998

Evaluation of Elecsys free triiodothyronine assay: relevance of age-related reference ranges.

OBJECTIVE: This study aimed at evaluating Elecsys free triiodothyronine (FT3) assay performed on an Elecsys 2010 system, while paying special attention to age relationship in euthyroid subjects. DESIGN AND METHODS: FT3 levels were measured in 149 euthyroid control subjects aged between 2 and 92 years old, 33 hyperthyroid and particular euthyroid patients: female in the last 3 months of pregnancy (n = 30), nonthyroidal ill hospitalized in medical (NTlm, n = 31), or intensive care units (NTlc, n = 31) and amiodarone-treated (n = 27). RESULTS: FT3 was inversely related to age in controls (r = -0.67). Three reference ranges were used: below 20 years 4.5-9.0 pmol/L, between 20 and 60 years 3.9-7.2, and over 60 years 2.4-6.5. Compared to age-matched controls, FT3 decreased in pregnancy, NTlm, NTlc, and amiodarone groups. Use of age-related reference ranges improved the specificity markedly in amiodarone patients and to a lesser extent in NTlm and TClc patients. CONCLUSIONS: The reliability of the Elecsys FT3 assay was found to be satisfactory for clinical use, when the age of patients was taken into account.

Adolescent↗
PubMed1998

Data-driven curvilinear reconstructions of 3D MR images: application to cryptogenic extratemporal epilepsy.

This paper presents a data-driven method for the reconstruction and visualisation of curvilinear slices from three-dimensional (3D) magnetic resonance (MR) scans of the head. Visualisation of curvilinear slices, rather than standard planar slices, produces symmetrical views of the cortex and allows small abnormalities to be detected by comparing the two hemispheres of the brain. In our method, the surface defined by the upper half of the brain is used as a reference shape for curvilinear reconstructions. The brain is first segmented from the 3D scan using a 3D region growing method associated to an unsupervised threshold selection technique. The upper half of the segmented brain is then extracted and fitted by a deformable surface model. This surface is finally interactively moved by the operator in the 3D scan, to visualise the desired curvilinear slice, which is projected on the screen as a two-dimensional image. We show an application of this visualisation technique to the localisation of cerebral epileptogenic lesions. The procedure has proven efficient and handy in clinical use.

Algorithms↗
PubMed1998

Dynamic nuclear polarization at very low magnetic fields.

The recent developments in dynamic nuclear polarization (DNP) at low magnetic fields are presented. The first part of the paper is dedicated to DNP theory for 14N nitroxide systems. It is shown that the lower the magnetic field, the higher the DNP factor. In the second part the material necessary to perform DNP in a low magnetic field is described. The third part is devoted to potential biological applications such as oximetry and free radical imaging.

Biophysical Phenomena↗
PubMed1998

Improved specificity of a new direct assay for urinary cortisol: application in corticoid treated patients.

Twenty four hours urinary free cortisol (UFC) excretion has been determined in 35 eucortisolic control patients, in seven of them before and after tetracosactide (Synacthen) stimulation and in 18 patients treated by anti-inflammatory steroids. Results of the new direct Immunotech RIA (DIm) were compared to those of the INCSTAR RIA kit with (ECA) or without methylene chloride extraction (DCA). In controls DIm UFC (106.2+/-45.8 nmol/24h) was significantly lower than DCA UFC (397+/-119 nmol/24h) and than ECA UFC (127+/-49 nmol/24h). After tetracosactide stimulation, median of DCA/DIm ratio decreased from 3.61 to 1.88 whereas ECA/DIm ratio did not change significantly (1.31 to 1.06). In treated patients most DCA and ECA results were over the upper limit of controls but only 5 DIm results were increased. DIm assay showed good specificity and practicability and may be used with benefit in the evaluation of the adrenal gland function.

Anti-Inflammatory Agents↗
PubMed1998

Video loop MRI of ocular motility: a new technique: turbo rare sequence at 2 T for the study of horizontal gaze.

PURPOSE: To improve existing MRI (Magnetic Resonance Imaging) methods of assessing ocular motility in horizontal gaze by using a multi-static fast imaging T2W MRI sequence, preventing patient head motion and convergence of the eyes during the study for the diagnosis and management of complex paralytic strabismus. SUBJECTS AND METHODS: A turbo-RARE image of the orbits was acquired in a set plane each time the patient fixed on a virtual image of one of 15 LEDs (Light Emitting Diodes). Positioning and securing the head was by a security cushion with an 8 degree tilt of the 25 cm quadrature head coil. After completion of the study (5 minutes) the MRI images were transferred to a work station and on to a magnetic-video tape to be replayed in cine mode on a PC using standard software. The qualitative analysis was completed by the study of quantitative parameters: visual axis, minor axis of the lens, the lines and angles of the horizontal rectus muscles with the optic nerve and the visual axis. We used digital image analysis to measure the cross-sectional areas of these muscles and also to determine muscle volumes. Twenty normal volunteers and 3 cases of oculomotor palsies were so studied. RESULTS: The experimental setup allowed us to obtain: 1) rapid (14 s) and high resolution images (256 x 196 x 3 mm); 2) which were free artifacts; 3) with no detectable eye convergence; 4) in which the lateral and medial rectus muscles and anatomical details of the orbit were clearly depicted; 5) from which additional functional information was obtained from the cine loop analysis; 6) wherein the visual axes did not converge during horizontal versions; 7) which permitted horizontal rectus muscle angles to be followed during contraction and relaxation; and 8) allowed the cross-sectional area of the four rectus muscles to be compared during contraction and relaxation (difference of 0.2 cm2). CONCLUSIONS: This method will provide useful functional quantitative information in the evaluation of ocular motility disorders. The procedure is readily clinically applicable

Convergence, Ocular↗
PubMed1996

New method for contrast manipulation in DNP-enhanced MRI.

The magnetization subtraction technique (MS), which is equivalent to the inversion recovery technique in strong magnetic fields, has been implemented in dynamic nuclear polarization-enhanced magnetic resonance imaging (DNPI). The general theoretical basis of the MS method, which can be applied to DNPI or to prepolarized MRI in weak magnetic fields (such as Earth's magnetic field), is introduced. Details are provided about the signal amplitude, dynamic range of the method, and conditions required to observe signal void in samples with specific T1 relaxation times. The experimental results obtained with MS DNPI are presented and discussed. In the experiments, electron spin resonance irradiation frequencies of 199 MHz and 16.2 MHz were employed. Also, T1 contrast manipulation in the polarizing and in the detection magnetic field is discussed and demonstrated for MS DNPI.

Image Enhancement↗
PubMed1995

Oximetry by dynamic nuclear polarization.

This study describes quantitatively the effect of O2 on the dynamic nuclear polarization (DNP) of water protons. It is shown theoretically how DNP enhancement is altered by the paramagnetism of O2. The nonlinear effect of oxygen on the enhancement factor has been approximated by a first order expression that provides accurate predictions of the experimental results obtained with phosphate-buffered solutions of 2,2,6,6 tetramethyl-4-oxo-piperidine-N-oxyl. The proton relaxation rates and DNP line width were measured for nitroxide concentrations ranging from 0.5 to 10 mM and for oxygen partial pressures ranging from 0 to 760 mmHg. A method is suggested for the calculation of the nitroxide and oxygen concentrations of a sample, based on two measurements, one with on-resonance EPR irradiation, the other with slightly off-resonance irradiation. Although the correlation between the values for the actual and calculated oxygen concentrations is good, the accuracy of the calculated oxygen concentration values remains poor, because of the large number of parameters involved in this calculation.

Algorithms↗