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C M Segebarth

Publications and source records attributed to C M Segebarth.

8 recordsLinked to original sources
PubMed1999

fMRI assessment of hemispheric language dominance using a simple inner speech paradigm.

Hemispheric language dominance (HLD) has been determined by means of functional MRI (fMRI) using a simple, inner speech, word fluency paradigm. During the task periods, subjects perform mental imagery of visual scenes and generate silently the nouns of all objects visualized. During the control periods, subjects attend to the scanner noise. Activated areas have been identified by means of cross-correlation analysis. HLD indices have been determined by comparing the number of activated pixels detected in both hemispheres within predefined cortical areas (Brodmann areas 6, 9, 10, 39, 40 and 44-47). The paradigm has been assessed on 10 healthy, right-handed volunteers. A volume 35 mm thick, centered on the inferior frontal gyrus, was imaged. A conventional GRE MR sequence was used on a 1.5 T clinical MR scanner. HLD indices were compared with those determined for overt speech. Robust fMRI responses were obtained. HLD indices indicated left hemispheric language dominance for all subjects examined. They correlated well with those obtained for overt speech (R(2) = 0.93, regression coefficient = 0.998, with p < 10(-4)). Thus, an inner speech paradigm based on visual imagery is well adapted for assessment of HLD by means of fMRI.

Adult↗
PubMed1992

Excitation characteristics of adiabatic half-passage RF pulses used in surface coil MR spectroscopy. Application to 13C detection of glycogen in the rat liver.

Properties of sech/tanh and sin/cos half-passage RF pulses are discussed in view of their use in surface coil MR spectroscopy. We focus on the use of these pulses in a regime which is partially adiabatic, i.e. not strictly adiabatic off-resonance, while on-resonance the adiabaticity condition is fulfilled. It is shown that the frequencies of the singular points of the excitation profiles, as well as their number, depend on the B1 field. This leads to a signal intensity reduction from off-resonance spectral regions over much broader ranges than generally believed. We show in particular that with surface coil, sin/cos RF pulses may perform particularly well, providing optimal excitation on resonance and a desired attenuation over a broad spectral range off-resonance. This feature is applied for the in vivo detection of rat liver glycogen by means of 13C MR spectroscopy. Under suitable RF power conditions, a remarkable attenuation of the signals from the saturated carbons of the subcutaneous fat can be achieved.

Animals↗
PubMed1990

Detection of metabolic heterogeneity of human intracranial tumors in vivo by 1H NMR spectroscopic imaging.

Patients with intracranial tumors (gliomas) were examined by means of localized water-suppressed 1H NMR single volume spectroscopy and spectroscopic imaging. The 1H NMR spectra of the tumors exhibit signal intensities of the N-acetyl aspartate, choline compounds, and creatine plus phosphocreatine resonance lines that are different from the corresponding intensities observed on normal brain tissue. Also, for 6 out of the 10 patients examined so far, lactate resonance lines were detected in the tumor spectra. For one patient, abnormal 1H NMR spectra were obtained of a hemisphere which appeared normal with 1H NMR imaging. Metabolic heterogeneity of the tumorous regions could be demonstrated with 1H NMR spectroscopic imaging, using a spatial resolution in the order of 1 cm. These results suggest a spectrum of metabolic observations that may ultimately provide an important means for characterizing brain tumors.

Adult↗
PubMed1989

1H image-guided localized 31P MR spectroscopy of human brain: quantitative analysis of 31P MR spectra measured on volunteers and on intracranial tumor patients.

1H image-guided 31P MR spectra of normal human brain and of intracranial tumors have been analyzed quantitatively. Tumor types examined include prolactinoma, lymphoma, and various grade gliomas. The experimental signals were processed by means of a time-domain least-square fitting procedure, which yields the spectral parameters, as well as a prediction of the standard deviations. Significant spectral variations are observed within both populations of normal brain and of intracranial tumor 31P MR spectra. The metabolic ratios derived from the glioma 31P MR spectra and from corresponding uninfiltrated brain tissue do not differ significantly. Significant differences are, however, observed between the metabolic ratios of prolactinoma and uninfiltrated tissue 31P MR spectra. Alkaline pH values are found for the prolactinoma and the high-grade gliomas. Furthermore, spectral differences are observed between the patient's uninfiltrated tissue 31P MR spectra and those of an unmatched population of volunteers. This underscores the necessity for control measurements on the uninfiltrated tissue of the patient and for controls from a matched population of healthy individuals.

Adult↗
PubMed1987

MR image-guided P-31 MR spectroscopy in the evaluation of brain tumor treatment.

Magnetic resonance (MR) image-guided phosphorus-31 MR spectra have been obtained from in situ brain tumors. The volumes of interest used for spectroscopy were defined from hydrogen-1 MR images. Direct comparisons were possible between normal and abnormal tissue, since P-31 spectra from different parts of the brain could be measured in a single examination. P-31 MR spectra of the tumors often showed abnormally high concentrations of phosphomonoesters and low concentrations of phosphocreatines. The effects of pharmacotherapy and radiation therapy were studied in three patients; in each of these cases changes were observed in the P-31 spectra of the tumor. The correlation between MR imaging and P-31 MR spectroscopy was essential for the interpretations of these results.

Brain↗
PubMedDate not supplied

Quantitative 31P MRS of the normal adult human brain. Assessment of interindividual differences and ageing effects.

The characteristics of the 31P MR spectra from a large central volume in the brain of 47 healthy adults (aged 25-85 years) were assessed. Spectral parameters were estimated by means of a time-domain fitting technique. Statistical uncertainties of the estimates were determined by means of the Cramer-Rao theory and minimized by introducing a priori knowledge into the fitting procedure. Age-dependency of the spectral parameters was assessed by means of linear regression. Significant differences between individuals were established for some parameters. A significant age-dependency (p < or = 0.001) of ca 20% over the age range considered was found for the intensity of the phosphocreatine resonance line.

Adenosine Triphosphate↗
PubMedDate not supplied

Central processing of rectal pain: a functional MR imaging study.

BACKGROUND AND PURPOSE: Although the central processing of somatic pain has been dealt with in numerous brain imaging studies, the neural correlates of visceral pain have received much more limited attention. Our goal was to assess the feasibility of detecting brain activation patterns induced by rectal pain by means of functional MR imaging. We hypothesized that the cerebral processing of rectal pain would exhibit strong similarities with the central processing of somatic pain. METHODS: Functional MR imaging data were obtained from eight healthy subjects. A block paradigm was applied. Rectal pain was induced by inflating a latex balloon catheter that had been inserted into the rectum. Functional responses were established by means of cross-correlation analysis. RESULTS: Activation was detected within the anterior cingulate gyrus, the prefrontal cortex, the insular cortex, the sensory-motor cortex, the inferior parietal lobule, the posterior cingulate gyrus, and the visual cortex. CONCLUSION: Functional MR imaging of visceral pain is feasible in healthy subjects. The activation patterns observed in this study support the hypothesis that the cerebral processing of visceral pain involves multiple components, similar to the central processing of somatic pain. Our results constitute a first step toward the identification of possible aberrations in the activation patterns of patients suffering from visceral hypersensitivity.

Adult↗