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Query: UMLS:C0917798 (cerebral ischemia)
 17,036 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Image-guided localized proton magnetic resonance can now increasingly be used with clinical 1.5T MR systems. To fuel the discussion on whether spectroscopy will become a routine modality or whether it will remain a research tool, we report on our experience with a stimulated echo sequence in 60 patients harboring intracranial tumors and 79 patients suffering from various forms of cerebral ischemia. Spectroscopy was incorporated into a routine imaging protocol, and the parameters of TR = 1500 ms, TE = 270 ms were kept constant over a 3-year period. Relative changes in the metabolite concentrations were estimated from peak height and area calculations compared with the spectra of 66 normal volunteers. The spectra of the volunteers did not show significant interindividual variations, and there were no changes during photic stimulation in a subgroup of 6 volunteers. All tumor patients' spectra were significantly different from those of normal controls. Low grade gliomas showed decreased levels of N-acetyl-aspartate and some had elevated levels of lactate. Oligodendrogliomas had higher choline levels than astrocytomas. High grade gliomas had higher levels of lactate and lower N-acetyl-aspartate ratios. Meningiomas were characterized by absence of N-acetyl-aspartate, and some metastases showed a lipid signal at 1 ppm. Spectra of ischemic brain tissue were also abnormal, revealing lowered N-acetyl-aspartate and elevated lactate. The changes paralleled the severity of ischemia and pronounced abnormalities were associated with an inferior outcome. Further technical improvements, including absolute quantification of metabolite concentrations and smaller sensitive volumes, will allow direct monitoring of treatment.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:[1H magnetic resonance spectroscopy in intracranial tumors and cerebral ischemia]. 827 89

MR functional imaging, due to the improvement in ultra-speed imaging technology such as echo-planar imaging, has become a very powerful technique since the beginning of the nineties. This imaging technique is divided into diffusion imaging, perfusion imaging and cerebral activation. Diffusion imaging probes the mobility of water molecules characterized by a diffusion coefficient called the apparent diffusion coefficient (ADC) for biological tissues. Perfusion imaging gives hemodynamic information due to the regional cerebral blood volume by the use of contrast agents such as chelates of gadolinium carrying strong magnetic susceptibility. Both imaging techniques can provide information in a wide nosological range : cerebral ischemia, in the acute phase and in case of intracranial tumors, contributing to tumoral grading, localizing the site of biopsy, and assessing response to therapy (after radiotherapy for example). Nevertheless, a wide range of domains remains incompletely studied, for example cerebral white matter diseases and neurodegenerative diseases. For clinical applications, a precise knowledge of the potentials of both techniques and their limitations is needed. Limitations result from the large number of often patient-related parameters, imaging technique (perfusion) and data analysis. Powerful software has been developed in the workstation environment. Thus this imaging technique requires up-to-date equipment and close collaboration between clinical and research teams for optimal efficiency.
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PMID:[MR diffusion and perfusion imaging in clinical practice]. 1089 80