Multiple-quantum magic-angle spinning and double-rotation NMR techniques were applied in the high field of 17.6 T to the study of oxygen-17-enriched zeolites A and LSX with the ratio Si/Al = 1. A monotonic correlation between the isotropic value of the chemical shift and the Si-O-Al bond angle alpha (taken from X-ray data) could be found. Hydration of the zeolites causes a downfield 17O NMR chemical shift of about 8 ppm with respect to the dehydrated zeolites. Ion exchange of the hydrated zeolites generates stronger chemical shift effects. The increase of the basicity of the oxygen framework of the zeolite LSX is reflected by a downfield shift of approx. 10 ppm going from the lithium to the cesium form, and the substitution of sodium by thallium in the zeolite A causes a shift of 34 ppm for the O3 signal. 17O DOR NMR spectra are superior to 17O 3QMAS NMR spectra, featuring a resolution increase by a factor of 2 and are about equal with respect to the sensitivity. The residual linewidths of the signals in the 17O DOR and 17O 5QMAS NMR spectra can be explained by a distribution of the Si-O-Al angles in the zeolites.

Magnetic Resonance Spectroscopy↗

PubMedDate not supplied

[Is cerebral tomoscintigraphy with 99mTc-MIBI useful in the diagnosis of local recurrence in patients with malignant gliomas?].

PURPOSE: 99mTc-MIBI, an alternative radiopharmaceutical for myocardial perfusion study has been proposed for use as a tumor imaging agent, including breast cancer, lung cancer, lymphomas, melanomas, and brain tumors. After routine radiation therapy, deteriorating clinical status or treatment failure may be due to either radiation changes or recurrent tumor. CT and MRI offer imperfect discrimination of tumor viability and radionecrosis. MATERIALS AND METHODS: Thirty-five malignant glioma patients with clinical deterioration were studied retrospectively. Tomoscintigraphy was performed 15 minutes after intravenous injection of 1110 Mbq 99mTc-MIBI. The images were obtained from a dual headed gamma camera using fan beam collimator. Transverse, coronal and sagittal views were reconstructed. RESULTS: A dramatic MIBI uptake was found in 31 patients. This uptake was correlated to tumor recurrence proven by histological fragments and/or the rapid, fatal evolution of these patients. Death occurred after the brain SPECT had been performed for those cases showing MIBI uptake, an average 5.48 months later. No MIBI uptake was found for these four remaining patients: their evolution can be currently considered to be a disease-free time. CONCLUSIONS: According to our results, the sensibility and specificity of 99mTcMIBI brain SPECT seems to be high. Moreover, this investigation is more accurate for discriminating tumor recurrence from radionecrosis than a CT scan or MRI.

Adult↗

PubMedDate not supplied