In vitro evaluation of platinum Guglielmi detachable coils at 3 T with a porcine model: safety issues and artifacts.

PURPOSE: To evaluate safety-related issues and imaging artifacts of Guglielmi detachable coils in vitro with 3-T magnetic resonance (MR) imaging. MATERIALS AND METHODS: Two aneurysm models were constructed: one from porcine carotid artery and the other from a pharmaceutical capsule. Both were filled with Guglielmi detachable coils. The models were tested with a 3-T MR imager for heating, deflection, and imaging artifact. Testing for heating and deflection was performed (a) at static points both inside and outside the bore, (b) during movement into the imager, and (c) during clinical imaging sequences. RESULTS: No change in temperature was measured during movement into the imager bore or at different points within the bore. No differences in heating from radio-frequency energy were found between aneurysm models and controls. Similarly, no evidence of deflection of the coil mass (capsule model) was found. Minor susceptibility artifacts were found in the readout direction during gradient-echo sequences. Magnetic field mapping showed no induced field inhomogeneity. CONCLUSION: MR imaging at field strengths of 3 T in patients with aneurysms treated with Guglielmi detachable coils is safe. Imaging artifacts are likely to be minimal.

Understanding the discrepancies between 31P MR spectroscopy assessed liver metabolite concentrations from different institutions.

The high divergence between the liver metabolite concentrations and pH values reported in previous quantitative 31P magnetic resonance studies, for instance phosphomonoester (0.7-3.8 mM) and phosphodiester (3.5-9.7 mM), has not been addressed in the literature. To assess what level of discrepancy can be caused by processing and metabolite integration, in this study chemical shift imaging localized 31P magnetic resonance spectra of human liver were quantitated by three methods currently applied in clinical practice: peak areas defined manually by placement of two cursors vs. frequency domain curve fitting with the assumption of either Gaussian or Lorentzian line shapes. Large reproducible differences were found in liver metabolite peak areas but not in pH, indicating that processing and peak integration methods can only explain part of the discrepancies between the results from different institutions.

Functional and metabolic analysis of cerebral ischemia using magnetoencephalography and proton magnetic resonance spectroscopy.

The details of the relationship between brain function and metabolism in brain infarcts have not been studied. Using magnetoencephalography (MEG) and proton magnetic resonance spectroscopic imaging (1H MRSI), we localized sources of abnormal magnetic activities in ischemic brain regions and biochemical changes in suspected lesions showing pathological characteristics. Twelve patients with ischemic stroke were examined and the results of MEG and 1H MRSI were superimposed onto the corresponding MR images. The signal intensities of N-acetyl (NA) and lactate (Lac) were measured in the lesions with highly concentrated dipoles of slow wave activity. Eleven of 12 cases had increased slow wave activity in the cortical areas adjacent to the infarcts; 1 case was excluded because the infarct was too small (<1 cm in diameter). The signal intensity of NA in the regions with the highest slow wave activity was significantly reduced and was well correlated with the dipole density of slow waves. Though Lac was mildly accumulated in the lesions, the Lac level had no correlation with slow wave magnetic activity. The remaining and metabolically active cortical tissue showing NA signal produced the abnormal slow wave activity under lactic acidosis (mild accumulation of Lac).

[Cerebral proton spectroscopy of people infected with the human immunodeficiency virus]. / Espectroscopia de protón en el cerebro de personas infectadas por el virus de la inmunodeficiencia humana.

BACKGROUND: This article presents a combined magnetic resonance imaging and proton spectroscopy protocol (MRI/1H-MRS) applied to study the brain of human immunodeficiency virus (HIV) infected patients. The spectroscopic results were compared with clinical and radiological parameters. PATIENTS AND METHODS: The proton spectra of 57 HIV patients and 20 control subjects were obtained from a volume of interest of 8 cm3 located in the parietooccipital region of the brain that did not include any focal lesion. The resonance areas due to N-acetyl aspartate (NAA), creatine (Cr) and choline (Cho) were obtained. The MRI exam allowed us to determine the presence of focal or diffuse lesions and the degree of atrophy. Finally, the clinical exploration included the performance of a Mini-Mental test. The NAA/Cr, NAA/Cho and Cho/Cr ratios were correlated with clinical characteristics, the result of the Mini-Mental test, the presence of lesions and the degree of atrophy. RESULTS: There were altered spectral patterns in a volume of the brain that did not contain any focal lesion. The decrease in the NAA/Cr or NAA/Cho ratios was significative when considering the presence of atrophy, the existence of signs of cognitive deficiencies or the diagnosis of AIDS-dementia complex. CONCLUSIONS: The spectral changes found in the present study suggest the existence of neuronal lesions that would be due to the HIV-infection. A combined MRI/1H-MRS study may provide a more complete information about the neurological impairment by HIV and could constitute a marker of AIDS-dementia complex.

Proton magnetic resonance spectroscopy in patients with glial tumors: a multicenter study.

The authors represent a cooperative group of 15 institutions that examined the feasibility of using metabolic features observed in vivo with 1H-magnetic resonance (MR) spectroscopy to characterize brain tumors of the glial type. The institutions provided blinded, centralized MR spectroscopy data processing long with independent central review of MR spectroscopy voxel placement, composition and contamination by brain, histopathological typing using current World Health Organization criteria, and clinical data. Proton 1H-MR spectroscopy was performed using a spin-echo technique to obtain spectra from 8-cc voxels in the tumor and when feasible in the contralateral brain. Eighty-six cases were assessable, 41 of which had contralateral brain spectra. Glial tumors had significantly elevated intensities of choline signals, decreased intensities of creatine signals, and decreased intensities of N-acetylaspartate compared to brain. Choline signal intensities were highest in astrocytomas and anaplastic astrocytomas, and creatine signal intensities were lowest in glioblastomas. However, whether expressed relative to brain or as intratumoral ratios, these metabolic characteristics exhibited large variations within each subtype of glial tumor. The resulting overlaps precluded diagnostic accuracy in the distinction of low-and high-grade tumors. Although the extent of contamination of the 1H-MR spectroscopy voxel by brain had a marked effect on metabolite concentrations and ratios, selection of cases with minimal contamination did not reduce these overlaps. Thus, each type and grade of tumor is a metabolically hetero-geneous group. Lactate occurred infrequently and in all grades. Mobile lipids, on the other hand, occurred in 41% of high-grade tumors with higher mean amounts found in glioblastomas. This result, coupled with the recent demonstration that intratumoral mobile lipids correlate with microscopic tumor cell necrosis, leads to the hypothesis that mobile lipids observed in vivo in 1H-MR spectroscopy may correlate independently with prognosis of individual patients.

A multicenter proton magnetic resonance spectroscopy study of neurological complications of AIDS.

Human immunodeficiency virus (HIV) infection as seen in Europe and the United States has predominantly been contracted through male homosexual sex or intravenous drug abuse. In infected subjects, the brain is frequently affected both clinically and neuropathologically. The aim of this multicenter study has been to evaluate the value of single-voxel proton magnetic resonance spectroscopy (MRS) in the assessment of the neurological complications of acquired immunodeficiency syndrome (AIDS). MRS (voxel size = 8 ml, TR/TE = 1600/135 msec) was performed in 137 HIV-1-seropositive patients and 64 healthy controls without risk factors at three clinical MR sites operating at 1.5 T. The first result of this multicenter trial is that good reproducibility of results among participating sites was found. This demonstrates the reliability and robustness of MRS in the study of in vivo brain metabolism. In HIV patients, there was no significant correlation between metabolite ratios of brain detected by MRS and CDC grouping of patients or CD4 count. In contrast, the variations of brain metabolite ratios (NA/Cr, NA/Cho, and Cho/Cr) were related to the occurrence of encephalopathy, brain atrophy, or diffuse white matter lesions. There was no significant difference in brain metabolites between male homosexual AIDS patients and male intravenous drug user AIDS patients, whatever their neurological status (neurosymptomatic or neuroasymptomatic). Thus, the mode of transmission of HIV infection does not appear to affect the cerebral changes observed in the proton spectra from AIDS patients. Because of its ease of implementation and high information content, single-voxel proton MRS is likely to play a significant role in the evaluation of HIV-related encephalopathies.

1H MR spectroscopy in patients with metastatic brain tumors: a multicenter study.

In a cooperative study involving six clinical MR centers, localized 1H MR spectroscopy was used to characterize untreated metastatic brain tumors (40 cases, 45 lesions). Cubic volumes (3.4 or 8 cm3) filled for more than 50% by metastatic brain tissue were examined by single-voxel double spin echo MRS, by using chemical shift selective imaging (CHESS) pulses for water suppression and TE = 135 ms. Choline (Cho), creatine (Cr) and N-acetyl aspartate (NAA) levels in brain metastases of mammary carcinoma (n = 13), lung cancer (n = 11) and melanoma (n = 10) were similar. Metastasis NAA/Cho signal intensity ratio varied between 0.00 and 1.17, compared with 2.68 +/- 0.56 (SD) in lobus occipitalis and 1.94 +/- 0.63 in corpus nuclei caudati region (P < 0.0001, both). 1H MR spectroscopy, although not suited to recognize the primary tumor of metastases, could serve as a clinical test for excluding (metastatic) tumor as cause of solitary focal brain disorders that are hard to diagnose with current imaging methods.

[Clinical magnetic resonance spectroscopy: feasibility and methods using whole body tomographs]. / Klinische Magnetresonanzspektroskopie: Möglichkeiten und Methoden an Ganzkörpertomographen.

MR Spectroscopy offers the unique possibility of monitoring the metabolism of various organs non-invasively. Using examples of 1H and 31P MR spectra, experimental and commercially available techniques are presented and evaluated with regard to their potential clinical application. An example of a 1H human brain spectrum with a pathological lactate level illustrates the requirements for MRS examinations in terms of spatial and spectral resolution. STEAM, Spin-Echo, and Chemical Shift Resolved Imaging (CSI) techniques for 1H MRS are compared. In the field of 31P MRS, typical CSI spectra of the brain and liver are presented. First experimental results with a new double-oblique 3D-CSI technique for measurement of PCr/ATP ratios of different anatomical regions of the human heart are shown. The advantages of using double-resonance techniques for Nuclear Overhauser Enhancement (NOE) and decoupling are shown by the example of the phosphodiesters of the liver. The energy metabolism of skeletal muscle under exercise is resolved with 5 sec/spectrum, showing breakdown and synthesis of photocreatine (PCr) and inorganic phosphate (Pi). Appropriate instrumentation and technique are available to many clinics today; great interest now is directed towards the diagnostic value of MRS for certain indications.