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At least 703 records · Page 39Linked to original sources
PubMedDate not supplied

[Magnetic resonance tomography and magnetic resonance angiography in the clinical diagnosis of extra- and intracranial arterial pathology in patients with arterial hypertensions].

The authors analyze diagnostic potentialities of magnetic resonance (MR) angiography of the extra- and intracranial arteries in healthy volunteers and patients with arterial hypertension of various origins and course. Fifteen healthy subjects aged 18 to 40 and 33 patients with arterial hypertension were examined; 13 of these patients presented with essential hypertension, eleven with that combined with extracranial arteries atherosclerosis, and nine with nonspecific aortoartheritic. The most informative images were those of extra- and intracranial arteries in three-dimensional reconstruction making use of programs with a decreased magnetization vector angle and a short TR period when the vessel was characterized by a high intensity of the signal against the background of low-intensive adjacent tissues. MR angiography provides diagnostically reliable information on the status of extra- and intracranial arteries, permits imaging of vascular stenoses and occlusions, as well as of aneurysms and arteriovenous malformations. Analysis of MR angiographic and tomographic data permits a sufficiently accurate assessment of the relationships between MR tomographic picture of the brain and changes in extra- and intracranial arteries. MR angiography extends the potentialities of other MR tomographic methods in assessment of changes in small vessels and helps in a number of cases reduce the number of invasive interventions in examination of a patient.

Adolescent↗
PubMed1993

Heterogeneous metabolic changes in the calf muscle of the rat during ischaemia-reperfusion: in vivo analysis by 31P nuclear magnetic resonance chemical shift imaging and 1H magnetic resonance imaging.

Non-localized and localized 31P nuclear magnetic resonance (NMR) spectra of rat calf muscle during arterial occlusion and after reperfusion were concurrently observed using chemical shift imaging and 1H magnetic resonance imaging (MRI). During ischaemia, the levels of high-energy phosphates (phosphocreatine and adenosine 5'-triphosphate) were depleted and that of inorganic phosphate was increased. In addition, the signal intensity on 1H MRI was increased. These changes were observed to be relatively homogeneous throughout the calf. In contrast, the changes during reperfusion were heterogeneous. In the central part of the calf, inorganic phosphate disappeared, phosphocreatine was restored immediately on reperfusion and the 1H signal was decreased. However, in the regions of the tibialis anterior muscle and the superficial part of the gastrocnemius muscle, inorganic phosphate persisted for several hours, phosphocreatine was not restored and the signal intensity on T2-weighted 1H MRI was increased further. The heterogeneous changes detected by 31P NMR spectroscopy and 1H MRI showed close agreement. The susceptibility of different calf muscles to ischaemia and reperfusion seems to depend on their predominant muscle fibre type (i.e. fast-twitch or slow-twitch fibres). Reversible and irreversible ischaemic changes could be non-invasively distinguished by in vivo 31P NMR spectroscopy and 1H MRI.

Adenosine Triphosphate↗
PubMedDate not supplied

[Neoplasms of the glomus caroticum: magnetic resonance angiography versus magnetic resonance].

This work was aimed at investigating the diagnostic role of Magnetic Resonance angiography (MRA) versus spin-echo images in the study of carotid paragangliomas. Ten patients affected with carotid paragangliomas were studied; surgery was the gold standard. MR examinations were performed with a superconductive 1.5 T magnet and a linear head coil. T1-weighted (TR 500 ms, TE 15 ms, 256 x 256 matrix) and T2-weighted (TR 2000 ms, TE 15/90 ms, 256 x 256 matrix) spin-echo sequences were acquired. TOF 3D (flash: FA 25 degrees, TR 30 ms, TE 7 ms) MRA images were acquired; coronal and sagittal images were rotated according to the MIP. Spin-echo images demonstrated the typical "salt and pepper" pattern in all cases. In 6 cases (lesion diameter > 3 cm) the vascular structures of the paragangliomas and carotid dislocation were clearly demonstrated by MRA. MRA also depicted carotid dislocation in all cases. In conclusion, in the evaluation of carotid paragangliomas > 3 cm diameter, MRA yields complementary information on vascular structures and dislocation of carotid vessels to spin-echo MR sequences.

Adult↗
PubMed1994

Magnetic resonance angiography compared with basic magnetic resonance in intracranial vascular diseases.

The diagnostic value of magnetic resonance angiography (MR-Angio) in the study of intracranial vascular diseases was compared with that of basic magnetic resonance (MR) in 35 patients presenting with a total of 45 pathologies (13 vascular malformations, 17 aneurysms, 3 vascular stenoses, all also examined by standard angiography, and 12 cases of dolichobasilar artery). A joint reading of the results was carried out by two radiologists who evaluated the basic MR and MR-Angio separately and thereafter filled in a fixed-choice answer form. In the author's opinion, MR-Angio may be considered a complementary technique to basic MR, offering a greater capacity for identification and characterization of these intracranial lesions. In vascular malformations and aneurysms, MR-Angio may be performed as a preliminary to digital subtraction angiography.

Aneurysm↗
PubMed1994

Magnetic field strength issues in magnetic resonance imaging.

The authors review the current status of magnetic resonance imaging (MRI) with respect to magnetic field strength. The discussion covers the practical aspects of MRI--safety, throughput and costs--as well as the clinical aspects as they are influenced by field strength. Data on the world distribution of MRI units of various field strengths are presented. Canada had the highest proportion of high-field units among the 11 countries or regions included in this comparison, probably because most Canadian MRI units are located in teaching hospitals, where they are used for both research and clinical work.

Costs and Cost Analysis↗
PubMed1993

[Angiography with magnetic resonance of the ++carotid arteries. Evaluation of clinical results obtained with low magnetic field equipment].

Magnetic Resonance Angiography (MRA) is the latest diagnostic technique for the noninvasive evaluation of cardiovascular conditions. This technique has proved to be especially useful in the study of carotid arteries. All the clinical studies reported to date have been obtained at high or medium field strength; our purpose is to assess the clinical value of MRA in the evaluation of carotid arteries at low field strength. All the exams were performed with an 0.2 T permanent magnet, using the 2D time of flight (TOF) technique, the only one which is currently available on our equipment. Forty-two patients with clinical diagnosis of cerebrovascular insufficiency were examined. In all cases MRA findings were confirmed with digital subtraction angiography (DSA), which was considered the gold standard. The double-blind evaluation of the results showed high agreement of the two techniques in 70 of 84 carotid arteries. A mild tendency to overestimation was observed in 4 normal cases considered as mild stenoses on MRA, in 2 cases with mild stenosis considered as discrete stenoses on MRA and in 1 case of severe stenosis considered as an occlusion on MRA. Underestimation was seen in 1 case of mild stenosis considered as normal on MRA, in 2 cases of discrete stenosis which appeared as mild stenoses on MRA and in 2 cases of occlusion considered as severe stenoses. Our study showed high agreement between MRA and DSA results, which means that high quality exams can be obtained even at low field strength. Further progress can be expected when 3D TOF and phase-contrast techniques will be introduced.

Adult↗
PubMedDate not supplied

[The contrast enhancement of brain and spinal cord tumors using Gd-DTPA in magnetic resonance tomography with an extra-low magnetic-field intensity].

The contrasting agent Gd-DTPA (Magnevist, Schering AG, Germany) was tested when used in magnetic resonance tomography using extra-low (0.04 T) magnetic field intensity in 68 patients with various brain and spine tumors. The agent was injected intravenously in a dose of 0.1 mmol/kg. No complications were found. The tests showed its high efficiency in the diagnosis of brain neoplasms (particularly in malignant intracerebral disorders, meningiomas and neurinomas). Benign astrocytomas induced no noticeable signal intensification on post-contrasting T1-weighed tomograms. In all cases of spinal tumors, the application of Gd-DTPA could specify the extent of tumor invasions, the presence of cysts and identify accessory tumor nodes in one case.

Adult↗
PubMed1993

[A case of cavernous angioma--usefulness of magnetic resonance imaging and magnetic resonance angiography in diagnosis].

We reported a case of cavernous angioma in the middle cranial fossa, which was diagnosed with magnetic resonance imaging (MRI) and magnetic resonance angiography (MRA). The patient was a 56-year-old female, who presented with sudden onset right-sided headache with nausea. Her neurological findings were normal. On CT scan a high density area with a surrounding thin low density area was shown in the right posterior temporal region without contrast enhancement. Cerebral angiography of the left vertebral artery revealed only a small stain at the end of the right posterior temporal artery. On T2-weighted MRI after one month, the same region exhibited a central area of mixed signal intensities surrounded by a rim of decreased signal. MRA showed an area with remarkable 10mm mass with some contiguous vessels in the right posterior temporal region. That mass was resected operatively. It's pathological diagnosis was cavernous angioma. For diagnose of cavernous angioma, MRI and MRA were very useful. The specificity of these methods are superior to better than CT or angiography.

Brain Neoplasms↗
PubMed1996

[Studies on transcranial magnetic stimulation--characteristics of the magnetic coil].

I measured the characteristics of several different magnetic coils. In a round coil and a doughnut-shaped coil, induced voltages measured by a longitudinal probe and compound muscle action potentials (CMAPs) recorded from the abductor pollicis brevis showed two peak voltages in the former at a point halfway between the coil center and the outer edge, and in the center of the windings in the latter. On the other hand, in a double coil, the maximum induced voltage showed a peak at the center of the coil, and when the coil current was antidromically charged against the median nerve, the distribution of CMAPs was more focal. When the distance from the coil surface was disregarded, the maximum induced voltage spot in the double coil did not move. However, in the other coils, it moved closer to the outer edge. From these findings, it was confirmed that a double coil is the most suitable for focal stimuli. In conclusion, when using magnetic coils, the peak spot of various coils and the direction of the coil current against the target nerve are important.

Action Potentials↗
PubMedDate not supplied

[Potential mechanism of therapeutic effect of magnetic effect of magnetic field and photic stimulation on the nerve fibers in the visual tract].

Constant and alternating external magnetic fields induce a sedative effect due to Lorentz forces and also stimulate indirectly metabolic processes. With the properly chosen polarity of the inductor and its position relative to nerve fibers, and with asymmetric and inhomogeneous electrical conductivity in the vicinity of excited fibers, which can be enhanced by pattern light stimulation, magnetic fields produced by asymmetric impulses with one steep front (fore and back) can further enhance excitability and conductivity.

Humans↗
PubMedDate not supplied

[3 Tesla magnetic resonance imaging of the brain. Better morphological and functional images with higher magnetic field strength].

3T MRI offers improved morphological and functional studies of the brain compared with the more commonly used field strength 1.5T. Clinical 3T MRI of the brain is beneficial for high resolution morphological imaging, MR angiography, diffusion-MRI including diffusion tensor imaging, perfusion-MRI, functional MRI (fMRI), and MR spectroscopy. The performance is enhanced by the combination with powerful magnetic field gradients.

Brain↗
PubMedDate not supplied

Tyrosinemia: computed tomography, magnetic resonance imaging, diffusion magnetic resonance imaging, and proton spectroscopy findings in the brain.

In a 5-month-old boy with tyrosinemia, computed tomography revealed diffuse hypodensity in the centrum semiovale. Magnetic resonance (MR) imaging revealed partial signal differences in the white matter and perirolandic regions, and the posterior limbs of the internal capsules revealed higher signal compared with the remainder of the white matter. There were high-signal changes (restricted water diffusion) in the corresponding regions on images of diffusion-weighted MR imaging (b = 1000 s/mm). This likely represented the presence of intramyelinic edema attributable to status spongiosus. Proton MR spectroscopy (repetition time = 1500 milliseconds, echo time = 40 milliseconds) from the lesion sites revealed 2 separate prominent peaks spread between 3.4 and 3.9 ppm. These peaks could represent the CH and CH2 aliphatic protons of the tyrosine molecule.

Brain↗
PubMed2007

Effects of 3d-4f magnetic exchange interactions on the dynamics of the magnetization of Dy(III)-M(II)-Dy(III) trinuclear clusters.

[{Dy(hfac)(3)}(2){Fe(bpca)(2)}] x CHCl(3) ([Dy(2)Fe]) and [{Dy(hfac)(3)}(2){Ni(bpca)(2)}]CHCl(3) ([Dy(2)Ni]) (in which hfac(-)=1,1,1,5,5,5-hexafluoroacetylacetonate and bpca(-)=bis(2-pyridylcarbonyl)amine anion) were synthesized and characterized. Single-crystal X-ray diffraction shows that [Dy(2)Fe] and [Dy(2)Ni] are linear trinuclear complexes. Static magnetic susceptibility measurements reveal a weak ferromagnetic exchange interaction between Ni(II) and Dy(III) ions in [Dy(2)Ni], whereas the use of the diamagnetic Fe(II) ion leads to the absence of magnetic exchange interaction in [Dy(2)Fe]. Dynamic susceptibility measurements show a thermally activated behavior with the energy barrier of 9.7 and 4.9 K for the [Dy(2)Fe] and [Dy(2)Ni] complexes, respectively. A surprising negative effect of the ferromagnetic exchange interaction has been found and has been attributed to the structural conformation of these trinuclear complexes.

Journal Article↗
PubMed2001

Breathhold unenhanced and gadolinium-enhanced magnetic resonance tomography and magnetic resonance cholangiography in hilar cholangiocarcinoma.

We assessed the imaging characteristics of hilar cholangiocarcinoma in magnetic resonance imaging (MRI) and magnetic resonance cholangiography (MRC). Breathhold MRI (T2-weighted turbo spin echo sequences, unenhanced T1-weighted gradient echo sequences, and gadolinium-enhanced fat-suppressed gradient echo sequences) and breathhold MRC (fat-suppressed two-dimensional projection images) performed in 12 patients with histologically confirmed hilar cholangiocarcinoma were retrospectively reviewed for morphological tumor characteristics and contrast enhancement patterns. MRC demonstrated a significant bile duct stenosis with intrahepatic bile duct dilatation in all cases except in one patient who received an endoprothesis prior to imaging. Hilar cholangiocarcinoma was diagnosed by MRC only in one patient and MRI and MRC in 11. Mass lesions were seen in nine patients and circumferential tumor growth in three, including the patient diagnosed by MRC only. The tumor appeared hypointense relative to liver parenchyma in 10 of 11 patients in unenhanced T1-weighted images. T2-weighted sequences showed isointense or only slightly hyperintense signal in 5 of 11 patients, 3 of whom demonstrated desmoplastic reactions by histology. The other 6 patients revealed strongly hyperintense signal intensities. Contrast enhancement was increased compared to liver in 5 of 11 patients and decreased in 6 of 11 patients. MRI with MRC seem to be a sensitive tools in the detection of hilar cholangiocarcinomas. The variable imaging characteristics are most probably related to the inhomogeneous histological appearance of this tumor entity.

Aged↗
PubMed2005

Exposure of postnatal rats to a static magnetic field of 0.14 T influences functional laterality of the hippocampal high-affinity choline uptake system in adulthood; in vitro test with magnetic nanoparticles.

Our previous experiments indicated an age- and sex-dependent functional lateralization of a high-affinity choline uptake system in hippocampi of Wistar rats. The system is connected with acetylcholine synthesis and also plays a role in spatial navigation. The current study demonstrates that a single in vivo exposure of 7- or 14-day-old males to a static magnetic field of 0.14 T for 60-120 min evokes asymmetric alterations in the activity of carriers in adulthood. Namely, the negative field (antiparallel orientation with a vertical component of the geomagnetic field) mediated a more marked decrease in the right hippocampus. The positive field (parallel orientation) was ineffective. Moreover, differences between the carriers from the right and the left hippocampi were observed on synaptosomes pretreated with superparamagnetic nanoparticles and exposed for 30 min in vitro. The positive field enhanced more markedly the activity of carriers from the right hippocampus, the negative that from the left hippocampus, on the contrary. Our results demonstrate functionally teratogenic risks of the alterations in the orientation of the strong static magnetic field for postnatal brain development and suggest functional specialization of both hippocampi in rats. Choline carriers could be involved as secondary receptors in magnetoreception through direct effects of geomagnetic field on intracellular magnetite crystals and nanoparticles applied in vivo should be a useful tool to evaluate magnetoreception in future research.

Aging↗
PubMed1984

Low temperature magnetic circular dichroism spectra and magnetization properties of extracted heme a3+ bis-imidazole. A model of cytochrome a in bovine cytochrome c oxidase.

Heme a3+ isolated from bovine cardiac muscle cytochrome oxidase has been converted to the bis-imidazole species and studied by magnetic circular dichroism (MCD) spectroscopy. Spectra have been recorded down to 1.5 degrees K, enabling the MCD magnetization curves to be measured at a number of wavelengths in the visible and near infrared regions. The experimentally determined curves show excellent correlation to a curve using the g-values determined by electron paramagnetic resonance spectroscopy to be gz = 2.96, gy = 2.29, and gx = 1.73. The data show that the bis-imidazole derivative of extracted heme a3+ is an excellent model of cytochrome a in the enzyme, confirming the presence of two histidine residues in the protein as the fifth and sixth ligands. The spectral features of heme a3+ bis-imidazole in the near infrared region are consistent with transitions of the porphyrin ( a1u , a2u ) to ferric (eg) charge transfer type.

Animals↗