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PubMedDate not supplied

[The interactions between metal stapes prostheses and high-intensity magnetic fields during magnetic resonance tomography].

The ever-increasing use of magnetic resonance tomography (MR) as an investigation mean has created a new interest in the biological effects of magnetic fields (MF) and in finding protective measures to be taken in their event. At the moment, use of MR is contraindicated in the presence of pacemakers, vascular clips, liquoral shunts and orthopedic prostheses, all of which may be dislocated by the MF created by MR or may interact with the MF itself creating distorted or falsified images. The aim of our study was to verify if metallic stapedectomy prostheses are dislocated by the MF and if they produce enough interference to falsify MR images. Five types of metallic stapedial prostheses exposed to a MF of 0.5T were studied. We may conclude from our results that MR does not create any otological risks for patients with these prostheses in that none of them were dislocated during exposure. However, all the prostheses studied did instead bring about alterations in the MF and the MR image to varying degrees. In some cases (Robinson) there was notable image distortion, while in others (Schuknecht wire teflon and platinum piston) the distortion was practically negligible. It is our opinion, however, that even if the image distortion does not interfere with routine MR, use of prostheses made of materials not affected by MF are advisable in view of an eventual development of visualization of the labyrinth and intratemporal facial nerve portion with MR.

Artifacts↗
PubMedDate not supplied

[Monitoring of pediatric patients undergoing magnetic resonance diagnosis with a superconducting magnet].

Magnetic resonance imaging (MRI) has presented to anesthesiologists as unique challenge in patient monitoring because of its construction and principles of operation. Ferromagnetic materials within or near the scanner can distort the magnetic field, and monitoring wires act as antennae and this may result in image degradation. Nevertheless, monitoring is mandatory during MRI, especially in a child sedated or in general anesthesia. A monitoring system, made up of commercially available components, was assessed, and its effects on MR (1.5 tesla unit) image quality system determined. Variables monitored included: electrocardiogram and heart rate, (Sirecust 404, ECG cable set MR; Siemens, Enlanger, West Germany); blood pressure via automated sphygmomanometry (Press Mate BP-8800; Colin, Komaki, Japan); and continuous arterial saturation via pulse oximetry (Nellcor 100 E; Nellcor, Inc., Haywood, California). Fluid infusion rate was controlled by means of a plastic deliver (Dial-a-flo; Abbott Labs., Chicago, Illinois). Body temperature was maintained with a heat insulator blanket (Thermadrape, OR Concepts, Inc., Dallas, Texas). The monitoring technique described did not interfere with MRI function or produce image degradation.

Anesthesia↗
PubMed1990

[Monitoring of an acute compartment syndrome of unusual etiology using MRI (magnetic resonance tomography) and MRS (magnetic resonance spectroscopy)].

The authors report on an acute compartment syndrome occurring symmetrically in the extensors of both forearms. The etiology of this unique compartment syndrome, not previously described, could be attributed to the inhalation of a propane-butane gas mixture, low in oxygen, while sleeping, in combination with external compression of both forearms, due to the patient's head lying on both forearms while sleeping. Ischemic damage to muscles was precisely located using non-invasive MRI (Magnetic Resonance Imaging). The extent of cellular damage due to ischemia after fasciotomy and healing by secondary intention was quantitatively assessed using non-invasive 31P-MRS (Phosphorus Magnetic Resonance Spectroscopy). The results correlate with the clinical and histological findings and indicate a bioenergetic regeneration of the ischemic skeletal muscle's cells.

Adult↗
PubMed1986

Combined magnetic resonance imaging and bihemispheric magnetic resonance spectroscopy in acute experimental focal cerebral ischemia.

Combined magnetic resonance imaging (MRI) and 31P-magnetic resonance spectroscopy (MRS) were employed to evaluate acute regional cerebral ischemia in cats following middle cerebral artery occlusion (MCAO). MRI changes were first reliable 3 hours after MCAO; progressive increases in T1 and T2 relaxation times were noted for 12 hours after MCAO. Immediately after MCAO, 31P-MRS revealed decreased phosphocreatine (PCr) and increased inorganic phosphate (Pi); the PCr/Pi ratio fell from 2.23 +/- 0.40 to 0.68 +/- 0.04 (p less than 0.005). This relative decrease in high energy phosphates improved significantly by 3-5 hours after MCAO (0.67 +/- 0.04 versus 1.00 +/- 0.03, p less than 0.001). By 12 hours, the ratio had increased by 27 per cent. The dissociation between the progressive MRI changes and the gradual improvement in 31P-MRS suggests a difference between the processes affecting proton distribution and phosphate metabolism in acute regional ischemia.

Acute Disease↗
PubMed1994

Ultrafast magnetic resonance imaging. Segmented turboflash, echo-planar, and real-time nuclear magnetic resonance.

Ultrafast magnetic resonance imaging refers to a group of techniques developed with the sole purpose of acquiring images in a very rapid fashion. Ultrafast magnetic resonance imaging has other benefits besides capture of transient events. Not all patients have a stable heart rate, and many cannot tolerate remaining still and breathing quietly for long periods while lying inside of a scanner. Fast imaging reliably acquires data, even if the patient moves or is arrhythmic. This article describes strategies, applications, advantages, and limitations of ultrafast imaging.

Computer Systems↗
PubMed1997

Magnetic resonance imaging volumetric and phosphorus 31 magnetic resonance spectroscopy measurements in schizophrenia.

The purpose of this study was to examine the relationship between phosphorus magnetic resonance spectroscopy (31P MRS) parameters and left prefrontal volumes in both patients with schizophrenia and healthy subjects. 31P MRS parameters and magnetic resonance imaging (MRI) volumetric data were collected in the left prefrontal region in 10 patients with schizophrenia and 10 healthy subjects of comparable age, handedness, sex, educational level, and parental educational level. No correlations were found between any MRS parameter and grey matter volumes in the combined subjects. Phosphomonoester (PME) and grey matter volumes, however, were both correlated negatively with age. PMEs were found to be decreased, and calculated intracellular magnesium ([Mg2+]intra) was found to be increased in the patients with schizophrenia compared with healthy subjects after adjusting for left prefrontal grey and white matter, total brain volume, and age. These findings suggest that cortical grey and white manner volumes are not directly related to PME and [Mg2+]intra abnormalities in schizophrenia patients.

Adult↗
PubMed2000

Advantages of adding diffusion-weighted magnetic resonance imaging to conventional magnetic resonance imaging for evaluating acute stroke.

BACKGROUND: Accurate localization of acute ischemic lesions in patients with an acute stroke may aid in understanding the etiology of their stroke and may improve the management of these patients. OBJECTIVE: To determine the yield of adding diffusion-weighted magnetic resonance imaging (DWI) to a conventional magnetic resonance imaging (MRI) protocol for acute stroke. DESIGN: A prospective cohort study. SETTING: A referral center. PATIENTS AND METHODS: Fifty-two patients with a clinical diagnosis of acute stroke who presented within 48 hours after symptom onset were included. An MRI scan was obtained within 48 hours after symptom onset. A neuroradiologist (A.M.N.) and a stroke neurologist (G.W.A.) independently identified suspected acute ischemic lesions on MRI sequences in the following order: (1) T2-weighted and proton density-weighted images, (2) fluid-attenuated inversion recovery images, and (3) diffusion-weighted images and apparent diffusion coefficient maps. MAIN OUTCOME MEASURES: Diagnostic yield and interrater reliability for the identification of acute lesions, and confidence and conspicuity ratings of acute lesions for different MRI sequences. RESULTS: Conventional MRI correctly identified at least one acute lesion in 71% (34/48) to 80% (39/49) of patients who had an acute stroke; with the addition of DWI, this percentage increased to 94% (46/49) (P<.001). Conventional MRI showed only moderate sensitivity (50%-60%) and specificity (49%-69%) compared with a "criterion standard." Based on the diffusion-weighted sequence, interrater reliability for identifying acute lesions was moderate for conventional MRI (kappa = 0.5-0.6) and good for DWI (kappa = 0.8). The observers' confidence with which lesions were rated as acute and the lesion conspicuity was significantly (P<.01) higher for DWI than for conventional MRI. CONCLUSION: During the first 48 hours after symptom onset, the addition of DWI to conventional MRI improves the accuracy of identifying acute ischemic brain lesions in patients who experienced a stroke.

Acute Disease↗
PubMed2004

European study on intravenous immunoglobulin in multiple sclerosis: results of magnetization transfer magnetic resonance imaging analysis.

BACKGROUND: Magnetization transfer magnetic resonance imaging (MT MRI) can provide in vivo markers reflecting the severity of multiple sclerosis-related brain damage occurring within and outside T2-visible lesions. OBJECTIVE: To investigate the effect of intravenous immunoglobulin (IVIG) treatment on the accumulation of brain damage in patients with secondary progressive multiple sclerosis (SPMS), measured using MT MRI.Design, Patients, and Intervention Seventy patients with SPMS participating in the European, multicenter, randomized, double-blind, placebo-controlled trial of IVIG in SPMS underwent brain T2-weighted and MT MRI at baseline and after 12 and 24 months. The MT MRI scans were post-processed and analyzed to obtain MT ratio values from T2-visible lesions and MT ratio histograms from the normal-appearing brain tissue (NABT). RESULTS: At baseline, a significant difference was found for NABT MT ratio histogram peak height (P =.003) between treated patients and patients receiving placebo. No significant differences between treated patients and those receiving placebo were found for any of the considered MT MRI-derived metrics in terms of treatment x time interaction. Nevertheless, over the 24-month period, the placebo patients experienced a 6.75% reduction of the NABT MT ratio histogram peak height, whereas treated patients experienced only a 0.92% reduction of the NABT MT ratio histogram peak height. CONCLUSIONS: This study did not show any statistically significant effect of IVIG on MT MRI quantities. Nevertheless, the markedly different percentage change of the NABT MT ratio histogram peak height over time between patients receiving placebo and treated patients suggests a possible role of IVIG treatment in preventing the loss of "truly" normal brain tissue in SPMS patients.

Brain↗
PubMed2006

Magnetization transfer magnetic resonance imaging and clinical changes in patients with relapsing-remitting multiple sclerosis.

BACKGROUND: Magnetization transfer (MT) magnetic resonance imaging (MRI) can provide in vivo quantitative estimates of microscopic tissue damage in normal-appearing white matter (NAWM) and gray matter (GM) from patients with multiple sclerosis (MS). OBJECTIVE: To determine whether a one-time MT MRI can provide markers of short-term disease evolution in patients with relapsing-remitting MS. DESIGN: Eighteen-month observational study. SETTING: Neuroimaging Research Unit, Scientific Institute and University Ospedale San Raffaele. PATIENTS: Twenty-two patients with untreated relapsing-remitting MS. MAIN OUTCOME MEASURES: Relapse rate; disability according to the Expanded Disability Status Scale (EDSS); dual-echo, 2-dimensional gradient echo with and without a saturation MT pulse and T1-weighted MRIs of the brain; and MT ratio (MTR) histograms for NAWM and GM. RESULTS: During the study period, 13 patients (59%) experienced 25 relapses. The median EDSS score was 1.25 (range, 0-3.5) at study entry and 1.75 (range, 0-3) at study exit. Significant, although moderate, correlations were found between average GM MTR values at baseline and EDSS changes during the study period (r = -0.44; P = .04). A trend was observed for the correlation between NAWM MTR values at baseline and the EDSS changes throughout 18 months (r = -0.42; P = .05). For the relation between EDSS changes and baseline GM MTR, the slope of the regression line was -0.5 (95% confidence interval, -1.0 to 0.0), indicating that a decrease in the baseline GM MTR of 1% predicted an increase in the EDSS score of 0.5 point throughout the 18 months. CONCLUSION: This study indicates that a "snapshot" MT MRI assessment detects subtle brain tissue changes that are associated with short-term disability accumulation in patients with relapsing-remitting MS.

Adult↗
PubMed2002

Preparation of luciferase-bacterial magnetic particle complex by artificial integration of MagA-luciferase fusion protein into the bacterial magnetic particle membrane.

MagA is an iron-translocating protein found in the membranes of magnetic bacterium. Luciferase-bacterial magnetic particle (BMP) complexes were prepared by artificially inserting MagA-luciferase fusion proteins into the membranes of BMPs from Magnetospirillum magneticum strain AMB-1. Fusion proteins were from recombinant Escherichia coli membranes. MagA-Luc fusion proteins were integrated by sonication in vitro. Successful integration of fusion proteins was confirmed by luciferase luminescence on BMPs. Maximum luminescence was obtained after sonication for 3 min with a solution containing 300 mM NaCl, and is 18 times higher compared with recombinant Luc-BMPs generated using previously reported gene fusion techniques.

Artificial Gene Fusion↗
PubMed2004

Musical training-induced functional reorganization of the adult brain: functional magnetic resonance imaging and transcranial magnetic stimulation study on amateur string players.

We used the combined technique of functional magnetic resonance imaging (fMRI) and transcranial magnetic stimulation (TMS) to observe changes that occur in adult brains after the practice of stringed musical instruments. We carried out fMRI on eight volunteers (aged 20-22 years): five novices and three individuals who had discontinued practice for more than 5 years. The motor paradigm contained a repetitive lift-abduction/fall-adduction movement of the left/right little finger, carried out with maximum efforts without pacing. The sensory paradigm was to stimulate the same little finger using a string. In parallel to the fMRI acquisition, TMS motor maps for the little finger were obtained using a frameless stereotactic neuronavigation system. After the baseline study, each participant began to learn a stringed instrument. Newly developed fMRI activations for the left little finger were observed 6 months after practice at multiple brain regions including inferior parietal lobule, premotor area (PMA), left precuneus, right anterior superior temporal gyrus, and posterior middle temporal gyrus. In contrast, new activations were rarely observed for the right little finger. The TMS study revealed new motor representation sites for the left little finger in the PMA or supplementary motor area (SMA). Unexpectedly, TMS motor maps for the right little finger were reduced significantly. Among new fMRI activations for sensory stimuli of the left little finger, the cluster of highest activation was located in the SMA. Collectively, these data provide insight into orchestrated reorganization of the sensorimotor and temporal association cortices contributing to the skillful fingering and musical processing after the practice of playing stringed instruments.

Adult↗
PubMed1994

Blood-brain barrier permeability in rats is altered by exposure to magnetic fields associated with magnetic resonance imaging at 1.5 T.

We have previously reported that exposure of rats to low-field (0.15 T) magnetic resonance imaging (MRI) increases blood-brain barrier (BBB) permeability. However, a number of investigators have failed to observe this effect when high-field MRI (1.5 T or higher) is used. Therefore, we investigated whether or not we would observe changes using our technique at these higher fields. Adult male Sprague-Dawley rats were anaesthetised and then exposed to a 22.5 min imaging or sham procedure. Immediately following exposure, rats were injected with 1 MBq of 153Gd-DTPA intracardially and then immediately re-exposed for an additional 22.5 min. The rats were killed 1h following the second MRI exposure, at which time the brain was resected and 3 ml of venous blood collected. The ratio of radioactivity per gram of brain to radioactivity per milliliter of blood, known as the brain-blood partition coefficient, was determined and used as a measure of BBB permeability. Groups of animals had different exposures. Group 1 (n = 9) was exposed to a clinically relevant MRI procedure. Group 2 (n = 20) was exposed to the same procedure except the rf specific absorption rate (SAR) was reduced to 25% and the animals were positioned 15 cm from imager centre to increase the time-varying magnetic field from 0.4 to 2.8 T/s. For the sham exposures (n = 21), the animals were placed in the imager with the static field ramped down to zero and exposed to a sound recording simulating a MRI examination.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2004

Off-axis electron holography of magnetic nanowires and chains, rings, and planar arrays of magnetic nanoparticles.

A selection of recent results illustrating the application of off-axis electron holography to the study of magnetic microstructure in closely-spaced nanoparticles and nanowires is reviewed. Examples are taken from the characterization of FeNi nanoparticle chains, Co nanoparticle rings, two-dimensional arrays of naturally occurring magnetite crystals in minerals, and single crystalline Co nanowires. Approaches that can be used to separate the magnetic signal of interest from the mean inner potential contribution to the measured holographic phase shift are described, and the spatial and phase resolution that can be achieved are discussed.

Algorithms↗
PubMed2003

Guidelines for using quantitative magnetization transfer magnetic resonance imaging for monitoring treatment of multiple sclerosis.

Quantitative evaluation of brain magnetic resonance imaging (MRI) scans is now an accepted part of the trial of new putative treatments for multiple sclerosis (MS). However, conventional MRI is not pathologically specific, and it does not reveal the details of the pathological processes that underlie the progression of the disease. Magnetization transfer (MT) imaging is a relatively new quantitative technique that appears to offer some pathological specificity, and can be used to monitor the changes over time in both individual lesions and the central nervous system as a whole. This paper considers the case for incorporating MT imaging into new clinical trials, so that the utility of MT for monitoring the modification of MS progression by treatment can be assessed. Specific guidelines for implementing MT imaging as part of a large multicenter clinical trial are given, and practical considerations when planning such a trial are detailed. It is anticipated that MT imaging will be incorporated into many new trials in the near future.

Brain↗
PubMed2003

Indirect imaging of ethanol via magnetization transfer at high and low magnetic fields.

Ethanol (EtOH) is believed to exert its neurochemical effects through interactions with brain cellular components, which causes a fraction of brain EtOH to have a lower molecular mobility. This facilitates magnetization transfer to other molecules similarly associated with macromolecules, such as water. It was hypothesized that this effect can be used in vivo to image EtOH indirectly via the much stronger brain tissue water resonance. EtOH-containing bovine serum albumin samples were used to demonstrate magnetic coupling between EtOH and water at 7 T and 1.5 T. Spectroscopy and imaging experiments demonstrated that EtOH signal saturation yielded greater water signal reduction than inversion and that this reduction scaled with EtOH concentration in the BSA samples. In human brain at physiologically relevant brain EtOH concentrations, water signal reductions were measurable when saturating the EtOH resonance. Strengths and limitations of indirectly imaging brain EtOH are discussed.

Brain↗
PubMed2001

Nuclear magnetic relaxation dispersion of ferritin and ferritin-like magnetic particle solutions: a pH-effect study.

The relaxation mechanism of water protons in the presence of ferritin is still being debated. In this work, the pH dependence of the relaxation induced by ferritin and Fercayl, a ferritin-like akaganeite particle, is studied through T1 and T2 nuclear magnetic relaxation dispersion (NMRD) profiles. To differing extents, the relaxation brought about by both systems is significantly affected by pH. A proton exchange time of 33 ns (at pH 6 and 37 degrees C) is deduced from the fittings of Fercayl T1 NMRD profiles. The linearity of the relationship between 1/T2 and the magnetic field B0 for ferritin and Fercayl solutions is not altered by changes in pH. The parameters of this linearity strongly depend on pH for the latter, while remaining unchanged for the former. These results are interpreted in terms of an exchange between protons belonging to hydroxyl groups at the surface of the particle and bulk water protons.

Animals↗
PubMed1996

Power efficient on-resonance saturation pulses for magnetization transfer in magnetic resonance imaging.

A family of new on-resonance saturation pulses for magnetization transfer in MRI is proposed. These pulses can be represented as a product of a shaped function and a cosine function. The shaped function can have many different forms, one of which is a Gaussian function. The experimental results on a 1.0 T whole body scanner show that the new on-resonance pulses are more efficient for magnetization transfer than either on-resonance binomial sequence pulses or off-resonance Gaussian pulses at the same power level.

Humans↗
PubMed1998

Recording of electrical brain activity in a magnetic resonance environment: distorting effects of the static magnetic field.

The technical limitations of electroencephalography (EEG) and flashed visually-evoked potentials (VEP) recordings in the static magnetic field of the MR system were systematically studied. A main artifact occurring in the magnetic field was found to be correlated with the heart cycle and had amplitudes in the range of EEG and VEP signals. For VEP recordings, a substantial reduction of this effect was achieved by subtraction of the averaged artifact from the averaged composed signal (VEP and artifact) resulting in the VEP signal alone. However, for continuous EEG recordings, there is no such solution, since the observed effect is not sufficiently constant in amplitude, and the standard deviation of the amplitude of the effect is often larger than the EEG amplitude.

Artifacts↗