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At least 235 records · Page 13Linked to original sources
PubMed1997

Use of magnetic resonance imaging and magnetic resonance angiography in diagnosis of sigmoid sinus thrombosis.

Magnetic resonance angiography is an established radiologic technique which is rapidly becoming useful in imaging the head and neck. Currently, this imaging modality is important in the diagnosis of sigmoid sinus thrombosis caused by otologic disease. Since the introduction of antibiotic therapy, the percentage of deaths attributed to intracranial complications from otitic disease has decreased from 2.5 to approximately 0.25% of documented deaths. Also, the incidence of sinus thrombosis within this group has decreased, but it is still a serious and potentially lethal condition. Sinus thrombosis is suspected clinically when mastoid disease progresses, with picket fence fever pattern, chills, headaches and signs of papilledema. Definitive diagnosis is necessary before surgical treatment. The Queckenstedt test is unreliable, computed tomography is better suited for demonstrating thrombosis of the sagittal sinus rather than the sigmoid sinus, and conventional angiography (although it provides excellent visualization) has the hazard of ionizing radiation and requires vessel puncture and the use of intraarterial contrast agents. We present two cases of thrombosis of the sigmoid sinus as an intracranial otologic complication which were diagnosed definitively with magnetic resonance imaging and magnetic resonance angiography. The combination of magnetic resonance imaging, which showed the thrombosis displaying abnormal signal intensity, and magnetic resonance angiography, which demonstrated the absence of flow in the sinus, was an ideal diagnostic tool. For both patients, treatment consisted of mastoidectomy, sigmoid sinus decompression and antibiotics.

Adolescent↗
PubMed1995

Assessment of ganciclovir toxicity to experimental intracranial gliomas following recombinant adenoviral-mediated transfer of the herpes simplex virus thymidine kinase gene by magnetic resonance imaging and proton magnetic resonance spectroscopy.

Magnetic resonance imaging and in vivo localized H magnetic resonance spectroscopy were used to evaluate a gene therapy approach for treating experimental brain tumors. This approach involved the use of an adenoviral vector to transfer the herpes simplex virus thymidine kinase (HSVtk) gene into intracerebral 9L gliosarcomas in rats followed by systemic administration of the antiherpetic agent ganciclovir. Magnetic resonance imaging quantitation of changes in intracranial 9L tumor doubling times revealed a significant variation in therapeutic response. Localized H magnetic resonance spectra of 9L tumors treated with Ad.RSVtk/ganciclovir revealed a dramatic increase in the resonance intensity at 0.9-1.3 ppm, corresponding to mobile lipids and/or lactate. Changes in intracranial tumor doubling times correlated with changes in H tumor magnetic resonance spectra, suggesting that specific changes in tumor metabolite levels may be predictive of the effectiveness of this gene therapy approach.

Animals↗
PubMed1994

Clinical diagnosis of multiple sclerosis. The impact of magnetic resonance imaging and ancillary testing. Rochester-Toronto Magnetic Resonance Study Group.

OBJECTIVE: Magnetic resonance imaging, computed tomography, cerebrospinal fluid analysis, and evoked potential testing are used to assist in the diagnosis of patients suspected to have multiple sclerosis (MS). The impact of these tests on a clinician's diagnosis of patients suspected to have MS has not been studied systematically. DESIGN: Clinicians made a diagnosis of each patient following clinical evaluation, again after reviewing the results of magnetic resonance imaging, and finally after reviewing information from other laboratory testing. These diagnoses were compared with the criterion standard of a masked "gold standard" panel reviewing all information after a mean follow-up of 0.9 year. SETTING: The General Neurology Clinic and Multiple Sclerosis Clinic of the University of Rochester (NY). PATIENTS: A consecutive sample of 62 patients diagnosed as having either possible or probable MS following clinical evaluation. MAIN OUTCOME MEASURE: Changes in diagnostic certainty of clinicians following incremental presentation of new laboratory data and the accuracy of such diagnoses. RESULTS: Clinicians used magnetic resonance imaging findings to diagnose definite MS or to eliminate MS from diagnostic consideration in 44% of cases. In these cases, further laboratory testing did not alter clinicians' decisions. In the remaining 56% of cases, in which magnetic resonance imaging did not lead to a diagnosis of definite MS or eliminate MS from diagnostic consideration, further laboratory testing led to such diagnoses in an additional 13% of cases. Gold standard diagnoses were in agreement with the clinician's assessments. CONCLUSIONS: Magnetic resonance imaging aids in the evaluation of patients suspected to have MS; other subsequent studies (computed tomography, cerebrospinal fluid analysis, and evoked potential testing) have less impact. After all studies are performed, about half of such patients still have a tentative diagnosis.

Adult↗
PubMed2002

Diffuse signal abnormalities in the spinal cord in multiple sclerosis: direct postmortem in situ magnetic resonance imaging correlated with in vitro high-resolution magnetic resonance imaging and histopathology.

In this study, we compared direct postmortem in situ (whole-corpse) sagittal spinal cord magnetic resonance imaging (1.5T) of 7 multiple sclerosis cases with targeted high-resolution in vitro axial magnetic resonance imaging (4.7T) and histopathology. On sagittal in situ magnetic resonance imaging, 1 case had a normal spinal cord, 2 had only focal lesions, 3 had a combination of focal and diffuse abnormalities, and 1 had only diffuse abnormalities. All spinal cords showed abnormalities on high-resolution magnetic resonance imaging and histopathology, confirming the existence of diffuse cord changes as genuine multiple sclerosis-related abnormalities while highlighting the limited resolution of in vivo magnetic resonance imaging.

Aged↗
PubMed1997

Dispersion in magnetization transfer contrast at a given specific absorption rate due to variations of RF pulse parameters in the magnetization transfer preparation.

The effects of RF pulse parameters on magnetization transfer contrast (MTC) were investigated using a magnetization prepared segmented fast gradient echo sequence. MTC was found not to be uniquely determined by the specific absorption rate (SAR). RF pulse parameters (RF amplitude, number of RF pulses and RF duration) also affect MTC. There can be 40% variation in MTC due to differences in RF parameters at SAR = 1 W/kg for a 70-kg subject. Increasing the number of RF pulses is a more efficient way to increase MTC than increasing RF amplitude. This phenomenon is likely caused by the fact that the time scale for magnetization transfer between the free and restricted proton pools is on the same order or longer than the duration of the MT pulse. Accordingly, increase in the MT pulse duration by increasing the number of RF pulses in the MT pulse allows more effective magnetization transfer. Such information can be used as a guide to select RF pulse parameters for a magnetization transfer (MT) pulse. An off-resonance MT pulse designed under this guide for coronary MR angiography improved the depiction of distal vessels.

Animals↗
PubMed2005

Quantification of magnetization transfer rate and native T1 relaxation time of the brain: correlation with magnetization transfer ratio measurements in patients with multiple sclerosis.

The purpose of this paper is to perform quantitative measurements of the magnetization transfer rate (Kfor) and native T1 relaxation time (T1free) in the brain tissue of normal individuals and patients with multiple sclerosis (MS) by means of multiple gradient echo acquisitions, and to correlate these measurements with the magnetization transfer ratio (MTR). Quantitative magnetization transfer imaging was performed in five normal volunteers and 12 patients with relapsing-remitting MS on a 1.5 T magnetic resonance (MR) scanner. The T1 relaxation time under magnetization transfer irradiation (T1sat) was calculated by means of fitting the signal intensity over the flip angle in several 3D spoiled gradient echo acquisitions (3 degrees , 15 degrees , 30 degrees , and 60 degrees ), while a single acquisition without MT irradiation (flip angle of 3 degrees ) was utilized to calculate the MTR. The Kfor and T1free constants were quantified on a pixel-by-pixel basis and parametric maps were reconstructed. We performed 226 measurements of Kfor, T1free, and the MTR on normal white matter (NWM) of healthy volunteers (n=50), and normal-appearing white matter (NAWM) and pathological brain areas of MS patients (n=120 and 56, respectively). Correlation coefficients between Kfor-MTR, T1free-MTR, and T1free-Kfor were calculated. Lesions were classified, according to their characteristics on T1-weighted images, into isointense (compared to white matter), mildly hypointense (showing signal intensity lower than white matter and higher than gray matter), and severely hypointense (revealing signal intensity lower than gray matter). "Dirty" white matter (DWM) corresponded to areas with diffused high signal, as identified on T2-weighted images. Strong correlation coefficients were obtained between MTR and Kfor for all lesions studied (r2=0.9, p<0.0001), for mildly hypointense plaques (r2=0.82, p<0.0001), and for DWM (r2=0.78, p=0.0007). In contrast, comparison between MTR and T1free values yielded rather low correlation coefficients for all groups assessed. In severely hypointense lesions, an excellent correlation was found between Kfor and T1free measurements (r2=0.98, p<0.0001). Strong correlations between Kfor and T1free were found for the rest of the subgroups, except for the NAWM, in which a moderate correlation was obtained (r2=0.5, p<0.0001). We conclude that Kfor and T1free measurements are feasible and may improve our understanding of the pathological brain changes that occur in MS patients.

Adult↗
PubMed1982

Magnetic fields associated with a nuclear magnetic resonance medical imaging system.

Measurements were made of magnetic and electric field levels in and around a nuclear magnetic resonance imaging system undergoing a clinical trial. Magnetic field levels ranged from 0.04 tesla (T) in the imaging volume down to about 0.0006 T at the end of the patient table. The peak radio-frequency magnetic field level was 15 amperes per meter (A/m) in the imaging volume, while the rms value was 4.6 A/m. The specific absorption rate resulting from the radio-frequency magnetic field was calculated to be no more than 0.017 watts per kilogram (W/kg). The radio-frequency electric field was detectable only within a few centimeters of the coil assembly, and does not significantly contribute to the specific absorption rate. These exposure levels were much lower than existing guidelines for clinical NMR procedures.

Clinical Trials as Topic↗
PubMedDate not supplied

Computer-assisted design of surface coils used in magnetic resonance imaging. I. The calculation of the magnetic field.

For a number of reasons, it is desirable to fabricate coils which, for a known current, shall produce predetermined values of the magnetic field intensity at a number of points within a nuclear magnetic resonance imager. The calculation of the magnetic field intensity at a set of points involves the integration of the Biot-Savart equation for all components of the segments of conductor which make up the coil. This process in itself is a rather formidable task. When this process is parameterized in terms of coil diameter, coil spacing, etc. the problem is to determine the values of these parameters to match values of magnetic field intensities which are desired. The problem thereby increases in complexity to the point where, by ordinary methods, the problem becomes intractable. This note describes an algorithm and offers a computer subroutine to calculate magnetic fields for coils of arbitrary shape and complexity for fixed currents.

Electromagnetic Fields↗
PubMed2004

A preliminary study on DNA detection based on relative magnetic permeability measurements and histone H1 conjugated superparamagnetic nanoparticles as magnetic tracers.

Histone H1 conjugated superparamagnetic nanoparticles were assessed for their ability to work as magnetic tracers in conjunction with the relative magnetic permeability metre (MPM-100) for the detection and quantification of DNA (deoxyribonucleic acid). The method employed was based on the electrostatic adsorption of DNA (analyte) to amino group derivatised silica (carrier) and subsequent binding of histone H1 conjugated superparamagnetic nanoparticles (magnetic tracer). The sandwich complexes formed were separated from the medium by sedimentation and the relative magnetic permeability of the sediments were measured with the MPM-100. Investigations were made with both calf thymus DNA and plasmid DNA in aqueous buffered solution as well as in a lysed cell culture with high protein content. For the quantification of calf thymus DNA, a linear relationship between the DNA concentration in the sample and the relative magnetic permeability of the pellet was found for DNA concentrations up to 67 microg/ml in buffered solutions as well as in a lysed cell culture. The limits of detection were determined to 12 and 31 microg/ml, respectively. For the quantification of plasmid DNA in buffered solution a linear range was established for concentrations in up to 150 microg/ml and the limit of detection was determined to 52 microg/ml.

Animals↗
PubMed1987

Combined study of 1H-magnetic resonance imaging and depth-selected, EKG-gated 31P-magnetic resonance spectroscopy of the heart in vivo.

NMR is useful for both 1H-magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS). We undertook to combine these two merits of NMR for in vivo characterization of living rat heart in wide bore (9 cm) superconducting magnet under high magnetic field (6.4 Tesla). Spatial resolution of 1H-MRI attained 0.1 mm by spin warp method. Then, depth-selected, EKG-gated 31P-MRS was performed, adjusting the detection area to cover the heart that was identified by the preceding 1H-MRI. Three evidences that 31P-SMR signal chiefly originated from the heart without cross talk of adjacent organs indicated that combination of 1H-MRI and in vivo 31P-MRS under high magnetic field in whole animal is promising for more accurate evaluation of cardiac muscle metabolism.

Animals↗
PubMed2002

Magnetic resonance cystometry: accurate assessment of bladder volume with magnetic resonance imaging.

OBJECTIVES: To evaluate magnetic resonance hydrometry for the calculation of bladder volume. The reference standard to assess bladder volume is urethral catheterization, which may be linked with the risk of trauma and infection. Hence, ultrasonography is the preferred diagnostic method. However, ultrasonography is investigator dependent and inaccurate in the hands of an inexperienced operator. METHODS: Investigations were performed in a 1.0-Tesla clinical scanner with a manufacturer-provided single-shot turbo spin-echo sequence. We examined 30 healthy volunteers (21 males and 9 females) with a mean age of 26.4 years. To quantify the volume of fluid in a magnetic resonance image, a histogram algorithm was used and a calibration phantom applied. Prevoid and postvoid images were acquired. The bladder volume was calculated as the difference between the prevoid and postvoid image fluid volumes. The magnetic resonance-calculated data were compared with the actually voided volumes. RESULTS: The measured voided bladder volume was 400 +/- 33 mL, whereas magnetic resonance hydrometry yielded 390 +/- 31 mL. The difference between both measurements was not statistically significant. The 95% confidence interval for the difference of both measurements ranged from -22.6 to 2.4 mL. The regression had an r2 of 0.97. CONCLUSIONS: The feasibility of magnetic resonance hydrometry to quantify the bladder volume noninvasively was demonstrated.

Adult↗
PubMed2005

In vivo magnetic resonance detection of cancer by using multifunctional magnetic nanocrystals.

The unique properties of magnetic nanocrystals provide them with high potential as key probes and vectors in the next generation of biomedical applications. Although superparamagnetic iron oxide nanocrystals have been extensively studied as excellent magnetic resonance imaging (MRI) probes for various cell trafficking, gene expression, and cancer diagnosis, further development of in vivo MRI applications has been very limited. Here, we describe in vivo diagnosis of cancer, utilizing a well-defined magnetic nanocrystal probe system with multiple capabilities, such as small size, strong magnetism, high biocompatibility, and the possession of active functionality for desired receptors. Our magnetic nanocrystals are conjugated to a cancer-targeting antibody, Herceptin, and subsequent utilization of these conjugates as MRI probes has been successfully demonstrated for the monitoring of in vivo selective targeting events of human cancer cells implanted in live mice. Further conjugation of these nanocrystal probes with fluorescent dye-labeled antibodies enables both in vitro and ex vivo optical detection of cancer as well as in vivo MRI, which are potentially applicable for an advanced multimodal detection system. Our study finds that high performance in vivo MR diagnosis of cancer is achievable by utilizing improved and multifunctional material properties of iron oxide nanocrystal probes.

Animals↗
PubMed2005

Bio-functionalization of monodisperse magnetic nanoparticles and their use as biomolecular labels in a magnetic tunnel junction based sensor.

Monodisperse magnetic nanoparticles (NPs) could enable the ultra-sensitive magnetic detection of biological analytes. However, rendering these particles biocompatible has remained a challenge. We report the bio-functionalization and detection of 12-nm manganese ferrite NPs. We have achieved the site-specific binding of biotin-functionalized NPs onto avidin-patterned silicon oxide substrates and DNA-functionalized NPs onto complementary DNA-patterned silicon oxide substrates. Utilizing scanning SQUID microscopy, we show that these substrate-bound NPs retain their magnetic properties. Finally, we demonstrate a novel method of detecting either protein binding or DNA hybridization at room temperature using the NPs and a magnetic tunnel-junction-based biosensor situated in orthogonal magnetic fields.

Avidin↗
PubMed2006

The spin mixing process of a radical pair in low magnetic field observed by transient absorption detected nanosecond pulsed magnetic field effect.

The spin mixing process of the radical pair in the sodium dodecyl sulfate (SDS) micelle is studied by using a novel technique nanosecond pulsed magnetic field effect on transient absorption. We have developed the equipment for a nanosecond pulsed magnetic field and observed its effect on the radical pair reaction. A decrease of the free radical yield by a reversely directed pulsed magnetic field that cancels static field is observed, and the dependence on its magnitude, which is called pulsed MARY (magnetic field effect on reaction yield) spectra, is studied. The observed spectra reflect the spin mixing in 50-200 ns and show clear time evolution. Theoretical simulation of pulsed MARY spectra based on a single site modified Liouville equation indicates that the fast spin dephasing processes induced by the modulation of electron-electron spin interaction by molecular reencounter affect to the coherent spin mixing by a hyperfine interaction in a low magnetic field.

Free Radicals↗
PubMed2005

Magnetic targeting and cellular uptake of polymer microcapsules simultaneously functionalized with magnetic and luminescent nanocrystals.

By using a flow channel system for modeling the bloodstream in the circulatory system and by locally creating a magnetic field gradient caused by a permanent magnet, we demonstrate specific trapping of polymer capsules simultaneously functionalized with two types of nanoparticles--magnetic and luminescent nanocrystals. In the regions where the capsules were trapped by the magnetic field, drastically increased uptake of capsules by cells has been observed. The uptake of capsules by cells could be conveniently monitored with a fluorescence microscope by the luminescence of CdTe nanocrystals that had been embedded into the shells of the capsules. Our experiments envisage the feasibility of magnetic targeting of polymer capsules loaded by pharmaceutical agents to pathogenic parts of a tissue.

Breast Neoplasms↗
PubMed2003

A nanoporous molecular magnet with reversible solvent-induced mechanical and magnetic properties.

Interest in metal-organic open-framework structures has increased enormously in the past few years because of the potential benefits of using crystal engineering techniques to yield nanoporous materials with predictable structures and interesting properties. Here we report a new efficient methodology for the preparation of metal-organic open-framework magnetic structures based on the use of a persistent organic free radical (PTMTC), functionalized with three carboxylic groups. Using this approach, we create an open-framework structure Cu3(PTMTC)2(py)6(CH3CH2OH)2(H2O), which we call MOROF-1, combining very large pores (2.8-3.1 nm) with bulk magnetic ordering. MOROF-1 shows a reversible and highly selective solvent-induced 'shrinking-breathing' process involving large volume changes (25-35%) that strongly influence the magnetic properties of the material. This magnetic sponge-like behaviour could be the first stage of a new route towards magnetic solvent sensors.

Copper↗
PubMed1971

Magnetic anisotropy and the orientation of retinal rods in a homogeneous magnetic field.

The reported orientation of retinal rods in a homogeneous magnetic field can be explained by the magnetic anisotropy of oriented molecules in the disc membranes of the rods. The energy of a single rod as a function of orientation in the magnetic field, the time required for alingment of the rod in a viscous medium, and the fluctuations of orientation are calculated. Arguments that rhodopsin is the constituent responsible for the effect are given. The possibility of orientation due to inhomogeneity of the magnetic field is ruled out. The application of magnetic anisotropy as an experimental tool in biology is indicated.

Animals↗
PubMed2006

Health risk assessment of occupational exposure to a magnetic field from magnetic resonance imaging devices.

Health care staff who operate magnetic resonance imaging (MRI) devices are exposed to a static magnetic field of significant spatial heterogenity always produced by MRI magnets during the whole shift. They can also be exposed to pulses of a time-varying magnetic field (gradient field) present only during patients' examinations. The level of the workers' exposure depends both on the type of the magnet and on the ergonomic design of each MRI device. The paper presents methods used for measuring and assessing workers' exposure. It also discusses the results of inspection measurements carried out next to approximately 20 MRI devices of approximately 0.2-2.0 T. The presented characteristic and overview of the variability of workers' exposure to a variety of MRI devices supports the need for data on monitoring occupational exposure to MRI. International exposure assessment standards and guidelines (International Commission on Non-Ionizing Radiation Protection [ICNIRP], Institute of Electrical and Electronics Engineers [IEEE], American Conference of Governmental and Industrial Hygienists [ACGIH], European Commission directive), and those established in Poland are also compared.

Electromagnetic Fields↗