Mechanisms for Biological Effects of Magnetic Fields

Tenforde, T.S.

doi:10.1007/978-1-4613-2099-9_5

Cited by 23 publications

(17 citation statements)

References 54 publications

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“…The main concern about the interaction between the electrode and the time‐varying magnetic field is the presence of a conducting loop. An electromotive force may be induced by the gradient coil and RF pulses in the conduction loop formed by the microelectrode, reference electrode, and brain tissues inside the bore, and this current, which is comparable to the externally applied current, can occur during both the ON and OFF periods, making the results difficult to interpret (25). In our experimental setup, we minimized the induced current by decreasing the area of the conducting loop, and made the conducting loop approximately parallel to the B 1 field so that it would induce a lower voltage within the RF field.…”

Section: Discussionmentioning

confidence: 99%

BOLD response to direct thalamic stimulation reveals a functional connection between the medial thalamus and the anterior cingulate cortex in the rat

Shyu

Lin

Sun

et al. 2004

Magnetic Resonance in Med

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Recent functional neuroimaging studies in humans and rodents have shown that the anterior cingulate cortex (ACC) is activated by painful stimuli, and plays an important role in the affective aspect of pain sensation. The aim of the present study was to develop a suitable stimulation method for direct activation of the brain in fMRI studies and to investigate the functional connectivity in the thalamo-cingulate pathway. In the first part of the study, tungsten, stainless steel, or glass-coated carbon fiber microelectrodes were implanted in the left medial thalamus (MT) of anesthetized rats, and T 2 *-weighted gradient-echo (GE) images were obtained in the sagittal plane on a 4.7 T system (Biospec BMT 47/40). Only the images obtained with the carbon fiber electrode were acceptable without a reduction of the signal-to-noise ratio (SNR) and image distortion. In the second part of the study, a series of two-slice GE images were acquired during electrical stimulation of the MT with the use of a carbon fiber electrode. A cross-correlation analysis showed that the signal intensities of activated areas in the ipsilateral Functional MRI (fMRI) is a noninvasive imaging technique for mapping brain function that utilizes neuronal activityinduced changes in blood oxygenation. These changes result in a high local concentration of deoxyhemoglobin, the paramagnetic properties of which cause blood oxygen level-dependent (BOLD) contrast (1,2). fMRI provides spatial information about multiple brain activations, and allows the functional assessment of specific sensory pathways; therefore, it is increasingly being used to elucidate the functional organization of the human brain (3). However, current fMRI methods are of limited use in exploring longrange interactions between different brain structures and specific functional activation by known neuroanatomical pathways, which require the invasive implantation of an intracranial stimulation electrode or cannula to electrically or chemically excite specific brain structures.Invasive stimulation of a deep brain region has long been used in patients to alleviate intractable pain (4,5), and a recent study using PET imaging demonstrated that the anterior cingulate cortex (ACC) is activated during thalamic deep brain stimulation in patients with chronic pain (6). However, the use of direct electrical brain stimulation in fMRI studies has potential hazards associated with the direct application of electrical current to brain tissue in the magnetic bore, and thus there is a need for a safe, efficient method for electrical brain stimulation in such studies. Several MR-compatible electrical stimulation methods for use in humans have been developed (7-10), but the strong magnetic field interference elicited by metal electrodes is still a problem in direct electrical brain stimulation in fMRI studies.fMRI studies using animal models allow invasive investigation of the neuronal mechanism underlying the brain activation shown by the BOLD signals (11). Furthermore, studies of the effect of pharmacolo...

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Section: Discussionmentioning

confidence: 99%

BOLD response to direct thalamic stimulation reveals a functional connection between the medial thalamus and the anterior cingulate cortex in the rat

Shyu

Lin

Sun

et al. 2004

Magnetic Resonance in Med

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“…Static magnetic fields exert electrodynamic forces on moving ions in blood vessels, generating an electric potential across the blood vessels (Hall effect) and theoretically a reduction of blood flow velocity (Tenforde 1992)-a 5 and 10% reduction in blood flow in the aorta was predicted to occur in static fields of 10 and 15 T, respectively, due to magneto-hydrodynamic interactions (Kinouchi et al 1996). Related observations included a change in blood velocity of an order of a 0.2%-3% in the case of exposure to static fields of the level increasing from 1 T to 10 T (Dorfman 1971;Keltner 1990).…”

Section: Biological and Health Consequences Of Electromagnetic Fieldsmentioning

confidence: 99%

Occupational risk from static magnetic fields of MRI scanners

2007

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The health care staff operating magnetic resonance imaging (MRI) scanners are exposed to static magnetic field of significant spatial heterogenity and high level of flux density-usually existing permanently during the shift. The personnel can also be exposed to pulses of magnetic field of high rate of rise/fall, so-called gradient fields, which exist only during examination of patients. The level of workers' exposure depends both on the type of the magnet and on the ergonomical characteristic of design of the particular MRI scanner. This paper presents the current state of the art on occupational exposure to static magnetic field health effects, gaps in scientific data, MRI workers' exposure characteristics, research needs, and suggestions for the exposure assessment protocol for future investigations.

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“…During the decade from 1976 to 1986, my colleagues at LBNL, along with numerous collaborators, studied the possible effects of exposure to large static magnetic fields on the functions of many major organ and tissue systems. In addition to the studies on the cardiovascular system described above, it was found that exposure to fields with flux densities up to 2 T have no measurable effects on nerve bioelectric activity [Gaffey and Tenforde, 1983], animal behavior [Davis et al, 1984], vision [Tenforde, 1992], immune system competence [Tenforde and Shifrine, 1984], thermoregulatory capacity [Tenforde, 1986b], and physiological regulation and circadian rhythms [Tenforde, 1984;Tenforde et al, 1987]. As in the cardiovascular studies on animals exposed to strong magnetic fields, many of the experiments on animal physiology and behavior required the design and fabrication of customized, nonmagnetic transducers and other specialized equipment.…”

Section: Magnetic Field Dosimetry and Bioeffectsmentioning

confidence: 99%

“…These studies included an analysis of electrodynamic interactions with blood and nervous tissues, magnetomechanical orientation effects on magnetically anisotropic structures (e.g., DNA macromolecules, liposomal phospholipid bilayer membranes, and retinal rod disk membranes), and magnetic field effects on physiological regulation and animal behavior. The results of many of these studies were summarized in a review by the author [Tenforde, 1992]. Of these many studies, I will describe in detail only the extensive experimental and theoretical studies that were conducted on the electrodynamic and magnetohydrodynamic interactions of static magnetic fields with the cardiovascular system.…”

Section: Magnetic Field Dosimetry and Bioeffectsmentioning

confidence: 99%

The wonders of magnetism

Tenforde

2002

Bioelectromagnetics

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In this acceptance address for the Bioelectromagnetics Society's 2001 d'Arsonval Award, Dr. Tenforde reviews the highlights of the nonionizing field aspects of his research and scientific service career. These are focused in four areas: (a). development and application of microelectrophoretic methods to probe the surface chemistry of normal and cancerous cells; (b). research on the biophysical mechanisms of interaction and the dosimetry of static and extremely low frequency magnetic fields; (c). application of extremely high intensity magnetic fields in several spectroscopic methods for probing the detailed structures of large biological macromolecules; and (d). development of national and international guidelines for the exposure of workers and members of the general public to electromagnetic fields with frequencies spanning the entire nonionizing electromagnetic spectrum.

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Mechanisms for Biological Effects of Magnetic Fields

Cited by 23 publications

References 54 publications

BOLD response to direct thalamic stimulation reveals a functional connection between the medial thalamus and the anterior cingulate cortex in the rat

BOLD response to direct thalamic stimulation reveals a functional connection between the medial thalamus and the anterior cingulate cortex in the rat

Occupational risk from static magnetic fields of MRI scanners

The wonders of magnetism

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