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RF Fields (rf + field)
Selected AbstractsEffects of RF inhomogeneity at 3.0T on ramped RF excitation: Application to 3D time-of-flight MR angiography of the intracranial arteries,JOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 3 2007Amir M. Eissa MSc Abstract Purpose To demonstrate the effects of inherent RF inhomogeneity on ramped RF excitation at 3.0T, and to introduce a simple correction for improving visualization of distal intracranial arteries in three-dimensional time-of-flight MR angiography (3D-TOF-MRA). Materials and Methods At 3.0T, the effects of RF inhomogeneity arising from RF interference were demonstrated for ramped RF excitation in intracranial 3D-TOF-MRA. Computer simulations and experiments on phantoms and eight normal volunteers were performed. Four different ramp shapes were tested as a possible means of countering the reduced RF field that affects the distal intracranial arteries. Results RF destructive interference alters the ramp pulse shape, which is problematic for vessels that proceed from the center to the edge of the brain. Increasing the ramp pulse slope was shown to be an effective yet simple correction to counter the falling-off of the RF field toward the periphery of the head. With this approach, circle-of-Willis 3D-TOF-MRA studies had improved distal visibility. Conclusion Ramped RF excitation is severely affected by RF interference at 3.0T, which makes the ramp profile suboptimal for distal intracranial blood vessels. A simple correction of the ramp slope can make a marked improvement. J. Magn. Reson. Imaging 2007. © 2007 Wiley-Liss, Inc. [source] Manipulation of image intensity distribution at 7.0 T: Passive RF shimming and focusing with dielectric materials,JOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 1 2006Qing X. Yang Abstract Purpose To investigate the effects of high dielectric material padding on RF field distribution in the human head at 7.0 T, and demonstrate the feasibility and effectiveness of RF passive shimming and focusing with such an approach. Materials and Methods The intensity distribution changes of gradient-recalled-echo (GRE) and spin-echo (SE) images of a human head acquired with water pads (dielectric constant = 78) placed in specified configurations around the head at 7.0 T were evaluated and compared with computer simulation results using the finite difference time domain (FDTD) method. The contributions to the B1 field distribution change from the displacement current and conductive current of a given configuration of dielectric padding were determined with computer simulations. Results MR image intensity distribution in the human head with an RF coil at 7.0 T can be changed drastically by placing water pads around the head. Computer simulations reveal that the high permittivity of water pads results in a strong displacement current that enhances image intensity in the nearby region and alters the intensity distribution of the entire brain. Conclusion The image intensity distribution in the human head at ultra-high field strengths can be effectively manipulated with high permittivity padding. Utilizing this effect, the B1 field inside the human head of a given RF coil can be adjusted to reduce the B1 field inhomogeneity artifact associated with the wave behavior (RF passive shimming) or to locally enhance the signal-to-noise ratio (SNR) in targeted regions of interest (ROIs; RF field focusing). J. Magn. Reson. Imaging 2006. © 2006 Wiley-Liss, Inc. [source] Radiofrequency exposure on fast patrol boats in the Royal Norwegian Navy,an approach to a dose assessmentBIOELECTROMAGNETICS, Issue 5 2010Valborg Baste Abstract Epidemiological studies related to radiofrequency (RF) electromagnetic fields (EMF) have mainly used crude proxies for exposure, such as job titles, distance to, or use of different equipment emitting RF EMF. The Royal Norwegian Navy (RNoN) has measured RF field emitted from high-frequency antennas and radars on several spots where the crew would most likely be located aboard fast patrol boats (FPB). These boats are small, with short distance between the crew and the equipment emitting RF field. We have described the measured RF exposure aboard FPB and suggested different methods for calculations of total exposure and annual dose. Linear and spatial average in addition to percentage of ICNIRP and squared deviation of ICNIRP has been used. The methods will form the basis of a job exposure matrix where relative differences in exposure between groups of crew members can be used in further epidemiological studies of reproductive health. Bioelectromagnetics 31:350,360, 2010. © 2010 Wiley-Liss, Inc. [source] 1950,MHz IMT-2000 field does not activate microglial cells in vitroBIOELECTROMAGNETICS, Issue 2 2010Hideki Hirose Abstract Given the widespread use of the cellular phone today, investigation of potential biological effects of radiofrequency (RF) fields has become increasingly important. In particular, much research has been conducted on RF effects on brain function. To examine any biological effects on the central nervous system (CNS) induced by 1950,MHz modulation signals, which are controlled by the International Mobile Telecommunication-2000 (IMT-2000) cellular system, we investigated the effect of RF fields on microglial cells in the brain. We assessed functional changes in microglial cells by examining changes in immune reaction-related molecule expression and cytokine production after exposure to a 1950,MHz Wideband Code Division Multiple Access (W-CDMA) RF field, at specific absorption rates (SARs) of 0.2, 0.8, and 2.0,W/kg. Primary microglial cell cultures prepared from neonatal rats were subjected to an RF or sham field for 2,h. Assay samples obtained 24 and 72,h after exposure were processed in a blind manner. Results showed that the percentage of cells positive for major histocompatibility complex (MHC) class II, which is the most common marker for activated microglial cells, was similar between cells exposed to W-CDMA radiation and sham-exposed controls. No statistically significant differences were observed between any of the RF field exposure groups and the sham-exposed controls in percentage of MHC class II positive cells. Further, no remarkable differences in the production of tumor necrosis factor-, (TNF-,), interleukin-1, (IL-1,), and interleukin-6 (IL-6) were observed between the test groups exposed to W-CDMA signal and the sham-exposed negative controls. These findings suggest that exposure to RF fields up to 2,W/kg does not activate microglial cells in vitro. Bioelectromagnetics 31:104,112, 2010. © 2009 Wiley-Liss, Inc. [source] Mobile phone base station-emitted radiation does not induce phosphorylation of Hsp27BIOELECTROMAGNETICS, Issue 2 2007H. Hirose Abstract An in vitro study focusing on the effects of low-level radiofrequency (RF) fields from mobile radio base stations employing the International Mobile Telecommunication 2000 (IMT-2000) cellular system was conducted to test the hypothesis that modulated RF fields act to induce phosphorylation and overexpression of heat shock protein hsp27. First, we evaluated the responses of human cells to microwave exposure at a specific absorption rate (SAR) of 80 mW/kg, which corresponds to the limit of the average whole-body SAR for general public exposure defined as a basic restriction in the International Commission on Non-Ionizing Radiation Protection (ICNIRP) guidelines. Second, we investigated whether continuous wave (CW) and Wideband Code Division Multiple Access (W-CDMA) modulated signal RF fields at 2.1425 GHz induced activation or gene expression of hsp27 and other heat shock proteins (hsps). Human glioblastoma A172 cells were exposed to W-CDMA radiation at SARs of 80 and 800 mW/kg for 2,48 h, and CW radiation at 80 mW/kg for 24 h. Human IMR-90 fibroblasts from fetal lungs were exposed to W-CDMA at 80 and 800 mW/kg for 2 or 28 h, and CW at 80 mW/kg for 28 h. Under the RF field exposure conditions described above, no significant differences in the expression levels of phosphorylated hsp27 at serine 82 (hsp27[pS82]) were observed between the test groups exposed to W-CDMA or CW signal and the sham-exposed negative controls, as evaluated immediately after the exposure periods by bead-based multiplex assays. Moreover, no noticeable differences in the gene expression of hsps were observed between the test groups and the negative controls by DNA Chip analysis. Our results confirm that exposure to low-level RF field up to 800 mW/kg does not induce phosphorylation of hsp27 or expression of hsp gene family. Bioelectromagnetics © 2006 Wiley-Liss, Inc. [source] Effects of exposure to a 1950 MHz radio frequency field on expression of Hsp70 and Hsp27 in human glioma cellsBIOELECTROMAGNETICS, Issue 4 2005J. Miyakoshi Abstract Human glioma MO54 cells were used to investigate whether radio frequency (RF) field exposure could activate stress response genes. Cells were exposed to continuous wave 1950 MHz or sham conditions for up to 2 h. Specific absorption rates (SARs) were 1, 2, and 10 W/kg. For the cell growth experiment, cell numbers were counted at 0,4 days after exposure. Expression of Hsp27 and Hsp70, as well as the level of phosphorylated Hsp27 (78Ser) protein, was determined by Western blotting. It was found that sham exposed and RF exposed cells demonstrated a similar growth pattern up to 4 days after RF field exposure. RF field exposure at both 2 and 10 W/kg did not affect the growth of MO54 cells. In addition, there were no significant differences in protein expression of Hsp27 and Hsp70 between sham exposed and RF exposed cells at a SAR of 1, 2, or 10 W/kg for 1 and 2 h. However, exposure to RF field at a SAR of 10 W/kg for 1 and 2 h decreased the protein level of phosphorylated Hsp27 (78Ser) significantly. Our results suggest that although exposure to a 1950 MHz RF field has no effect on cell proliferation and expression of Hsp 27 and Hsp70, it may inhibit the phosphorylation of Hsp27 at Serine 78 in MO54 cells. Bioelectromagnetics 26:251,257, 2005. © 2005 Wiley-Liss, Inc. [source] NMR and the uncertainty principle: How to and how not to interpret homogeneous line broadening and pulse nonselectivity.CONCEPTS IN MAGNETIC RESONANCE, Issue 5 2008IV. (Un?)certainty Abstract Following the treatments presented in Parts I, II, and III, I herein address the popular notion that the frequency of a monochromatic RF pulse as well as that of a monochromatic FID is "in effect" uncertain due to the (Heisenberg) Uncertainty Principle, which also manifests itself in the fact that the FT-spectrum of these temporal entities is spread over a nonzero frequency band. I will show that the frequency spread should not be interpreted as "in effect" meaning a range of physical driving RF fields in the former, and "spin frequencies" in the latter case. The fact that a shorter pulse or a more quickly decaying FID has a wider FT-spectrum is in fact solely due to the Fourier Uncertainty Principle, which is a less well known and easily misunderstood concept. A proper understanding of the Fourier Uncertainty Principle tells us that the FT-spectrum of a monochromatic pulse is not "broad" because of any "uncertainty" in the RF frequency, but because the spectrum profile carries all of the pulse's features (frequency, phase, amplitude, length, temporal location) coded into the complex amplitudes of the FT-spectrum's constituent eternal basis harmonic waves. A monochromatic RF pulse's capability to excite nonresonant magnetizations is in fact a purely classical off-resonance effect that has nothing to do with "uncertainty". Analogously, "Lorentzian lineshape" means exactly the same thing physically as "exponential decay," and all inferences as to the physical reasons for that decay must be based on independent assumptions or observations. © 2008 Wiley Periodicals, Inc. Concepts Magn Reson Part A 32A: 373,404, 2008. [source] 1950,MHz IMT-2000 field does not activate microglial cells in vitroBIOELECTROMAGNETICS, Issue 2 2010Hideki Hirose Abstract Given the widespread use of the cellular phone today, investigation of potential biological effects of radiofrequency (RF) fields has become increasingly important. In particular, much research has been conducted on RF effects on brain function. To examine any biological effects on the central nervous system (CNS) induced by 1950,MHz modulation signals, which are controlled by the International Mobile Telecommunication-2000 (IMT-2000) cellular system, we investigated the effect of RF fields on microglial cells in the brain. We assessed functional changes in microglial cells by examining changes in immune reaction-related molecule expression and cytokine production after exposure to a 1950,MHz Wideband Code Division Multiple Access (W-CDMA) RF field, at specific absorption rates (SARs) of 0.2, 0.8, and 2.0,W/kg. Primary microglial cell cultures prepared from neonatal rats were subjected to an RF or sham field for 2,h. Assay samples obtained 24 and 72,h after exposure were processed in a blind manner. Results showed that the percentage of cells positive for major histocompatibility complex (MHC) class II, which is the most common marker for activated microglial cells, was similar between cells exposed to W-CDMA radiation and sham-exposed controls. No statistically significant differences were observed between any of the RF field exposure groups and the sham-exposed controls in percentage of MHC class II positive cells. Further, no remarkable differences in the production of tumor necrosis factor-, (TNF-,), interleukin-1, (IL-1,), and interleukin-6 (IL-6) were observed between the test groups exposed to W-CDMA signal and the sham-exposed negative controls. These findings suggest that exposure to RF fields up to 2,W/kg does not activate microglial cells in vitro. Bioelectromagnetics 31:104,112, 2010. © 2009 Wiley-Liss, Inc. [source] Continuous wave and simulated GSM exposure at 1.8 W/kg and 1.8 GHz do not induce hsp16-1 heat-shock gene expression in Caenorhabditis elegansBIOELECTROMAGNETICS, Issue 2 2008Adam S. Dawe Abstract Recent data suggest that there might be a subtle thermal explanation for the apparent induction by radiofrequency (RF) radiation of transgene expression from a small heat-shock protein (hsp16-1) promoter in the nematode, Caenorhabditis elegans. The RF fields used in the C. elegans study were much weaker (SAR 5,40 mW,kg,1) than those routinely tested in many other published studies (SAR ,2 W,kg,1). To resolve this disparity, we have exposed the same transgenic hsp16-1::lacZ strain of C. elegans (PC72) to higher intensity RF fields (1.8 GHz; SAR ,1.8 W,kg,1). For both continuous wave (CW) and Talk-pulsed RF exposures (2.5 h at 25 °C), there was no indication that RF exposure could induce reporter expression above sham control levels. Thus, at much higher induced RF field strength (close to the maximum permitted exposure from a mobile telephone handset), this particular nematode heat-shock gene is not up-regulated. However, under conditions where background reporter expression was moderately elevated in the sham controls (perhaps as a result of some unknown co-stressor), we found some evidence that reporter expression may be reduced by ,15% following exposure to either Talk-pulsed or CW RF fields. Bioelectromagnetics 29:92,99, 2008. © 2007 Wiley-Liss, Inc. [source] Mobile phone base station-emitted radiation does not induce phosphorylation of Hsp27BIOELECTROMAGNETICS, Issue 2 2007H. Hirose Abstract An in vitro study focusing on the effects of low-level radiofrequency (RF) fields from mobile radio base stations employing the International Mobile Telecommunication 2000 (IMT-2000) cellular system was conducted to test the hypothesis that modulated RF fields act to induce phosphorylation and overexpression of heat shock protein hsp27. First, we evaluated the responses of human cells to microwave exposure at a specific absorption rate (SAR) of 80 mW/kg, which corresponds to the limit of the average whole-body SAR for general public exposure defined as a basic restriction in the International Commission on Non-Ionizing Radiation Protection (ICNIRP) guidelines. Second, we investigated whether continuous wave (CW) and Wideband Code Division Multiple Access (W-CDMA) modulated signal RF fields at 2.1425 GHz induced activation or gene expression of hsp27 and other heat shock proteins (hsps). Human glioblastoma A172 cells were exposed to W-CDMA radiation at SARs of 80 and 800 mW/kg for 2,48 h, and CW radiation at 80 mW/kg for 24 h. Human IMR-90 fibroblasts from fetal lungs were exposed to W-CDMA at 80 and 800 mW/kg for 2 or 28 h, and CW at 80 mW/kg for 28 h. Under the RF field exposure conditions described above, no significant differences in the expression levels of phosphorylated hsp27 at serine 82 (hsp27[pS82]) were observed between the test groups exposed to W-CDMA or CW signal and the sham-exposed negative controls, as evaluated immediately after the exposure periods by bead-based multiplex assays. Moreover, no noticeable differences in the gene expression of hsps were observed between the test groups and the negative controls by DNA Chip analysis. Our results confirm that exposure to low-level RF field up to 800 mW/kg does not induce phosphorylation of hsp27 or expression of hsp gene family. Bioelectromagnetics © 2006 Wiley-Liss, Inc. [source] Editor's note: Reviews of the effects of RF fields on various aspects of human healthBIOELECTROMAGNETICS, Issue S6 2003Ben Greenebaum Editor in Chief No abstract is available for this article. [source] Reviews of effects of RF fields on various aspects of human health: Introduction,BIOELECTROMAGNETICS, Issue S6 2003C-K. Chou No abstract is available for this article. [source] Hypersensitivity symptoms associated with exposure to cellular telephones: No causal linkBIOELECTROMAGNETICS, Issue 4 2002Maila Hietanen Abstract The hypothesis that there exist hypersensitive persons who perceive subjective symptoms from radiofrequency (RF) fields emitted by hand held mobile phones (cellular phones) was tested using double blind provocation experiments. We also tested whether sensitive subjects are able to determine whether the phone is on or off by sensing RF fields. The study group consisted of 20 volunteers (13 women and 7 men) who reported themselves as being sensitive to cellular phones. The RF exposure sources were one analogue NMT phone (900 MHz) and two digital GSM phones (900 and 1800 MHz). The duration of a test session was 30 min, and three or four sessions were performed in random order for each subject during 1 day. The subjects were asked to report symptoms or sensations as soon as they perceived any abnormal feelings. In addition, the subjects' blood pressure, heart rate, and breathing frequency were monitored every 5 min. The results of the study indicated that various symptoms were reported, and most of them appeared in the head region. However, the number of reported symptoms was higher during sham exposure than during real exposure conditions. In addition, none of the test persons could distinguish real RF exposure from sham exposure. Hence, we conclude that adverse subjective symptoms or sensations, though unquestionably perceived by the test subjects, were not produced by cellular phones. Bioelectromagnetics 23:264,270, 2002. © 2002 Wiley-Liss, Inc. [source] Partial-body exposure of human volunteers to 2450,MHz pulsed or CW fields provokes similar thermoregulatory responses,BIOELECTROMAGNETICS, Issue 4 2001Eleanor R. Adair Abstract Many reports describe data showing that continuous wave (CW) and pulsed (PW) radiofrequency (RF) fields, at the same frequency and average power density (PD), yield similar response changes in the exposed organism. During whole-body exposure of squirrel monkeys at 2450 MHz CW and PW fields, heat production and heat loss responses were nearly identical. To explore this question in humans, we exposed two different groups of volunteers to 2450,MHz CW (two females, five males) and PW (65,,s pulse width, 104,pps; three females, three males) RF fields. We measured thermophysiological responses of heat production and heat loss (esophageal and six skin temperatures, metabolic heat production, local skin blood flow, and local sweat rate) under a standardized protocol (30,min baseline, 45,min RF or sham exposure, 10,min baseline), conducted in three ambient temperatures (Ta,=,24, 28, and 31°C). At each Ta, average PDs studied were 0, 27, and 35,mW/cm2 (Specific absorption rate (SAR),=,0, 5.94, and 7.7,W/kg). Mean data for each group showed minimal changes in core temperature and metabolic heat production for all test conditions and no reliable differences between CW and PW exposure. Local skin temperatures showed similar trends for CW and PW exposure that were PD-dependent; only the skin temperature of the upper back (facing the antenna) showed a reliably greater increase (P,=,.005) during PW exposure than during CW exposure. Local sweat rate and skin blood flow were both Ta - and PD-dependent and showed greater variability than other measures between CW and PW exposures; this variability was attributable primarily to the characteristics of the two subject groups. With one noted exception, no clear evidence for a differential response to CW and PW fields was found. Bioelectromagnetics 22:246,259, 2001. © 2001 Wiley-Liss, Inc. [source] Nocebo as headache trigger: evidence from a sham-controlled provocation study with RF fieldsACTA NEUROLOGICA SCANDINAVICA, Issue 2008L. J. Stovner Background ,, A large proportion of the population in Norway has experienced headache in connection with mobile phone use, but several double-blind provocation studies with radiofrequency (RF) and sham exposures have shown no relation between headache and mobile phone RF fields. Aims ,, To investigate the type and location of headache experienced by participants in one provocation study in order to gain insight into possible causes and mechanisms of the headaches. Method ,, Questionnaire about headache, indication on figure of location of headache after exposure, interview with neurologist about headache features to make headache diagnoses. Results ,, The 17 participants went through 130 trials (sham or RF exposure). No significant difference existed in headache type, laterality or location between the headaches experienced with the two exposures types. In most participants, the headache was compatible with tension-type headache. Discussion ,, As participants experienced their typical ,mobile phone headache' both with and without RF exposure, and since the experiment did not involve the stress or the arm/head position of mobile phone use, the most likely explanation is that the headache in this situation is caused by negative expectations (nocebo). Conclusion ,, This and other similar studies indicate that headache occurring in connection with mobile phone use is not related to RF fields, and that a nocebo effect is important for this and possibly other headache triggers. [source] | ||||||||||