bluuebunny/crossref_metadata_2025_split huggingface dataset:
Detection of DNA double‐strand breaks using γh2AX after MRI exposure at 3 Tesla: An in vitro study
Authors: Schwenzer Nina F. , Bantleon Rüdiger , Maurer Brigitte , Kehlbach Rainer , Schraml Christina , Claussen Claus D. , Rodegerdts Enno 
Published: October 2007

AbstractPurposeTo evaluate the effects of the static magnetic field and typical imaging sequences of a high‐field magnetic resonance scanner (3 Tesla) on the induction of double‐strand breaks (DSBs) in two different human cell lines.Materials and MethodsHuman promyelocytic leukemia cells (HL‐60) and human acute myeloid leukemia cells (KG‐1a) were exposed to the static magnetic field alone and to turbo spin‐echo (TSE) and gradient‐echo (GE) sequences. Flow cytometry was used to quantify γH2AX (serine 139 phosphorylated form of histone H2AX) expression of antibody‐stained cells as a marker for deoxyribonucleic acid (DNA) DSBs one hour and 24 hours after magnetic field exposure. X‐ray–treated cells were used as positive control.ResultsNeither exposure to the static magnetic field alone nor to the applied imaging sequences showed significant differences in γH2AX expression between exposed and sham‐exposed cells. X‐ray–treated cells as positive control showed a significant increase in γH2AX expression.ConclusionThe static magnetic field alone and MRI sequences at 3 Tesla have no effect on the induction of DSBs in HL‐60 and KG‐1a cells. J. Magn. Reson. Imaging 2007;26:1308–1314. © 2007 Wiley‐Liss, Inc.
Measurements of occupational exposure to switched gradient and spatially‐varying magnetic fields in areas adjacent to 1.5T clinical MRI systems
Authors: Riches Sophie F. , Collins David J. , Charles‐Edwards Geoffrey D. , Shafford Jonathan C. , Cole Jonathan , Keevil Stephen F. , Leach Martin O. 
Published: October 2007

AbstractPurposeTo determine if magnetic field exposure close to two clinical 1.5T magnetic resonance imaging (MRI) scanners during image acquisition and when moving in the spatially‐varying static magnetic field is compliant with European Union (EU) Directive 2004/40/EC (the Directive).Materials and MethodsUsing commercially available equipment we measured the magnetic flux density around the scanners during two clinical pulse sequences. The data was compared with frequency‐dependent limits that will limit occupational exposure following transposition of the Directive into national law in 2008. The static magnetic field was measured around the scanners and the exposure from movement within this field was simulated.ResultsThe whole‐body exposure experienced when standing close to the face of the magnet exceeds the limits in the Directive on the two scanners tested during clinical sequences. Simulation of movement toward the scanner shows that speeds must be restricted to 1/5 of normal walking speed to comply with the Directive.ConclusionEU Directive 2004/40/EC will have a major impact on the current use and future development of MRI due to limitations on exposure to time‐varying gradient fields and movement within the spatially‐varying static field. This will make interventional work impossible and routine MRI use impracticable in Europe. J. Magn. Reson. Imaging 2007;26:1346–1352. © 2007 Wiley‐Liss, Inc.
Standards for medical devices in MRI: Present and future
Authors: Woods Terry O. 
Published: October 2007

AbstractThe purpose of this review is to define the current standards addressing safety of medical devices in MRI and to describe ongoing standards development efforts. The American Society for Testing and Materials (ASTM International) began developing standard test methods for determining the MR safety of medical devices in MRI in 1997. To date, five ASTM standards addressing testing and marking medical devices and other items for use in the MR environment have been published. International Standards Organization (ISO) 14630, the general requirements standard for nonactive surgical implants, is currently being revised to include information about MR safety of passive implants and to reference the ASTM standards. To address the unique safety issues of active implants, and in particular, active implants with leads, like pacemakers and neurostimulators, a joint working group between ISO TC150/SC6 on active implants and International Electrotechnical Commission (IEC) SC 62B MT40 on magnetic resonance equipment for medical diagnosis is working to develop a technical specification for active implantable medical devices (AIMDs) in MRI. While much progress has been made, work still needs to continue to develop a complete body of test methods to allow the evaluation of the safety of medical devices in the MR environment. J. Magn. Reson. Imaging 2007;26:1186–1189. © 2007 Wiley‐Liss, Inc.
A prototype RF dosimeter for independent measurement of the average specific absorption rate (SAR) during MRI
Authors: Stralka John P , Bottomley Paul A 
Published: October 2007

AbstractPurposeTo develop a scanner‐independent dosimeter for measuring the average radio frequency (RF) power deposition and specific absorption rates (SAR) for human MRI exposure.Materials and MethodsA prototype dosimeter has a transducer with orthogonal conducting loops surrounding a small signal‐generating MRI sample. The loops contain resistors whose values are adjusted to load the scanner's MRI coils equivalent to an average head or body during MRI. The scanner adjusts its power output to normal levels during setup, using the MRI sample. Following calibration, the total power and average SAR deposited in the transducer are measured from the root‐mean‐square (rms) power induced in the transducer during MRI.ResultsA 1.5 Tesla head transducer was adjusted to elicit the same load as the average of nine adult volunteers. Once adjusted, the transducer loads other head coils the same as the head does. The dosimeter is calibrated at up to 20 W total deposited power and 4.5 W/kg SAR in the average head, with about 5% accuracy.ConclusionThis dosimeter provides a simple portable means of measuring the power deposited in a body‐equivalent sample load, independent of the scanner. Further work will develop SAR dosimetry for the torso and for higher fields. J. Magn. Reson. Imaging 2007;26:1296–1302. © 2007 Wiley‐Liss, Inc.
Pooled analyses of effects on visual and visuomotor performance from exposure to magnetic stray fields from MRI scanners: Application of the Bayesian framework
Authors: de Vocht Frank , Glover Paul , Engels Hans , Kromhout Hans 
Published: October 2007

AbstractPurposeTo pool measurement data from individual studies on acute and temporal neurobehavioral effects of stray fields and reanalyze these using a Bayesian framework.Materials and MethodsData from tests assessing effects of exposure to stray fields (<1600 mT) from MRI systems (1.5–7.0 T) on visuomotor and visual sensory systems collected in three relatively small case‐crossover studies of volunteers seated in the magnet stray field were analyzed together using hierarchical regression models. Bayesian prior distributions were specified such that a priori an association with electromagnetic field (EMF) exposure was absent, and were updated with measurement data into posterior distributions.ResultsThe posterior distributions suggested that visuomotor speed, but not precision, was affected by exposure (−0.2% to −0.7% per 100 mT). The visual contrast threshold at stronger contrasts also increased with increased EMF exposure (−1%/100 mT).ConclusionUsing a Bayesian framework with conservative priors appeared to be an effective technique to assess subtle effects of exposure to stray magnetic fields. The posterior distributions were dominated by the observed data, which provides additional compelling evidence that the visuomotor domain and the visual contrast threshold level are negatively affected in the presence of stray fields of 1.5‐T to 7.0‐T MRI systems. J. Magn. Reson. Imaging 2007;26:1255–1260. © 2007 Wiley‐Liss, Inc.
Do static or time‐varying magnetic fields in magnetic resonance imaging (3.0 T) alter protein–gene expression?—A study on human embryonic lung fibroblasts
Authors: Schwenzer Nina F. , Bantleon Rüdiger , Maurer Brigitte , Kehlbach Rainer , Schraml Christina , Claussen Claus D. , Rodegerdts Enno 
Published: October 2007

AbstractPurposeTo evaluate the influence of magnetic resonance imaging (MRI) on gene expression in embryonic human lung fibroblasts (Hel 299).Materials and MethodsThe cells were exposed to the static magnetic field and to a turbo spin‐echo sequence of an MR scanner at 3.0 Tesla. An MR group (exposed) and a control group (sham‐exposed) were set up using a special MR‐compatible incubation system. The exposure time was two hours. Gene expression profiles were studied using a complementary deoxyribonucleic acid (cDNA) microarray containing 498 known genes involved in transcription, intracellular transport, structure/junction/adhesion or extracellular matrix, signaling, host defense, energetics, metabolism, cell shape, and death.ResultsNo changes in gene expression were found in either group (exposed or sham‐exposed cells) at the end of a two‐hour exposure for any of the 498 tested protein genes.ConclusionThe results suggest that MRI has no influence on protein–gene expression in eugenic human lung cells. J. Magn. Reson. Imaging 2007;26:1210–1215. © 2007 Wiley‐Liss, Inc.
A novel method for measuring the torque on implantable cardiovascular devices in MR static fields
Authors: D'Avenio Giuseppe , Canese Rossella , Podo Franca , Grigioni Mauro 
Published: October 2007

AbstractPurposeTo propose a novel quantitative method for measuring the torque acting on mechanical heart valve prostheses subjected to a high static magnetic field in a MR scanner.Materials and MethodsTorque measurements were performed with a torsion balance, implemented with a copper wire. The reaction torque exerted by the static magnetic field on the device was measured optically from the deflection angle of a laser beam spot on a graduate scale. Three different types of mechanical valves (two bileaflet and one monoleaflet) were tested at different locations of a small bore 4.7 tesla system.ResultsThe method proved to be particularly sensitive (detectability limit lower than 10−6 N · m), reliable and yielded quantitative reproducible results. The equivalent force of the torque measured for the three valves was at least 103‐fold lower than the force exerted by the beating heart.ConclusionThe proposed method provides a quantitative evaluation of the torque induced on prosthetic device by a MR scanner operating at high magnetic field. J. Magn. Reson. Imaging 2007;26:1368–1374. © 2007 Wiley‐Liss, Inc.
Patient safety concept for multichannel transmit coils
Authors: Seifert Frank , Wübbeler Gerd , Junge Sven , Ittermann Bernd , Rinneberg Herbert 
Published: October 2007

AbstractPurposeTo propose and illustrate a safety concept for multichannel transmit coils in MRI based on finite‐differences time‐domain (FDTD) simulations and validated by measurements.Materials and MethodsFDTD simulations of specific absorption rate (SAR) distributions in a cylindrical agarose phantom were carried out for various radio frequency (RF) driving conditions of a four‐element coil array. Additionally, maps of transmit amplitude, signal phase, and temperature rise following RF heating were measured by MRI.ResultsQuantitative agreement was achieved between simulated and measured field distributions, thus validating the numerical modeling. When applying the same RF power to each element of the coil array but systematically varying the RF phase between its elements, the maximum of the SAR distribution was found to vary by a factor of about 15.ConclusionOur results demonstrate that current RF safety approaches are inadequate to deal with the new challenge of multichannel transmit coils. We propose a new concept based on a systematic investigation of the parameter space for RF phases and amplitudes. In this way the driving conditions generating the highest local SAR values per unit power can be identified and appropriately considered in the RF safety concept of a given MRI system. J. Magn. Reson. Imaging 2007;26:1315–1321. © 2007 Wiley‐Liss, Inc.
Observation of changes in neural activity due to the static magnetic field of an MRI scanner
Authors: Toyomaki Atsuhito , Yamamoto Toru 
Published: October 2007

AbstractPurposeTo clarify whether a strong static magnetic field affects brain activity such as arousal level.Materials and MethodsWe compared the electroencephalography (EEG) inside an MRI scanner in the presence/absence of the static magnetic field in two different arousal levels of task and rest conditions. Cardiac‐related pulsations of head and blood flow induce an electric voltage at each EEG electrode in a static magnetic field. This induced voltage overlaps with the intrinsic EEG signal and becomes a large confounding factor. To extract the information of the intrinsic EEG from the contaminated EEG data measured in a static magnetic field, we developed a new analysis method.ResultsNo significant difference was observed in the intrinsic EEG in the absence of a magnetic field, whereas in the presence of the static magnetic field, the theta frequency band of the intrinsic EEG increased, especially during the task condition, but other frequency bands did not change.ConclusionOur results demonstrate that a static magnetic field affects brain activity. J. Magn. Reson. Imaging 2007;26:1216–1221. © 2007 Wiley‐Liss, Inc.
Occupational exposure to static and time‐varying gradient magnetic fields in MR units
Authors: Bradley Jill K. , Nyekiova Matilda , Price David L. , Lopez Lindsay D'jon , Crawley Therese 
Published: October 2007

AbstractPurposeTo assess exposure of MR staff to static and time‐varying gradient magnetic fields by direct measurement and questionnaire and to compare these to the action values and exposure limits stated in published guidance.Materials and MethodsInstantaneous and time‐averaged exposure to static magnetic fields were measured on clinical and research MR scanners. A questionnaire was sent to 100 clinical MR centers to estimate the average static field exposure. Instantaneous measurements of the time‐varying magnetic field were conducted on a 1.5T conventional and a 0.6T open‐bore MR system.ResultsThe 24‐hour time‐averaged static field exposure was measured to be 1.8 ± 1 mT and the questionnaire produced a 24‐hour time‐average of 2.3 mT. The maximum static field strength recorded during patient set up was 554 mT. Time‐varying gradient field exposure was found to exceed the action values up to 30 cm from the bore entrance or magnet rim.ConclusionThe time‐varying gradient field exposure limit is the only limit to be exceeded. The time‐averaged static field exposure to staff was found to be 100 times lower than the recommended guidelines. J. Magn. Reson. Imaging 2007;26:1204–1209. © 2007 Wiley‐Liss, Inc.
British association of MR radiographers (BAMRR) safety survey 2005: Potential impact of European Union (EU) Physical Agents Directive (PAD) on electromagnetic fields (EMF)
Authors: Moore Elizabeth A. , Scurr Erica D. 
Published: October 2007

AbstractPurposeTo measure the potential impact on clinical MRI practice in the UK of the European Union (EU) Physical Agents Directive (PAD) on electromagnetic fields (EMF). There is evidence that the exposure limit values contained in the PAD will make it impossible for members of staff to stand close to the magnet during scanning; currently this is common practice in order to provide care and support for vulnerable patients. Interventional MR procedures will also be impossible.Materials and MethodsMembers of the British Association of MR Radiographers (BAMRR) were sent a questionnaire to assess the impact of the PAD and related safety issues.ResultsA total of 25% of responding sites have at least one sedation/general anesthesia (GA) session per week, while only 3% reported any interventional practice. A total of 29% of respondents reported that operators give a bolus injection by hand during contrast‐enhanced magnetic resonance angiography (CE‐MRA) scans. Overall it is estimated that 3% of all MR examinations in the UK are performed with a staff member in the magnet room. Some of these examinations would be impossible without staff in the room and it would be necessary for patients to have computed tomography (CT) instead of MRI. The additional radiation dose of substituting CT for MRI is estimated at 224 man‐sievert per year.ConclusionWhile the financial costs of implementing the PAD (EMF) are relatively low, the social costs are difficult to quantify but potentially more alarming. J. Magn. Reson. Imaging 2007;26:1303–1307. © 2007 Wiley‐Liss, Inc.
Measurement of visual evoked potential during and after periods of pulsed magnetic field exposure
Authors: Glover Paul M. , Eldeghaidy Sally , Mistry Tejal R. , Gowland Penny A. 
Published: October 2007

AbstractPurposeTo study the effect of switched magnetic fields used in MR scanners on the visual evoked potential (VEP) in human subjects.Materials and MethodsWe have used an MRI gradient coil, remote from an MRI magnet to produce a time‐varying magnetic field (0.5 kHz, peak field ∼8.7 T/second) in the human brain without the confounding effects of static field exposure or accompanying acoustic noise. The VEP response to a 2‐Hz reversal, 8 × 8 checkerboard, occupying 20 degrees of the visual field was recorded from occipital locations O1 and O2. VEP recordings were made every five minutes before, during, and after a 10‐minute magnetic field exposure period for seven subjects.ResultsIn contradiction to studies previously reported in the literature for fields of 50 Hz and 60 mT, no significant effects on the peak amplitude or latency of the VEP P100 O1 and O2 responses were found.ConclusionSwitched magnetic fields of a level and frequency comparable to those used in MRI do not have a significant effect on primary retinal or visual processing. J. Magn. Reson. Imaging 2007;26:1353–1356. © 2007 Wiley‐Liss, Inc.
Tissue warming and regulatory responses induced by radio frequency energy deposition on a whole‐body 3‐Tesla magnetic resonance imager
Authors: Boss Andreas , Graf Hansjörg , Berger Alexander , Lauer Ulrike A. , Wojtczyk Hanne , Claussen Claus D. , Schick Fritz 
Published: October 2007

AbstractPurposeTo quantify the B1‐field induced tissue warming on a 3T‐whole‐body scanner, to test whether the patient is able to sense the temperature change, and to evaluate whether the imaging procedure constitutes a significant cardiovascular stress.Materials and MethodsA total of 18 volunteers were divided into three equal groups for 3.0T MRI of the pelvis, the head, or the knee. An imaging protocol operating at first level mode was applied, allowing radio frequency (RF) irradiation up to the legal specific absorption rate (SAR) limits. An identical placebo protocol with active gradient switching but without RF transmission was used. Temperature changes were measured with a fiber‐optic thermometer (FO) and an infrared camera (IR).ResultsTemperature differences to the placebo were highest for imaging of the pelvis (FO: ΔT = 0.88 ± 0.13°C, IR: ΔT = 1.01 ± 0.15°C) as compared to the head (FO: ΔT = 0.46 ± 0.12°C, IR: ΔT = 0.47 ± 0.10°C) and the knee (FO: ΔT = 0.33 ± 0.11°C, IR: ΔT = 0.37 ± 0.09°C). The volunteers were able to discriminate between imaging and placebo for pelvic (P < 0.0001) and head (P = 0.0005) imaging but not for knee imaging (P = 0.209). No changes in heart rate or blood pressure were detected.ConclusionThe 3.0T MRI in the first operational mode may lead to measurable and perceptible thermal energy deposition. However, it may be regarded as safe concerning the thermoregulatory cardiovascular stress. J. Magn. Reson. Imaging 2007;26:1334–1339. © 2007 Wiley‐Liss, Inc.
Heating of metallic implants and instruments induced by gradient switching in a 1.5‐Tesla whole‐body unit
Authors: Graf Hansjörg , Steidle Günter , Schick Fritz 
Published: October 2007

AbstractPurposeTo examine gradient switching–induced heating of metallic parts.Materials and MethodsCopper and titanium frames and sheets (≈50 × 50 mm2, 1.5 mm thick, frame width = 3 mm) surrounded by air were positioned in the scanner perpendicular to the static field horizontally 20 cm off‐center. During the execution of a sequence (three‐dimensional [3D] true fast imaging with steady precession [True‐FISP], TR = 6.4 msec) exploiting the gradient capabilities (maximum gradient = 40 mT/m, maximum slew rate = 200 T/m/second), heating was measured with an infrared camera. Radio frequency (RF) amplitude was set to zero volts. Heating of a copper frame with a narrowing to 1 mm over 20 mm at one side was examined in air and in addition surrounded by several liters of gelled saline using fiber‐optic thermography. Further heating studies were performed using an artificial hip made of titanium, and an aluminum replica of the hip prosthesis with the same geometry.ResultsFor the copper specimens, considerable heating (>10°C) in air and in gelled saline (>1.2°C) could be observed. Heating of the titanium specimens was markedly less (≈1°C in air). For the titanium artificial hip no heating could be detected, while the rise in temperature for the aluminum replica was approximately 2.2°C.ConclusionHeating of more than 10°C solely due to gradient switching without any RF irradiation was demonstrated in isolated copper wire frames. Under specific conditions (high gradient duty cycle, metallic loop of sufficient inductance and low resistance, power matching) gradient switching–induced heating of conductive specimens must be considered. J. Magn. Reson. Imaging 2007;26:1328–1333. © 2007 Wiley‐Liss, Inc.
Calculation of MRI‐induced heating of an implanted medical lead wire with an electric field transfer function
Authors: Park Sung‐Min , Kamondetdacha Rungkiet , Nyenhuis John A. 
Published: October 2007

AbstractPurposeTo develop and demonstrate a method to calculate the temperature rise that is induced by the radio frequency (RF) field in MRI at the electrode of an implanted medical lead.Materials and MethodsThe electric field near the electrode is calculated by integrating the product of the tangential electric field and a transfer function along the length of the lead. The transfer function is numerically calculated with the method of moments. Transfer functions were calculated at 64 MHz for different lengths of model implants in the form of bare wires and insulated wires with 1 cm of wire exposed at one or both ends.ResultsHeating at the electrode depends on the magnitude and the phase distribution of the transfer function and the incident electric field along the length of the lead. For a uniform electric field, the electrode heating is maximized for a lead length of approximately one‐half a wavelength when the lead is terminated open. The heating can be greater for a worst‐case phase distribution of the incident field.ConclusionThe transfer function is proposed as an efficient method to calculate MRI‐induced heating at an electrode of a medical lead. Measured temperature rises of a model implant in a phantom were in good agreement with the rises predicted by the transfer function. The transfer function could be numerically or experimentally determined. J. Magn. Reson. Imaging 2007;26:1278–1285. © 2007 Wiley‐Liss, Inc.