Regarding the Value Reported for the Term “Spatial Gradient Magnetic Field” and How This Information Is Applied to Labeling of Medical Implants and Devices

Shellock, Frank G.; Kanal, Emanuel; Gilk, Tobias

doi:10.2214/ajr.10.5004

Cited by 47 publications

(45 citation statements)

References 2 publications

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“…Of the two magnetic fields in MPI, the selection field is comparable to the field gradients just outside the homogeneous region of an MRI scanner. In fact, a commercially available 3T MRI scanner was shown to have a strong 7.2 T/m maximum spatial gradient right outside its imaging bore [7], comparable to the 7 T/m selection field of our MPI scanner described in [8]. Therefore, just as the field in MRI, the selection field in MPI creates the risk of ferromagnetic objects being pulled into the scanner.…”

mentioning

confidence: 75%

Magnetostimulation Limits in Magnetic Particle Imaging

Sarıtaş

Goodwill

Zhang

et al. 2013

IEEE Trans. Med. Imaging

141

174

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For magnetic particle imaging (MPI), specific absorption rate (SAR) and more critically magnetostimulation (i.e., dB/dt) safety limits will determine the optimal scan parameters, such as the drive field strength and frequency. These parameters will impact the scanning speed, field-of-view (FOV) and signal-to-noise ratio in MPI. Understanding the potential safety hazards of the drive field is critical for scaling MPI for human use. In this work, we demonstrate that magnetostimulation is the primary magnetic safety consideration in MPI, and we describe the first human-subject magnetostimulation threshold experiments for MPI using homogeneous coils. Our experiments, performed on the arm and leg, indicate that magnetostimulation thresholds monotonically decrease with increasing frequency. Additionally, we show for the first time that a strong inverse correlation exists between the threshold and the body part size. The chronaxie time, on the other hand, did not vary with body part size. We conclude with an estimation of the magnetostimulation thresholds for a full-body MPI scanner: a mean asymptotic threshold of 14.3 mT-pp (peak-to-peak) with a mean chronaxie time of 289 μs, which correspond to a magnetostimulation threshold of about 15 mT-pp for frequencies between 25 and 50 kHz. These findings will have a great impact on the optimization of MPI parameters, especially in determining the number of partial FOVs required to cover a region of interest.

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mentioning

confidence: 75%

Magnetostimulation Limits in Magnetic Particle Imaging

Sarıtaş

Goodwill

Zhang

et al. 2013

IEEE Trans. Med. Imaging

141

174

View full text Add to dashboard Cite

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“…Using this shielding technique generates a spatial gradient of the static magnetic field B 0 in which the attraction force is exponentially increased. The spatial gradient of the gradient coil is a time-varying magnetic field generated by the coils for spatial encoding of the MRI signals during scanning [16].…”

Section: Theoretical Evaluationmentioning

confidence: 99%

Quantification of Force and Torque Applied by a High-Field Magnetic Resonance Imaging System on an Ultrasonic Motor for MRI-Guided Robot-Assisted Interventions

2017

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Abstract:The risk of accidental dislodgement of robot-operated surgical mechanisms can lead to morbidity or mortality. The force and torque applied by a 3.0-tesla scanner on an ultrasonic motor are not fully known. The force and torque may displace the motor, which is not fully magnetic resonance imaging (MRI)-compatible but can be safely used in MR environments. A suspension apparatus was designed to measure the angles of deflection and rotation applied to the motor by MR magnetic fields. Three orientations and two power states of the motor were assessed inside the MR bore. The displacement force and torque were measured at eight locations with respect to the bore. The displacement force on the motor from 10 cm outside the magnet bore to 20 cm inside the bore ranged from 3 to 7 gF. The experimental measurements are in agreement with the theoretical values. Running the motor altered the force by 1 gF. The force does not significantly change when the MRI scanner is on. Considerable displacement force is applied to the motor, and no deflection torque is observed. Quantified values can be used to solve dynamic equations for robotic mechanisms intended for MRI-guided operations.

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“…Additionally, ferromagnetic implants may move or even dislodge causing pain and injury to the patients. [40][41][42] …”

Section: Diagnostic Imaging Techniquementioning

confidence: 99%