Controlling radiofrequency-induced currents in guidewires using parallel transmit

Etezadi-Amoli, Maryam; Stang, Pascal; Kerr, Adam B.; Pauly, John M.; Scott, Greig

doi:10.1002/mrm.25543

Cited by 50 publications

(111 citation statements)

References 36 publications

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“…Medusa has also enabled Parallel Transmit research in predistortion methods [24] and Cartesian Feedback for RF power amplifier linearization [27], [28], and impedance characterization of RF amplifiers [23] and coils [25]. Finally, Medusa is used for interventional research addressing therapeutic RF ablation [30] as well as MR guidewire safety through reverse polarization imaging [26] and active current cancellation [29]. …”

Section: Discussionmentioning

confidence: 99%

Medusa: A Scalable MR Console Using USB

Stang

Conolly

Santos

et al. 2012

IEEE Trans. Med. Imaging

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MRI pulse sequence consoles typically employ closed proprietary hardware, software, and interfaces, making difficult any adaptation for innovative experimental technology. Yet MRI systems research is trending to higher channel count receivers, transmitters, gradient/shims, and unique interfaces for interventional applications. Customized console designs are now feasible for researchers with modern electronic components, but high data rates, synchronization, scalability, and cost present important challenges. Implementing large multi-channel MR systems with efficiency and flexibility requires a scalable modular architecture. With Medusa, we propose an open system architecture using the Universal Serial Bus (USB) for scalability, combined with distributed processing and buffering to address the high data rates and strict synchronization required by multi-channel MRI. Medusa uses a modular design concept based on digital synthesizer, receiver, and gradient blocks, in conjunction with fast programmable logic for sampling and synchronization. Medusa is a form of synthetic instrument, being reconfigurable for a variety of medical/scientific instrumentation needs. The Medusa distributed architecture, scalability, and data bandwidth limits are presented, and its flexibility is demonstrated in a variety of novel MRI applications.

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Section: Discussionmentioning

confidence: 99%

Medusa: A Scalable MR Console Using USB

Stang

Conolly

Santos

et al. 2012

IEEE Trans. Med. Imaging

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“…A degree of control over the emitted electromagnetic fields is possible with parallel transmit (PTx) array coils. It has been shown that RF‐induced current “modes” may exist on the guidewire and can be determined by 1 or more current sensors placed over the guidewire . Typically, 1 or more maximum current modes (MM) in which the PTx system produces a strong current on the conductor exist, along with additional null current modes (NM) in which RF excitation produces 0 measured current at the sensor’s location.…”

Section: Introductionmentioning

confidence: 99%

Safe guidewire visualization using the modes of a PTx transmit array MR system

Godinez

Scott

Padormo

et al. 2019

Magnetic Resonance in Med

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Purpose MRI‐guided cardiovascular intervention using standard metal guidewires can produce focal tissue heating caused by induced radiofrequency guidewire currents. It has been shown that safe operation is made possible by using parallel transmit radiofrequency coils driven in the null current mode, which does not induce radiofrequency currents and hence allows safe tissue visualization. We propose that the maximum current modes, usually considered unsafe, be used at very low power levels to visualize conductive wires, and we investigate pulse sequences best suited for this application. Methods Spoiled gradient echo, balanced steady‐state free precession, and turbo spin echo sequences were evaluated for their ability to visualize a conductive guidewire embedded in a gel phantom when run in maximum current modes at very low power level. Temperature at the guidewire tip was monitored for safety assessment. Results Excellent guidewire visualization could be achieved using maximum current modes excitation, with the turbo spin echo sequence giving the best image quality. Although turbo spin echo is usually considered to be a high‐power sequence, our method reduced all pulses to 1% amplitude (0.01% power), and heating was not detected. In addition, visualization of background tissue can be achieved using null current mode, also with no recorded heating at the guidewire tip even when running at 100% (reported) specific absorption rate. Conclusion Parallel transmit is a promising approach for both guidewire and tissue visualization using maximum and null current modes, respectively, for interventional cardiac MRI. Such systems can switch excitation mode instantaneously, allowing for flexible integration into interactive sequences.

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“…The problem of heating due to the RF field, especially with regard to the interaction with implanted devices, is a good case in point. For example, a variety of techniques have been developed to defeat the antenna effect, by engineering wires and cables to be safer, or making changes to the RF transmit . More general solutions to the SAR problem have involved pulse sequence and RF pulse modifications .…”

Section: Discussionmentioning

confidence: 99%

The physics of MRI safety

Panych

Madore

2017

Magnetic Resonance Imaging

123

144

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The main risks associated with magnetic resonance imaging (MRI) have been extensively reported and studied; for example, everyday objects may turn into projectiles, energy deposition can cause burns, varying fields can induce nerve stimulation, and loud noises can lead to auditory loss. The present review article is geared toward providing intuition about the physical mechanisms that give rise to these risks. On the one hand, excellent literature already exists on the practical aspect of risk management, with clinical workflow and recommendations. On the other hand, excellent technical articles also exist that explain these risks from basic principles of electromagnetism. We felt that an underserved niche might be found between the two, ie, somewhere between basic science and practical advice, to help develop intuition about electromagnetism that might prove of practical value when working around MR scanners. Following a wide‐ranging introduction, risks originating from the main magnetic field, the excitation RF electromagnetic field, and switching of the imaging gradients will be presented in turn. Level of Evidence: 5 Technical Efficacy: 1 J. Magn. Reson. Imaging 2018;47:28–43.

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Controlling radiofrequency-induced currents in guidewires using parallel transmit

Cited by 50 publications

References 36 publications

Medusa: A Scalable MR Console Using USB

Medusa: A Scalable MR Console Using USB

Safe guidewire visualization using the modes of a PTx transmit array MR system

The physics of MRI safety

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