The rf coil as a sensitive motion detector for magnetic resonance imaging

Buikman, D.; Helzel, T.; Röschmann, P.

doi:10.1016/0730-725x(88)90403-1

Cited by 28 publications

(34 citation statements)

References 4 publications

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“…Despite this low power, the impedance of the coil reflects critical electromagnetic properties of its load. Impedance fluctuations are sufficiently sensitive to detect pulse rate and respiratory motion , and have also been applied to the detection of potentially RF‐unsafe devices and conditions. .…”

Section: Introductionmentioning

confidence: 99%

Offline impedance measurements for detection and mitigation of dangerous implant interactions: An RF safety prescreen

et al. 2014

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Purpose The concept of an “RF Safety Prescreen” is investigated, wherein dangerous interactions between RF fields used in MRI, and conductive implants in patients are detected through impedance changes in the RF coil. Theory The behavior of coupled oscillators is reviewed, and the resulting, observable impedance changes are discussed. Methods A birdcage coil is loaded with a static head phantom and a wire phantom with a wire close to its resonant length, the shape, position and orientation of which can be changed. Interactions are probed with a current sensor and network analyzer. Results Impedance spectra show dramatic, unmistakable splitting in cases of strong coupling, and strong correlation is observed between induced current and scattering parameters. Conclusions The feasibility of a new, low-power prescreening technique has been demonstrated in a simple phantom experiment, which can unambiguously detect resonant interactions between an implanted wire and an imaging coil. A new technique has also been presented which can detect parallel transmit null modes for the wire.

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Section: Introductionmentioning

confidence: 99%

Offline impedance measurements for detection and mitigation of dangerous implant interactions: An RF safety prescreen

et al. 2014

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“…Cardiac motion has been addressed by synchronization strategies exploiting (i) finger plethysmography[1], (ii) cardiac activity related esophageal wall motion[2], (iii) invasive left ventricular blood pressure gating[3], (iv) Doppler ultrasound[4], (v) motion induced changes in the impedance match of RF-coils[5], (vi) self gating techniques[6-10] and optic acoustic methods [11] including human and animal studies. In current clinical CMR, cardiac motion is commonly dealt with using electrocardiographic (ECG) or finger pulse oximetry (POX) triggering/gating techniques [12-14] to synchronize data acquisition with the cardiac cycle.…”

Section: Introductionmentioning

confidence: 99%

Acoustic cardiac triggering: a practical solution for synchronization and gating of cardiovascular magnetic resonance at 7 Tesla

Frauenrath

Hezel

Renz

et al. 2010

Journal of Cardiovascular Magnetic Resonance

107

110

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BackgroundTo demonstrate the applicability of acoustic cardiac triggering (ACT) for imaging of the heart at ultrahigh magnetic fields (7.0 T) by comparing phonocardiogram, conventional vector electrocardiogram (ECG) and traditional pulse oximetry (POX) triggered 2D CINE acquisitions together with (i) a qualitative image quality analysis, (ii) an assessment of the left ventricular function parameter and (iii) an examination of trigger reliability and trigger detection variance derived from the signal waveforms.ResultsECG was susceptible to severe distortions at 7.0 T. POX and ACT provided waveforms free of interferences from electromagnetic fields or from magneto-hydrodynamic effects. Frequent R-wave mis-registration occurred in ECG-triggered acquisitions with a failure rate of up to 30% resulting in cardiac motion induced artifacts. ACT and POX triggering produced images free of cardiac motion artefacts. ECG showed a severe jitter in the R-wave detection. POX also showed a trigger jitter of approximately Δt = 72 ms which is equivalent to two cardiac phases. ACT showed a jitter of approximately Δt = 5 ms only. ECG waveforms revealed a standard deviation for the cardiac trigger offset larger than that observed for ACT or POX waveforms.Image quality assessment showed that ACT substantially improved image quality as compared to ECG (image quality score at end-diastole: ECG = 1.7 ± 0.5, ACT = 2.4 ± 0.5, p = 0.04) while the comparison between ECG vs. POX gated acquisitions showed no significant differences in image quality (image quality score: ECG = 1.7 ± 0.5, POX = 2.0 ± 0.5, p = 0.34).ConclusionsThe applicability of acoustic triggering for cardiac CINE imaging at 7.0 T was demonstrated. ACT's trigger reliability and fidelity are superior to that of ECG and POX. ACT promises to be beneficial for cardiovascular magnetic resonance at ultra-high field strengths including 7.0 T.

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“…Piezoelectric or ultrasound detections of respiratory motion have been proposed for applications in animals (24). Cardiac and respiration motion can also be detected directly on the reflected power measured on the RF coil (25). Navigator echoes can be acquired before motion-dependent MR sequences and contain information on the displacement of the diaphragm (26).…”

Section: Inspiration Expirationmentioning

confidence: 99%

Amplitude demodulation of the electrocardiogram signal (ECG) for respiration monitoring and compensation during MR examinations

Felblinger¹,

Boesch²

1997

Magnetic Resonance in Med

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A method for respiration monitoring during MR-sequences using the electrocardiogram signal (ECG) is presented. The basic principle is known in conventional patient monitoring and is based on the fact that the amplitude of the ECG-signal varies with respiratory motion. A demodulation of this "cardio-respiratory signal" yields a respiration curve that can be used for patient monitoring, triggering, or respiration compensation of MRI sequences. Since no drift is introduced by digital demodulation, this method is superior to analog signal processing. The proposed method was applied during MR examinations using an optically coupled ECG sensor that has the advantage of almost negligible interference due to the MR sequences (< < 10% of the main ECG signal). The respiration signal obtained is strongly correlated (r = 0.79 to 0.98) with the position of the diaphragm in inferior-superior direction measured during breath-holding MRI.

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The rf coil as a sensitive motion detector for magnetic resonance imaging

Cited by 28 publications

References 4 publications

Offline impedance measurements for detection and mitigation of dangerous implant interactions: An RF safety prescreen

Offline impedance measurements for detection and mitigation of dangerous implant interactions: An RF safety prescreen

Acoustic cardiac triggering: a practical solution for synchronization and gating of cardiovascular magnetic resonance at 7 Tesla

Amplitude demodulation of the electrocardiogram signal (ECG) for respiration monitoring and compensation during MR examinations

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