A field camera for MR sequence monitoring and system analysis

Dietrich, Benjamin E.; Brunner, David O.; Wilm, Bertram J.; Barmet, Christoph; Gross, Simon; Kasper, Lars; Haeberlin, Maximilian; Schmid, Thomas; Vannesjo, S. Johanna; Pruessmann, Klaas P.

doi:10.1002/mrm.25770

Cited by 97 publications

(120 citation statements)

References 20 publications

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“…Otherwise, RF recording readily lends itself to continuous operation and thus forms an attractive complement to continuous measurement of low-to audio frequency magnetic fields. A combined continuous monitoring system was created by extension and modification of the stand-alone field camera design previously described in [13]. In terms of hardware the key additions and changes concern the probehead design, front-end module, and sequencing provisions for rapid and optionally alternating re-excitation, and simultaneous 1 H and 19 F detection [14].…”

Section: A Conceptmentioning

confidence: 99%

“…As detailed in [13] the receiver hardware was based on a software-defined radio approach without analog frequency conversion. A first stage of electronics, comprising T/R switches, pre-amplifiers and excitation amplifiers was directly connected to the field probe array for placement inside the magnet bore ( Fig.…”

Section: Transmit/receive Hardwarementioning

confidence: 99%

“…[13] a direct digital synthesis (DDS) pulse synthesizer module was used to generate probe excitation pulses (second stage in Fig. 1).…”

Section: Transmit/receive Hardwarementioning

confidence: 99%

“…Field effect transistor (FET)-based T/R switches were used to achieve submicrosecond switching performance [13].…”

Section: Transmit/receive Hardwarementioning

confidence: 99%

“…Using 19 F [9][10][11] or 2 H [12] as probe nuclei permits such field measurement concurrently with 1 H imaging, relying on spectral decoupling. For system diagnostics it can rely on a dedicated spectrometer, forming a stand-alone system [13]. A dedicated system has also been used to achieve combined gradient and RF pulse monitoring, relying on non-proton probes, dual-frequency reception and suitable signal scaling [14].…”

Section: Introductionmentioning

confidence: 99%

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Continuous Magnetic Field Monitoring Using Rapid Re-Excitation of NMR Probe Sets

Dietrich

Brunner

Wilm

et al. 2016

IEEE Trans. Med. Imaging

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MRI relies on static and spatially varying dynamic magnetic fields of high accuracy. NMR field probes permit the direct observation of spatiotemporal field dynamics for diverse purposes such as data correction, field control, sequence validation, and hardware characterization. However, due to probe signal decay and dephasing existing field cameras are limited in terms of readout duration and the extent of k -space that can be covered. The present work aims to overcome these limitations by the transition to short-lived NMR probes and rapid re-excitation. The proposed approach uses probes with T 2 so short that thermal relaxation dominates signal decay even in the presence of strongest gradients. They are integrated with transmit, receive and sequencing electronics that permit high-rate re-excitation with optional probe alternation as well as complementary RF pulse recording. The system is demonstrated by monitoring of sample MRI sequences with long readouts and large gradient moments. It is compared with the conventional long-lived probe concept and characterized in terms of net sensitivity and sources of systematic error. Continuous k -space trajectory mapping is demonstrated and validated by trajectory-based image reconstruction.

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Section: A Conceptmentioning

confidence: 99%

Section: Transmit/receive Hardwarementioning

confidence: 99%

“…[13] a direct digital synthesis (DDS) pulse synthesizer module was used to generate probe excitation pulses (second stage in Fig. 1).…”

Section: Transmit/receive Hardwarementioning

confidence: 99%

“…Field effect transistor (FET)-based T/R switches were used to achieve submicrosecond switching performance [13].…”

Section: Transmit/receive Hardwarementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Continuous Magnetic Field Monitoring Using Rapid Re-Excitation of NMR Probe Sets

Dietrich

Brunner

Wilm

et al. 2016

IEEE Trans. Med. Imaging

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General purpose electronics for real‐time processing and encoding of non‐MR data in MR acquisitions

Pedersen

Hanson²,

Xue

et al. 2018

Concepts Magn Reson

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Recording of data other than MR signals are often of interest during MRI. We present unique, versatile circuitry developed for sampling and real-time processing of such non-MR signals to facilitate recording of these by an MR scanner. The circuitry is capable of acquiring multiple signals at 200 kHz sampling rate, measure RF power correlates, perform fast and flexible signal processing, and transmitting both amplitude and frequency modulated RF signals receivable by MR scanners. As an example of use, an electronic point-source signal is generated by the circuitry, and transmitted wirelessly to the receive coil of an MR scanner during an echo planar imaging sequence.

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Quality and denoising in real‐time functional magnetic resonance imaging neurofeedback: A methods review

Heunis

Lamerichs

Zinger

et al. 2020

Human Brain Mapping

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Neurofeedback training using real‐time functional magnetic resonance imaging (rtfMRI‐NF) allows subjects voluntary control of localised and distributed brain activity. It has sparked increased interest as a promising non‐invasive treatment option in neuropsychiatric and neurocognitive disorders, although its efficacy and clinical significance are yet to be determined. In this work, we present the first extensive review of acquisition, processing and quality control methods available to improve the quality of the neurofeedback signal. Furthermore, we investigate the state of denoising and quality control practices in 128 recently published rtfMRI‐NF studies. We found: (a) that less than a third of the studies reported implementing standard real‐time fMRI denoising steps, (b) significant room for improvement with regards to methods reporting and (c) the need for methodological studies quantifying and comparing the contribution of denoising steps to the neurofeedback signal quality. Advances in rtfMRI‐NF research depend on reproducibility of methods and results. Notably, a systematic effort is needed to build up evidence that disentangles the various mechanisms influencing neurofeedback effects. To this end, we recommend that future rtfMRI‐NF studies: (a) report implementation of a set of standard real‐time fMRI denoising steps according to a proposed COBIDAS‐style checklist ( https://osf.io/kjwhf/ ), (b) ensure the quality of the neurofeedback signal by calculating and reporting community‐informed quality metrics and applying offline control checks and (c) strive to adopt transparent principles in the form of methods and data sharing and support of open‐source rtfMRI‐NF software. Code and data for reproducibility, as well as an interactive environment to explore the study data, can be accessed at https://github.com/jsheunis/quality‐and‐denoising‐in‐rtfmri‐nf.

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A field camera for MR sequence monitoring and system analysis

Abstract: A flexible and versatile monitoring system is presented, delivering camera-like access to otherwise hardly accessible field dynamics with nanotesla resolution. Its stand-alone nature enables field analysis even during unknown MR system states.

Cited by 97 publications

References 20 publications

Continuous Magnetic Field Monitoring Using Rapid Re-Excitation of NMR Probe Sets

Continuous Magnetic Field Monitoring Using Rapid Re-Excitation of NMR Probe Sets

General purpose electronics for real‐time processing and encoding of non‐MR data in MR acquisitions

Quality and denoising in real‐time functional magnetic resonance imaging neurofeedback: A methods review

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