SQUID-based instrumentation for ultralow-field MRI

Zotev, Vadim; Matlashov, Andrei; Volegov, P. L.; Urbaitis, Algis V.; Espy, Michelle A.; Kraus, R.H.

doi:10.1088/0953-2048/20/11/s13

Cited by 90 publications

(78 citation statements)

References 25 publications

(42 reference statements)

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“…All experimental results, reported in this paper, were obtained using the seven-channel SQUID system for 3D ULF MRI and MEG [23,24], depicted schematically in Fig. 1.…”

Section: Instrumentationmentioning

confidence: 99%

“…1. The system includes seven second-order SQUID gradiometers with 37 mm diameter and 60 mm baseline, characterized by magnetic field resolutions of 1.2…2.8 fT/√Hz at 1 kHz [24]. The gradiometers are installed parallel to one another inside a flat-bottom liquid helium cryostat.…”

Section: Instrumentationmentioning

confidence: 99%

“…Recently, we used a seven-channel SQUID system [23,24], specially designed for MEG and ULF MRI, to acquire the first images of the human brain at microtesla fields [25]. We also recorded auditory MEG signals during the same imaging session [25].…”

Section: Introductionmentioning

confidence: 99%

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Parallel MRI at microtesla fields

Zotev

Volegov

Matlashov

et al. 2008

Journal of Magnetic Resonance

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Parallel imaging techniques have been widely used in high-field magnetic resonance imaging (MRI). Multiple receiver coils have been shown to improve image quality and allow accelerated image acquisition. Magnetic resonance imaging at ultra-low fields (ULF MRI) is a new imaging approach that uses SQUID (superconducting quantum interference device) sensors to measure the spatially encoded precession of pre-polarized nuclear spin populations at microtesla-range measurement fields. In this work, parallel imaging at microtesla fields is systematically studied for the first time. A seven-channel SQUID system, designed for both ULF MRI and magnetoencephalography (MEG), is used to acquire 3D images of a human hand, as well as 2D images of a large water phantom. The imaging is performed at 46 microtesla measurement field with pre-polarization at 40 mT. It is shown how the use of seven channels increases imaging field of view and improves signal-to-noise ratio for the hand images. A simple procedure for approximate correction of concomitant gradient artifacts is described. Noise propagation is analyzed experimentally, and the main source of correlated noise is identified. Accelerated imaging based on one-dimensional undersampling and 1D SENSE (sensitivity encoding) image reconstruction is studied in the case of the 2D phantom. Actual 3-fold imaging acceleration in comparison to single-average fully encoded Fourier imaging is demonstrated. These results show that parallel imaging methods are efficient in ULF MRI, and that imaging performance of SQUID-based instruments improves substantially as the number of channels is increased.

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“…All experimental results, reported in this paper, were obtained using the seven-channel SQUID system for 3D ULF MRI and MEG [23,24], depicted schematically in Fig. 1.…”

Section: Instrumentationmentioning

confidence: 99%

Section: Instrumentationmentioning

confidence: 99%

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Parallel MRI at microtesla fields

Zotev

Volegov

Matlashov

et al. 2008

Journal of Magnetic Resonance

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“…Ultra-low field nuclear magnetic resonance and magnetic resonance imaging (ULF-MR) utilizes a very weak magnetic field, in the order of μT, for its measurement field (B m ) that induces nuclear spin precession [1][2][3][4]. Such a low B m requires (1) a magnetic sensor with a flat frequency response down to as low as 100 Hz or less and (2) a strong prepolarization field (B p ) which magnetizes the sample prior to magnetic resonance measurement to enhance magnetic resonance signal [3].…”

Section: Introductionmentioning

confidence: 99%

Postmortem analysis of a failed liquid nitrogen-cooled prepolarization coil for SQUID sensor-based ultra-low field magnetic resonance

Hwang¹,

Kim²,

Hung³

et al. 2014

Progress in Superconductivity and Cryogenics

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A liquid nitrogen-cooled prepolarization (B p ) coil made for ultra-low field nuclear magnetic resonance and magnetic resonance imaging (ULF-MR) designed to generate 7 mT/A was fabricated. However, with suspected internal insulation failure, the coil was investigated in order to find out the source of the failure. This paper reports detailed build of the failed B p coil and a number of analysis methods utilized to figure out the source and the mode of failure. The analysis revealed that pyrolytic graphite sheet linings put on either sides of the coil for better thermal conduction acted as an electrical bridge between inner and outer layers of the coil to short out the coil whenever a moderately high voltage was applied across the coil. A simple model circuit simulation corroborated the analysis and further revealed that the failed insulation acted effectively as a damping resistor of R d,eff = 6 Ω across the coil. This damping resistance produced a 50 ms-long voltage tail after the coil current was ramped down, making the coil not suitable for use in ULF-MR, which requires complete removal of magnetic field from B p coil within milliseconds.

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“…Therefore, much effort has been devoted to design and develop optimized sensors and prototypes relying on superconducting devices. Indeed, recent studies have demonstrated the feasibility of low-field NMR/MRI detection based on Superconducting QUantum Interference Devices (SQUID), relying on a measurement magnetic field ∼ 100 µT combined with a pulsed prepolarizing field ∼ 10 to 100 mT [9,10]. The latter is needed to increase the magnetization of the sample and hence the signal strength.…”

Section: Introductionmentioning

confidence: 99%

NMR Detection at 8.9 Mt With a GMR Based Sensor Coupled to a Superconducting Nb Flux Transformer

Sinibaldi¹,

Luca²,

Nieminen³

et al. 2013

PIER

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Abstract-This study presents NMR signal detection by means of a superconducting channel consisting of a Nb surface detection coil inductively coupled to a YBCO mixed sensor. The NMR system operates at a low-field (8.9 mT) in a magnetically shielded room suitable for magnetoencephalographic (MEG) recordings. The main field is generated by a compact solenoid and the geometry of the pick-up coil has been optimized to provide high spatial sensitivity in the NMR field of view. The Nb detection coil is coupled to the mixed sensor through a Nb input coil. The mixed sensor consists of a superconducting YBCO loop with 2-µm constriction above which two Giant MagnetoResistance sensors are placed in a half-bridge configuration to detect changes of the bridge voltage as a function of the flux through the YBCO loop. The sensitivity of the receiving channel is calibrated experimentally. The measured spatial sensitivity is in agreement with the simulations and is ∼10 times better than that of the stand-alone mixed sensor. A NMR echo at 375 kHz shows a SNR only a factor 4 smaller than a tuned room temperature coil tightly wound around the sample, with a noise level which is a factor 3 better than for the volume coil. Our results suggest that mixed sensors are suitable for the integration of low-field MRI and MEG in a hybrid apparatus, where MEG and MRI would be recorded by SQUIDs and mixed sensors, respectively.

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SQUID-based instrumentation for ultralow-field MRI

Cited by 90 publications

References 25 publications

Parallel MRI at microtesla fields

Parallel MRI at microtesla fields

Postmortem analysis of a failed liquid nitrogen-cooled prepolarization coil for SQUID sensor-based ultra-low field magnetic resonance

NMR Detection at 8.9 Mt With a GMR Based Sensor Coupled to a Superconducting Nb Flux Transformer

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