Magnetic Resonance Imaging System Based on Earth's Magnetic Field

Mohorič, Aleš; Planinšič, Gorazd; Kos, Miha; Duh, Andrej; Stepišnik, Janez

doi:10.1081/ci-200037034

Cited by 40 publications

(26 citation statements)

References 32 publications

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“…SQUIDs with untuned input circuits are typically employed [16][17][18][19][20][21][22][23][24][25][26][27], because their response is independent of frequency. Low-field images acquired using tuned SQUID pre-amplifiers [33], as well as Faraday detector coils [36,37], have also been reported, though the method of [16][17][18][19][20][21][22][23][24][25][26][27] appears to be more efficient. Despite these improvements, insufficiently high SNR remains a major limitation in presentday ULF MRI.…”

Section: Introductionmentioning

confidence: 99%

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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Section: Introductionmentioning

confidence: 99%

Parallel MRI at microtesla fields

Zotev

Volegov

Matlashov

et al. 2008

Journal of Magnetic Resonance

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“…The authors were able to generate images of water-filled tubes and of various fruits, with a slice thickness of ∼ 1 cm and in-plane resolution of ∼ 2 mm. More recently, the same group has published details of an improved Earth's field imaging system, this time using pre-polarisation at 60 mT [12]. Other workers have taken a similar approach, using pre-polarisation prior to signal detection in the Earth's field [13] or even at zero field [14].…”

Section: Earth's Magnetic Field Fc-mrimentioning

confidence: 93%

Fast field-cycling magnetic resonance imaging

Lurie

Aime

Baroni

et al. 2010

Comptes Rendus. Physique

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Fast-field cycling magnetic resonance imaging FFC-MRI Earth-field MRI Pre-polarised MRI Free-radical imaging Magnetisation-transfer contrast Mots-clés : IRM en champ cyclé FFC-IRM IRM en champ magnétique terrestre IRM prépolarisée Imagerie par radicaux libres Contraste par transfert de magnetisationMagnetic resonance imaging (MRI) and fast field-cycling (FFC) NMR are both welldeveloped methods. The combination of these techniques, namely fast field-cycling magnetic resonance imaging (FFC-MRI) is much less well-known. Nevertheless, FFC-MRI has a number of significant applications and advantages over conventional techniques, and is being pursued in a number of laboratories. This article reviews the progress in FFC-MRI over the last two decades, particularly in the areas of Earth's field and prepolarised MRI, as well as free radical imaging using field-cycling Overhauser MRI. Different approaches to magnet design for FFC-MRI are also described. The paper then goes on to discuss recent techniques and applications of FFC-MRI, including protein measurement via quadrupolar cross-relaxation, contrast agent studies, localised relaxometry and FFC-MRI with magnetisation-transfer contrast. r é s u m é L'imagerie par Résonance Magnétique (IRM, ou MRI en anglais) et la RMN avec cyclage de champ rapide (« fast field cycling », FFC) sont toutes deux des méthodes bien développées. La combinaison de ces techniques, c'est-à-dire l'imagerie par résonance magnétique avec cyclage de champ rapide (FFC-MRI en anglais) est beaucoup moins bien connue. Cependant, la FFC-MRI a un nombre d'applications et d'avantages significatifs par rapport aux techniques conventionnelles, et son étude est poursuivie dans un certain nombre de laboratoires. Cet article passe en revue les progrès de la FFC-MRI au cours des deux dernières décennies, en particulier dans les domaines de l'imagerie en champ terrestre avec pré-polarisation, de même que l'imagerie des radicaux libres en utilisant la FFC-MRI avec effet Overhauser. Diverses approches à la conception des aimants pour FFC-MRI sont également décrites. L'article continue en discutant des techniques et applications récentes de la FFC-MRI, telles que la mesure des protéines par relaxation croisée quadrupolaire, les études d'agents de contraste, la relaxométrie localisée et la FFC-MRI avec contraste par transfert d'aimantation.

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“…The use of a high-Q receive coil in this instance would result in the frequency-encoded signal outside of the narrow coil response function being attenuated significantly [43,47], possibly to the extent of being unrecoverable via post processing. Thus, we have employed low-Q coils with a high filling factor design to mitigate the issue of finite coil bandwidth at low frequencies [60][61][62]. Lowering the coil Q results in a slight, but inevitable trade-off in image SNR [60,62], however the large signal obtained from hyperpolarized samples allows this to be tolerated to some degree.…”

Section: Hardware Performancementioning

confidence: 99%

“…Thus, we have employed low-Q coils with a high filling factor design to mitigate the issue of finite coil bandwidth at low frequencies [60][61][62]. Lowering the coil Q results in a slight, but inevitable trade-off in image SNR [60,62], however the large signal obtained from hyperpolarized samples allows this to be tolerated to some degree. As a result, we have obtained images (Figure 10) with high SNR that do not suffer variable attenuation across the image frequency range due to a convolution of the coil response on the image data, nor non-uniform noise floors (as were observed previously and which required considerable post-processing in order to partly correct the effect [43]).…”

Section: Hardware Performancementioning

confidence: 99%

An open-access, very-low-field MRI system for posture-dependent 3He human lung imaging

Tsai

Mair

Rosen

et al. 2008

Journal of Magnetic Resonance

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We describe the design and operation of an open-access, very-low-field, magnetic resonance imaging (MRI) system for in-vivo hyperpolarized 3 He imaging of the human lungs. This system permits the study of lung function in both horizontal and upright postures, a capability with important implications in pulmonary physiology and clinical medicine, including asthma and obesity. The imager uses a bi-planar B 0 coil design that produces an optimized 65 G (6.5 mT) magnetic field for 3 He MRI at 210 kHz. Three sets of bi-planar coils produce the x, y, and z magnetic field gradients while providing a 79-cm inter-coil gap for the imaging subject. We use solenoidal Q-spoiled RF coils for operation at low frequencies, and are able to exploit insignificant sample loading to allow for pretuning/matching schemes and for accurate pre-calibration of flip angles. We obtain sufficient SNR to acquire 2D 3 He images with up to 2.8 mm resolution, and present initial 2D and 3D 3 He images of human lungs in both supine and upright orientations. 1 H MRI can also be performed for diagnostic and calibration reasons.

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Magnetic Resonance Imaging System Based on Earth's Magnetic Field

Cited by 40 publications

References 32 publications

Parallel MRI at microtesla fields

Parallel MRI at microtesla fields

Fast field-cycling magnetic resonance imaging

An open-access, very-low-field MRI system for posture-dependent 3He human lung imaging

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