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Natukunda F, Twongyirwe TM, Schiff SJ, Obungoloch J. Approaches in cooling of resistive coil-based low-field Magnetic Resonance Imaging (MRI) systems for application in low resource settings. BMC Biomed Eng 2021; 3:3. [PMID: 33579373 PMCID: PMC7881601 DOI: 10.1186/s42490-021-00048-6] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2020] [Accepted: 02/02/2021] [Indexed: 11/10/2022] Open
Abstract
Magnetic Resonance Imaging (MRI), a non-invasive method for the diagnosis of diverse health conditions has experienced growing popularity over other imaging modalities like ultrasound and Computer Tomography. Initially, proof-of-concept and earlier MRI systems were based on resistive and permanent magnet technology. However, superconducting magnets have long held monopoly of the market for MRI systems with their high-field (HF) strength capability, although they present high construction, installation, and siting requirements. Such stringent prerequisites restrict their availability and use in low-middle income countries. Resistive coil-based magnet, albeit low-field (LF) in capacity, represent a plausible boost for the availability and use of MRI systems in resource constrained settings. These systems are characterized by low costs coupled with substantial image quality for diagnosis of some conditions such as hydrocephalus common is such regions. However, the nature of resistive coils causes them to heat up during operation, thus necessitating a dedicated cooling system to improve image quality and enhance system longevity. This paper explores a range of cooling methods as have been applied to resistive magnets, citing their pros and cons and areas for improvement.
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Affiliation(s)
- Faith Natukunda
- Department of Biomedical Engineering, Mbarara University of Science and Technology, Mbarara, Uganda.
| | - Theodora M Twongyirwe
- Department of Mechanical Engineering, Mbarara University of Science and Technology, Mbarara, Uganda
| | - Steven J Schiff
- Centre for Neural Engineering, Departments of Engineering Science and Mechanics, Neurosurgery, and Physics, The Pennsylvania State University, Pennsylvania, USA
| | - Johnes Obungoloch
- Department of Biomedical Engineering, Mbarara University of Science and Technology, Mbarara, Uganda
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Flämig M, Hofmann M, Lichtinger A, Rössler EA. Application of proton field-cycling NMR relaxometry for studying translational diffusion in simple liquids and polymer melts. Magn Reson Chem 2019; 57:805-817. [PMID: 30604576 DOI: 10.1002/mrc.4823] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/29/2018] [Revised: 12/19/2018] [Accepted: 12/20/2018] [Indexed: 06/09/2023]
Abstract
With the availability of commercial field-cycling relaxometers together with progress of home-built instruments nuclear magnetic resonance relaxometry has gained new momentum as a method of investigating the dynamics in viscous liquids and polymer melts. The method provides the frequency dependence of the spin-lattice relaxation rate. In the case of protons, one distinguishes intramolecular and intermolecular relaxation pathways. Whereas the intramolecular contribution prevails at high frequencies and reflects rotational dynamics, the often ignored intermolecular relaxation contribution dominates at low-frequency and provides access to translational dynamics. A universal low-frequencies dispersion law holds which in pure systems allows determining the diffusion coefficient in a straightforward way. In addition, the rotational time constant is extracted from the high-frequency relaxation contribution. This is demonstrated for simple and ionic liquids and for polymer melts.
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Affiliation(s)
- Max Flämig
- Experimentalphysik and Nordbayerisches NMR-Zentrum, Universität Bayreuth, Bayreuth, Germany
| | - Marius Hofmann
- Experimentalphysik and Nordbayerisches NMR-Zentrum, Universität Bayreuth, Bayreuth, Germany
| | - Anne Lichtinger
- Experimentalphysik and Nordbayerisches NMR-Zentrum, Universität Bayreuth, Bayreuth, Germany
| | - Ernst A Rössler
- Experimentalphysik and Nordbayerisches NMR-Zentrum, Universität Bayreuth, Bayreuth, Germany
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Abstract
This paper describes an innovative solution for the power supply of a fast field cycling (FFC) nuclear magnetic resonance (NMR) spectrometer considering its low power consumption, portability and low cost. In FFC cores, the magnetic flux density must be controlled in order to perform magnetic flux density cycles with short transients, while maintaining the magnetic flux density levels with high accuracy and homogeneity. Typical solutions in the FFC NMR literature use current control to get the required magnetic flux density cycles, which correspond to an indirect magnetic flux density control. The main feature of this new relaxometer is the direct control of the magnetic flux density instead of the magnet current, in contrast with other equipment available in the market. This feature is a great progress because it improves the performance. With this solution it is possible to compensate magnetic field disturbances and parasitic magnetic fields guaranteeing, among other possibilities, a field control below the earth magnetic field. Experimental results validating the developed solution and illustrating the real operation of this type of equipment are shown.
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Ajoy A, Lv X, Druga E, Liu K, Safvati B, Morabe A, Fenton M, Nazaryan R, Patel S, Sjolander TF, Reimer JA, Sakellariou D, Meriles CA, Pines A. Wide dynamic range magnetic field cycler: Harnessing quantum control at low and high fields. Rev Sci Instrum 2019; 90:013112. [PMID: 30709175 DOI: 10.1063/1.5064685] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/07/2018] [Accepted: 01/06/2019] [Indexed: 06/09/2023]
Abstract
We describe the construction of a fast field cycling device capable of sweeping a 4-order-of-magnitude range of magnetic fields, from ∼1 mT to 7 T, in under 700 ms, and which is further extendable to a 1 nT-7 T range. Central to this system is a high-speed sample shuttling mechanism between a superconducting magnet and a magnetic shield, with the capability to access arbitrary fields in between with high resolution. Our instrument serves as a versatile platform to harness the inherent dichotomy of spin dynamics on offer at low and high fields-in particular, the low anisotropy, fast spin manipulation, and rapid entanglement growth at low field as well as the long spin lifetimes, spin specific control, and efficient inductive measurement possible at high fields. Exploiting these complementary capabilities in a single device opens up applications in a host of problems in quantum control, sensing, and information storage, besides in nuclear hyperpolarization, relaxometry, and imaging. In particular, in this paper, we focus on the ability of the device to enable low-field hyperpolarization of 13C nuclei in diamond via optically pumped electronic spins associated with nitrogen vacancy defect centers.
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Affiliation(s)
- A Ajoy
- Department of Chemistry, University of California, Berkeley, California 94720, USA
| | - X Lv
- Department of Chemistry, University of California, Berkeley, California 94720, USA
| | - E Druga
- Department of Chemistry, University of California, Berkeley, California 94720, USA
| | - K Liu
- Department of Chemistry, University of California, Berkeley, California 94720, USA
| | - B Safvati
- Department of Chemistry, University of California, Berkeley, California 94720, USA
| | - A Morabe
- Department of Chemistry, University of California, Berkeley, California 94720, USA
| | - M Fenton
- Department of Chemistry, University of California, Berkeley, California 94720, USA
| | - R Nazaryan
- Department of Chemistry, University of California, Berkeley, California 94720, USA
| | - S Patel
- Department of Chemistry, University of California, Berkeley, California 94720, USA
| | - T F Sjolander
- Department of Chemistry, University of California, Berkeley, California 94720, USA
| | - J A Reimer
- Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - D Sakellariou
- Centre for Surface Chemistry and Catalysis, Department of Microbial and Molecular Systems (M2S), KU Leuven, Celestijnenlaan 200F P.O. Box 2461, 3001 Leuven, Belgium
| | - C A Meriles
- Department of Physics, CUNY-City College of New York, New York, New York 10031, USA
| | - A Pines
- Department of Chemistry, University of California, Berkeley, California 94720, USA
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Affiliation(s)
- M. Flämig
- Experimentalphysik II, Universität Bayreuth, Bayreuth, Germany
| | - M. Hofmann
- Department of Chemistry, Louisiana State University, Baton Rouge, LA, USA
| | - E. A. Rössler
- Experimentalphysik II, Universität Bayreuth, Bayreuth, Germany
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Abstract
Controlled waveform magnets (CWMs) are a class of pulsed magnets whose pulse shape with time can be programmed by the user. With a CWM, the user gains control not only over the magnitude of the field but also over its rate of change. In this work we present a table-top CWM, driven by a capacitor bank, capable of producing virtually any user-shaped magnetic field waveform up to 10 tesla. Insulated gate bipolar transistor chips have been paralleled to form the high current switch and paralleled chips of SiC Schottky diodes form the crowbar diode module. Sample controlled waveforms including flat-tops up to 10 tesla and some triangular magnetic field pulses have been successfully generated for 10-20 ms with a ripple <1%.
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Redfield AG. High-resolution NMR field-cycling device for full-range relaxation and structural studies of biopolymers on a shared commercial instrument. J Biomol NMR 2012; 52:159-177. [PMID: 22200887 DOI: 10.1007/s10858-011-9594-1] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/11/2011] [Accepted: 12/05/2011] [Indexed: 05/31/2023]
Abstract
Improvements are described in a shuttling field-cycling device (Redfield in Magn Reson Chem 41:753-768, 2003), designed to allow widespread access to this useful technique by configuring it as a removable module to a commercial 500 MHz NMR instrument. The main improvements described here, leading to greater versatility, high reliability and simple construction, include: shuttling provided by a linear motor driven by an integrated-control servomotor; provision of automated bucking magnets to allow fast two-stage cycling to nearly zero field; and overall control by a microprocessor. A brief review of history and publications that have used the system is followed by a discussion of topics related to such a device including discussion of some future applications. A description of new aspects of the shuttling device follows. The minimum round trip time to 1T and above is less than 0.25 s and to 0.002 T is 0.36 s. Commercial probes are used and sensitivity is that of the host spectrometer reduced only by relaxation during travel. A key element is development of a linkage that prevents vibration of the linear motor from reaching the probe.
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Affiliation(s)
- Alfred G Redfield
- Biochemistry Department, Brandeis University, Mail stop 009, Waltham, MA 02154, USA.
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Sousa DM, Marques GD, Cascais JM, Sebastião PJ. Desktop fast-field cycling nuclear magnetic resonance relaxometer. Solid State Nucl Magn Reson 2010; 38:36-43. [PMID: 20688489 DOI: 10.1016/j.ssnmr.2010.07.001] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/08/2010] [Revised: 07/07/2010] [Accepted: 07/13/2010] [Indexed: 05/29/2023]
Abstract
In this paper a new type of Fast Field Cycling (FFC) Nuclear Magnetic Resonance (NMR) relaxometer with low power consumption (200W) and cycle to cycle field stability better than 10(-4) is described. The new high-permeability magnet was designed to allow for good magnetic field homogeneity and allows for the sample rotation around an axis perpendicular to magnetic field, operating with magnetic fields between 0 and 0.21T. The power supply of the new relaxometer was specially developed in order to have steady state accurate currents and allow for magnetic field switching times less than 3ms. Additional control circuits were developed and included to compensate the Earth magnetic field component parallel to the field axis and to compensate for parasitic currents. The main aspects of the developed circuits together with some calibrating experimental results using the liquid crystal compounds 5CB and 8CB are presented and discussed.
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Affiliation(s)
- Duarte Mesquita Sousa
- DEEC AC-Energia /CIEEE, Instituto Superior Técnico, TU Lisbon-Av. Rovisco Pais, 1049-001 Lisboa, Portugal.
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Van-Quynh A, Sebastião PJ, Wilson DA, Mehl GH. Detecting columnar deformations in a supermesogenic octapode by proton NMR relaxometry. Eur Phys J E Soft Matter 2010; 31:275-283. [PMID: 20300797 DOI: 10.1140/epje/i2010-10575-5] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/15/2009] [Revised: 01/18/2010] [Accepted: 02/01/2010] [Indexed: 05/29/2023]
Abstract
We used proton ( (1)H nuclear magnetic relaxation (NMR) dispersions to study the molecular dynamics in the isotropic phase and mesophases (nematic and columnar hexagonal) of a supermesogenic octapode formed by laterally connecting calamitic mesogens to an inorganic silsesquioxane cube through flexible spacers. The dispersions of the spin-lattice relaxation time (T(1)) are interpreted through relaxation mechanisms used for the study of molecular dynamics in low-molar-mass liquid crystals but adapted to the case of liquid crystalline supermolecules. At high frequencies (above 10MHz) the behaviour of the T(1) with the Larmor frequency is similar for all phases and is ascribed to local reorientations and/or rotations. At intermediate and low frequencies (below 10MHz) our results show notable differences in the T(1) behaviour with respect to the mesophases. The nematic (N) and isotropic (Iso) phases' low-frequency results are similar and are interpreted for both phases in terms of order director fluctuations (ODF), revealing that even in the isotropic phase local nematic order is detected by proton NMR relaxometry. Local nematic order in the Iso phase is interpreted in terms of the presence of nematic cybotactic clusters induced by the interdigitation of mesogens that is promoted by the silsesquioxane octapode molecular structure. In the columnar hexagonal (Col (h) phase, the T(1) dispersions show that elastic columnar deformations (ECD) dominate the nuclear magnetic relaxation below 10MHz. This result shows that the columnar packing of the octapode clearly restricts the collective fluctuations of the mesogenic units inspite of their local nematic order.
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Affiliation(s)
- A Van-Quynh
- Centro de Física da Matéria Condensada, Universidade de Lisboa, Av. Gama Pinto, 1649-003, Lisboa, Portugal.
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Filip D, Cruz C, Sebastião PJ, Cardoso M, Ribeiro AC, Vilfan M, Meyer T, Kouwer PHJ, Mehl GH. Phase structure and molecular dynamics of liquid-crystalline side-on organosiloxane tetrapodes. Phys Rev E Stat Nonlin Soft Matter Phys 2010; 81:011702. [PMID: 20365386 DOI: 10.1103/physreve.81.011702] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/07/2009] [Indexed: 05/29/2023]
Abstract
X-ray diffraction and proton NMR relaxation measurements were carried out on two liquid-crystalline organosiloxane tetrapodes with side-on mesogenic groups, exhibiting nematic and smectic- C phases, and on a monomeric analog. Packing models for the mesophases exhibited by these systems are proposed on the basis of x-ray diffraction data. As a consequence of microsegregation, the aromatic cores are packed in between two sublayers formed by a mixture of interdigitated aliphatic and siloxane chains. The mixed sublayers are characteristic for the tetrapodes with side-on mesogenic groups presented in this work and have not been observed in tetrapodes with terminally attached mesogens. The tilt angle in the smectic- C phase is found very large, i.e., approximately 61 degrees -62 degrees . Notably, smectic- C clusters are present also in the whole temperature range of the nematic phase. NMR relaxometry yields T(1)-1 dispersions clearly different from those of conventional calamitics. The influence of molecular tendency to form interdigitated structures is evidenced by frequency-dependent relaxation rate in the isotropic phase-indicating the presence of ordered clusters far above the phase transition-and by the diminished role of molecular self-diffusion in ordered phases. Nematiclike director fluctuations are the dominating relaxation mechanism whereas the translational displacements are strongly hindered by the interdigitation of dendrimer arms.
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Affiliation(s)
- D Filip
- Centro de Física da Matéria Condensada, Universidade de Lisboa, Lisboa, Portugal
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Filip D, Cruz C, Sebastião PJ, Ribeiro AC, Vilfan M, Meyer T, Kouwer PHJ, Mehl GH. Structure and molecular dynamics of the mesophases exhibited by an organosiloxane tetrapode with strong polar terminal groups. Phys Rev E Stat Nonlin Soft Matter Phys 2007; 75:011704. [PMID: 17358170 DOI: 10.1103/physreve.75.011704] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/27/2006] [Indexed: 05/14/2023]
Abstract
The polymorphism of a new organosiloxane tetrapode compound with cyano terminal polar groups was characterized by means of polarizing optical microscopy and x-ray diffraction. The compound exhibits smectic- A and smectic- C phases with a partial bilayer arrangement due to a certain degree of head-to-head association of the mesogenic units through their cyano end groups. On the basis of x-ray diffraction results, evidencing the microsegregation of polyphilic molecules, packing models for the smectic- A and smectic- C phases are proposed. A high degree of smectic positional order and a relatively low value of the tilt angle in the smectic- C phase are indicated. Molecular dynamics of the studied compound was investigated by means of proton NMR relaxometry. The frequency dispersions of the spin-lattice relaxation time (T1) show that the relaxation is induced by three rotational modes of individual dendrimer arms with frequencies between 10;{6} and 10;{9}Hz . In the smectic phases, the effect of individual rotations is overwhelmed by a well expressed contribution of layer undulations at Larmor frequencies below approximately 10MHz . The appearance of this relaxation mechanism over the frequency range of three decades is so far unique in the case of thermotropic liquid crystals. The analysis of the layer undulations contribution supports the microsegregation model of the smectic phases by revealing a slowing-down of translational diffusion and the lack of interactions among the sublayers formed by the mesogenic groups.
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Affiliation(s)
- D Filip
- Centro de Física da Matéria Condensada, Av. Prof. Gama Pinto 2, 1649-003 Lisbon, Portugal
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