Publications
26 results found
Lanz H, Ristic M, Chappell K, et al., 2023, Minimum number of scans for collagen fibre direction estimation using Magic Angle Directional Imaging (MADI) with a priori information, Array, Vol: 17, Pages: 1-10, ISSN: 2590-0056
Tissues such as tendons, ligaments, articular cartilage, and menisci contain significant amounts of organised collagen which gives rise to the Magic Angle effect during magnetic resonance imaging (MRI). The MR intensity response of these tissues is dependent on the angle between the main field, B0, and the direction of the collagen fibres. Our previous work showed that by acquiring scans at as few as 7–9 different field orientations, depending on signal to noise ratio (SNR), the tissue microstructure can be deduced from the intensity variations across the set of scans. Previously our Magic Angle Directional Imaging (MADI) technique used rigid registration and manual final alignment, and did not assume any knowledge of the target anatomy being scanned. In the present work, fully automatic soft registration is incorporated into the MADI workflow and a priori knowledge of the target anatomy is used to reduce the required number of scans. Simulation studies were performed to assess how many scans are theoretically necessary. These findings were then applied to MRI data from a caprine knee specimen. Simulations suggested that using 3 scans might be sufficient, but in practice 4 scans were necessary to achieve high accuracy. 5 scans only offered marginal gains over 4 scans. A 15 scan dataset was used as a gold standard for quantitative voxel-to-voxel comparison of computed fibre directions, qualitative comparison of collagen tractography plots are also presented. The results are also encouraging at low SNR values, showing robustness of the method and applicability at low field.
McGinley JVM, Ristic M, Young IR, 2016, A permanent MRI magnet for magic angle imaging having its field parallel to the poles, Journal of Magnetic Resonance, Vol: 271, Pages: 60-67, ISSN: 1090-7807
A novel design of open permanent magnet is presented, in which the magnetic field is oriented parallel to the planes of its poles. The paper describes the methods whereby such a magnet can be designed with a field homogeneity suitable for Magnetic Resonance Imaging (MRI). Its primary purpose is to take advantage of the Magic Angle effect in MRI of human extremities, particularly the knee joint, by being capable of rotating the direction of the main magnetic field B0 about two orthogonal axes around a stationary subject and achieve all possible angulations. The magnet comprises a parallel pair of identical profiled arrays of permanent magnets backed by a flat steel yoke such that access in lateral directions is practical. The paper describes the detailed optimization procedure from a target 150 mm DSV to the achievement of a measured uniform field over a 130 mm DSV. Actual performance data of the manufactured magnet, including shimming and a sample image, is presented. The overall magnet system mounting mechanism is presented, including two orthogonal axes of rotation of the magnet about its isocentre.
McGinley JVM, Young IR, 2015, Electromagnet Assembly, US 8947090
An electromagnet assembly comprises a first pair of substantially co-planar coils wound in opposite senses to each other. It further comprises a second pair of co-planar coils also wound in opposite senses to each other. The coil pairs are arranged substantially parallel to, and spaced apart from, each other. In use, the field shape and direction produced by the first coil pair are substantially mirrored by those produced by the second coil pair.
Ristic M, Gryska Y, McGinley JVM, et al., 2013, Supercapacitor Energy Storage for Magnetic Resonance Imaging Systems, IEEE Transactions on Industrial Electronics, Vol: PP, ISSN: 0278-0046
Magnetic Resonance Imaging (MRI) involves very short pulses of very high current. Substantial savings in the high cost of MRI installations may be realised by employing suitable electrical energy storage, for which supercapacitors are strong candidates in view of high specific power and long cycle life. A key question is whether the well-known capacitance degradation with increased frequency is compatible with the complex and highly variable duty cycles of various MRI sequences. Compatibility of the supercapacitor voltage range with the MRI system must also be considered. We present a detailed analysis of power duty profiles in MRI, using actual imaging sequences, that has not been reported previously. We also propose and validate a simplified supercapacitor model that can accurately simulate its performance in the MRI system, involving pulses several orders of magnitude shorter than those considered previously. Results of equivalent experiments involving Lithium-Ion Iron Phosphate (LiFePO4) batteries are also reported. Finally, we present a detailed analysis of the overall energy storage performance in a realistic neurological examination. The study is based on a specific system of our own design and we fully disclose its relevant parameters, so that the results would be of direct practical value to the wider community, including developers of MRI.
Awan SA, Mcginley JVM, Dickinson RJ, et al., 2012, Design and development of a planar B0-coil for patient respiratory motion correction in magnetic resonance imaging, CONCEPTS IN MAGNETIC RESONANCE PART B-MAGNETIC RESONANCE ENGINEERING, Vol: 41B, Pages: 130-138, ISSN: 1552-5031
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Ristic M, McGinley JVM, Lorenzoni F, 2011, Numerical Study of Quench Protection Schemes for a MgB<sub>2</sub> Superconducting Magnet, IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, Vol: 21, Pages: 3501-3508, ISSN: 1051-8223
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McGinley JVM, DeMeester GD, Morich MA, et al., 2004, Method and apparatus for aligning a magnetic field modifying structure in a magnetic resonance imaging scanner, US 6836119
In a method for aligning a magnetic field-modifying structure (74) in a magnet bore (12) of a magnetic resonance imaging scanner (8), a reference magnetic field map of the magnet bore (12) is measured without the magnetic field-modifying structure (74) inserted. The magnetic field-modifying structure (74) is inserted into the magnet bore (12). A second magnetic field map of the magnetic bore (12) is measured with the magnetic field-modifying structure (74) inserted. At least one odd harmonic component of the first and second magnetic field maps is extracted. The magnetic field-modifying structure (74) is aligned in the magnet bore (12) based on a comparison of the odd harmonic component of the first and second magnetic field maps.
McGinley JVM, Young IR, DeMeester GD, et al., 2001, MRI magnet with high homogeneity, patient access, and low forces on the driver coils, US 6218838
A pair of annular magnets (10) generate a vertical magnetic flux field through an imaging volume (12). The flux is focused by a pair of Rose rings (26) of high cobalt steel. A high order shim set includes a plurality of permanently magnetized or magnetized iron rings (32a, 32b, 32c, 32d) which cooperatively interact with the magnet assembly to optimize the homogeneity of the magnetic flux through the imaging volume. One of the permanent magnetic rings (32d), is mounted with an opposite polarity relative to the others. The magnetized rings are mounted in a non-ferrous, electrically insulating support structure (34) such that gradient coils (50) can be positioned behind the permanent magnet rings. A flux return path (14, 16, 18, 20, 22, 24) provides a low flux resistant path from adjacent the Rose ring at one side of the imaging volume remotely around the imaging volume to a position adjacent the Rose ring at the other side of the imaging volume.
McGinley JVM, Young IR, DeMeester GD, 2001, Magnetic resonance operating room magnet, US 6208144
A region of interest of a subject (20) on a subject support (18) is positioned above a ferrous pedestal (16, 116) that is supported on a ferrous floor yoke portion (76, 176). A lower imaging coil assembly (50) including a lower gradient coil (52), a radio frequency coil (54), and a lower pole piece (58) are disposed between the pedestal and a region of interest of the subject. An upper imaging coil assembly (40) including an annular gradient coil (42, 142) and an upper annular pole piece (44, 144) is supported from a ceiling ferrous yoke member (74, 174). The upper imaging coil assembly is supported by supports (70, 170) which are moved by drives (72, 78, 172) to raise and lower the upper imaging coil assembly. A laser gauging system (80, 180) gauges the position of the upper imaging coil assembly such that, with a control circuit (82), the upper imaging coil assembly is accurately repositioned at preselected imaging positions. A main magnetic field coil (30, 130) is positioned adjacent one of the ceiling ferrous yoke member and the floor ferrous yoke member to provide an asymmetric source of magnetic flux. Pre-polarizing coils (60, 62) are supported on the upper and lower imaging coil assemblies for boosting the magnetic field strength through the region of interest immediately preceding imaging sequences.
Paley M, Mayhew JE, Martindale AJ, et al., 2001, Design and initial evaluation of a low-cost 3-Tesla research system for combined optical and functional MR imaging with interventional capability, Journal of Magnetic Resonance Imaging, Vol: 13, Pages: 87-92, ISSN: 1053-1807
A 3-Tesla research system has been developed for functional and interventional magnetic resonance imaging (MRI) procedures on animal models based on a low field niche spectrometer. Use of two stages of fourth harmonic frequency multiplication has allowed us to produce a high-frequency spectrometer with good frequency stability based on a low-frequency direct digital synthesizer. The system has been designed with the ability to introduce interventional tools such as biopsy needles, radiofrequency (RF) electrodes, and fiber optics for optical spectroscopy and thermal ablation as well as drug infusions to allow function to be studied in the presence of external challenges. Full MR-compatible physiologic support capability allows animals to be maintained in a stable condition over extended periods of study. Functional MR images have been acquired by using gradient echoes (TR/TE = 40/12 msec) from the rat whisker barrel cortex using electrical stimulation (5-V, 1.5-mA, 1-msec pulses at 5 Hz via two needle electrodes inserted into the rat whisker pad). Initial results using respiratory gas challenges of 100% N2, 100% O2, and 10% CO2 have shown excellent agreement between single wavelength (633 nm) optical and functional MR time series with sub-second time resolution. The 1-mm copper electrodes for interventional radiofrequency ablation procedures were easily visualized in the superior colliculus by using gradient echo sequences. This novel, low-cost, high field system appears to be a useful research tool for functional and interventional studies of rat brain and allows concurrent optical spectroscopy. © 2001 Wiley-Liss, Inc.
Paley M, Mayhew JE, Martindale AJ, et al., 2001, Design and initial evaluation of a low-cost 3-Tesla research system for combined optical and functional MR imaging with interventional capability., J Magn Reson Imaging, Vol: 13, Pages: 87-92, ISSN: 1053-1807
A 3-Tesla research system has been developed for functional and interventional magnetic resonance imaging (MRI) procedures on animal models based on a low field niche spectrometer. Use of two stages of fourth harmonic frequency multiplication has allowed us to produce a high-frequency spectrometer with good frequency stability based on a low-frequency direct digital synthesizer. The system has been designed with the ability to introduce interventional tools such as biopsy needles, radiofrequency (RF) electrodes, and fiber optics for optical spectroscopy and thermal ablation as well as drug infusions to allow function to be studied in the presence of external challenges. Full MR-compatible physiologic support capability allows animals to be maintained in a stable condition over extended periods of study. Functional MR images have been acquired by using gradient echoes (TR/TE = 40/12 msec) from the rat whisker barrel cortex using electrical stimulation (5-V, 1.5-mA, 1-msec pulses at 5 Hz via two needle electrodes inserted into the rat whisker pad). Initial results using respiratory gas challenges of 100% N(2), 100% O(2), and 10% CO(2) have shown excellent agreement between single wavelength (633 nm) optical and functional MR time series with subsecond time resolution. The 1-mm copper electrodes for interventional radiofrequency ablation procedures were easily visualized in the superior colliculus by using gradient echo sequences. This novel, low-cost, high field system appears to be a useful research tool for functional and interventional studies of rat brain and allows concurrent optical spectroscopy. J. Magn. Reson. Imaging 2001;13:87-92.
Paley M, Mayhew JE, Martindale AJ, et al., 2001, Design and initial evaluation of a low‐cost 3‐Tesla research system for combined optical and functional MR imaging with interventional capability, Journal of Magnetic Resonance Imaging, Vol: 13, Pages: 87-92, ISSN: 1053-1807
McGinley JVM, DeMeester GD, Young IR, 2000, Magnetic resonance imaging with integrated poleface features, US 6147495
A magnetic resonance imaging scanner includes a pair of opposing pole pieces (20, 20') disposed symmetrically about an imaging volume (24) facing one another. The pair of opposing pole pieces (20, 20') includes a first ferrous pole piece (20) which has a front side (22) facing the imaging volume (24) and a back side (28). Also included is a second ferrous pole piece (20') which also has a front side (22) facing the imaging volume (24) and a back side (28). A magnetic flux return path (30) extends, remotely from the imaging volume (24), between a point adjacent the back side 28 of the first pole piece (20) and a point adjacent the back side 28' of the second pole piece (20)'. A source of magnetic flux generates a magnetic flux through the imaging volume (24), the pair of opposing pole pieces (20, 20'), and the magnetic flux return path (30). An array of annular hoops (40) and (40') are integrated with the pair of opposing pole pieces (20, 20') for homogenizing the magnetic flux through the imaging volume (24). The annular hoops (40, 40') are made of a material having magnetic properties different from those of the pair of opposing pole pieces (20, 20').
McGinley JVM, DeMeester GD, Srivastava VC, 1997, High order passive shimming assembly for MRI magnets, US 5635839
McGinley JVM, Srivastava VC, DeMeester GD, 1997, 5532597 Passive shimming technique for MRI magnets, Magnetic Resonance Imaging, Vol: 15, Pages: XIX-XIX, ISSN: 0730-725X
McGinley JVM, Srivastava VC, DeMeester GD, 1996, Passive shimming technique for MRI magnets, US 5532597
A subject receiving bore (12) of a magnetic resonance apparatus has an axial length to diameter ratio of less than 1.75:1 and preferably about 2:1. The temporally constant magnetic field generated by superconducting magnets (10) surrounding the bore have various magnetic field harmonic distortions generally in the Z1-Z18 range. Shim trays (80) are disposed longitudinally around the bore (12). Each shim tray contains a number of shim pockets (84) which receive ferrous shims for shimming the magnetic field in the bore (12). An initialization system (60) calibrates the initial magnetic field within the bore (12). An initial shim distribution is determined which shims the inhomogeneous magnetic field toward a target more homogeneous magnetic field. An optimization system (66) determines a residual magnetic field from a difference between the present inhomogeneous magnetic field of the bore and the target magnetic field. The amounts of ferrous material assigned to each shim pocket are optimized in fractional groups to determine an optimal shim settings to produce a shimming magnetic field equal to a negative of the residual magnetic field. In this manner, the net magnetic field is substantially equal to the target homogeneous magnetic field.
McGinley JVM, Paley MNJ, 1994, Apparatus for Magnetic Resonance Measurement, WO 9510786
Apparatus for magnetic resonance imaging which includes a magnet (2) having a yoke (8) which is smoothly curved to prevent flux loss, as well as to reduce the size of the magnet whilst retaining the useful volume. The apparatus also includes providing a single enclosure (30) for the imaging device and shielded vehicles (50, 70) for enclosing patients during imaging.
McGinley JVM, 1990, 4870380 Magnet arrangements, Magnetic Resonance Imaging, Vol: 8, Pages: III-IV, ISSN: 0730-725X
McGinley JVM, 1989, Magnet Arrangements, US 4870380
A magnet arrangement for producing a magnet field in a gap (3) between a pair of pole pieces (1), e.g. to provide the main magnetic field for application to a subject for magnetic resonance imaging, wherein adjacent the pole pieces the magnet core 15 has sections 17 of restricted cross-sectional area which serve to improve the homogeneity of the field in the gap.
McGinley JVM, 1988, 4710741 Electromagnet arrangements for producing a magnetic field of high homogenity, Magnetic Resonance Imaging, Vol: 6, Pages: IV-IV, ISSN: 0730-725X
McGinley JVM, 1987, Electromagnet arrangements for producing a magnetic field of high homogenity, US 4710741
A coil arrangement for producing a magnetic field of high homogeneity, such as is required in magnetic resonance imaging, comprising a single pair of identical annular coils (17A, 17B) disposed coaxially in spaced relationship and a pair of annular members (19A, 19B) of ferromagnetic material disposed coaxially with the coils, symmetrically with respect to the plane which perpendicularly intersects the axis of the coils centrally between them. The coils and ferromagnetic members have dimensions and are relatively positioned so that, with the coils carrying equal energizing currents, the more significant spherical harmonic coefficients are eliminated.
Corney A, McGinley JVM, 1982, Collisional effects and two-photon absorption in calcium vapour, Journal of Physics B: Atomic and Molecular Physics, Vol: 15, Pages: L655-L660, ISSN: 0022-3700
Corney A, McGinley JVM, 1981, Tunable dye laser spectroscopy of atomic calcium: collisional redistribution of radiation, Journal of Physics B: Atomic and Molecular Physics, Vol: 14, Pages: 3047-3067, ISSN: 0022-3700
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