Electricity: magnetically operated switches – magnets – and electr – Magnets and electromagnets – Magnet structure or material
Patent
1994-12-19
1997-08-19
Donovan, Lincoln
Electricity: magnetically operated switches, magnets, and electr
Magnets and electromagnets
Magnet structure or material
335216, 335299, 324318, H01F 100
Patent
active
056592817
DESCRIPTION:
BRIEF SUMMARY
This invention is in the field of electromagnets, and is more particularly directed to a shielded superconducting electromagnet for use in magnetic resonance imaging.
BACKGROUND OF THE INVENTION
High magnetic field electromagnets have become important elements in various types of equipment over recent years. One important type of such equipment is medical imaging equipment, such as the type commonly referred to as magnetic resonance imaging (MRI) equipment. This equipment utilizes the mechanism of nuclear magnetic resonance (NMR) to produce an image, and accordingly imaging systems operating according to this mechanism are also commonly referred to as NMR imaging systems.
As is well known in the field of MRI, a high DC magnetic field is generated to polarize the gyromagnetic atomic nuclei of interest (i.e., those atomic nuclei that have nonzero angular momentum, or nonzero magnetic moment) contained within the volume to be imaged in the subject. The magnitude of this DC magnetic field currently ranges from on the order of 0.15 Tesla to 2.0 Tesla; it is contemplated that larger fields, ranging as high as 4.0 to 6.0 Tesla, may be useful in the future, particularly to perform spectroscopy as well as tomography. The volume of the subject to be imaged (i.e., the volume of interest, or "VOI") is that volume which receives the high DC magnetic field, and within which the DC field is substantially uniform.
Imaging is accomplished in the VOI utilizing the mechanism of nuclear magnetic resonance in the gyromagnetic atomic nuclei contained therewithin. As such, in addition to the large field DC magnet, the MRI apparatus includes an oscillator coil to generate an oscillating magnetic field oriented at an angle relative to the DC field, and at a frequency matching the resonant frequency of the atoms of interest in the selected volume; frequencies of interest in modern MRI are in the radio frequency (RF) range. As the gyromagnetic nuclei in the defined volume will have a common resonant frequency different from atoms outside of the volume, modulation of a gradient magnetic field (produced by a gradient coil) allows sequential imaging of small volumes. The images from the small volumes are then used to form a composite image of the larger volume, such as the internal organ or region of interest. To produce the series of images, the MRI apparatus also includes a detecting coil in which a current can be induced by the nuclear magnetic dipoles in the volume being imaged.
In operation, as is well known, the magnetic dipole moments of those atoms in the volume which are both gyromagnetic and also resonant at the frequency of the oscillating field are rotated from their polarized orientation by the resonant RF oscillation by a known angle, for example 90.degree.. The RF excitation is then removed, and the induced current in the detecting coil is measured over time to determine a decay rate, which corresponds to the quantity of the atoms of interest in the volume being imaged. Incremental sequencing of the imaging process through the selected volume by modulations in the gradient field can provide a series of images of the subject that correspond to the composition of the subject. Conventional MRI has been successful in the imaging of soft tissues, such as internal organs and the like, which are transparent to X-rays.
It is well known in the art that the spatial resolution of MRI tomography improves as the strength of the available magnetic field increases. Conventional MRI equipment useful in diagnostic medical imaging requires high DC magnetic fields, such as 5 kgauss or greater.
Due to the large number of ampere-turns necessary to produce such high magnetic fields, conventional MRI systems now generally utilize superconducting wire in their DC coils. While the magnitude of the current carried in these coils is extremely high, the superconducting material and accompanying cryogenic systems required in such magnets are quite expensive, and also add significantly to the size and weight of the magnet in the MRI apparatus. In
REFERENCES:
patent: 4490675 (1984-12-01), Knuettell et al.
patent: 4587490 (1986-05-01), Muller et al.
patent: 4589591 (1986-05-01), McDougall
patent: 4590428 (1986-05-01), Muller et al.
patent: 4590452 (1986-05-01), Ries et al.
patent: 4595899 (1986-06-01), Smith et al.
patent: 4612505 (1986-09-01), Zijlstra
patent: 4646045 (1987-02-01), Chari et al.
patent: 4689591 (1987-08-01), McDougall
patent: 4701736 (1987-10-01), McDougall et al.
patent: 4721914 (1988-01-01), Fukushima et al.
patent: 4724412 (1988-02-01), Kalafala
patent: 4783628 (1988-11-01), Huson
patent: 4822772 (1989-04-01), Huson
patent: 4912445 (1990-03-01), Yomasaki et al.
patent: 4924185 (1990-05-01), Matsutani
patent: 4968915 (1990-11-01), Wilson et al.
patent: 4987398 (1991-01-01), Bessho
patent: 5001448 (1991-03-01), Srivastava et al.
patent: 5003979 (1991-04-01), Merickel et al.
patent: 5006804 (1991-04-01), Dorri et al.
patent: 5012217 (1991-04-01), Palkovich et al.
patent: 5049848 (1991-09-01), Pulyer
patent: 5117188 (1992-05-01), Ohkawa
patent: 5359310 (1994-10-01), Pissanetzky
patent: 5382904 (1995-01-01), Pissanetzky
patent: 5519372 (1996-05-01), Palkovich et al.
Siebold, et al., "Performance and Results of a Computer Program for Optimizing Magnets with iron," IEEE Trans. Magnetics, vol. 24, No. 1 (IEEE, Jan. 1988), pp. 419-422.
Everett, et al. "Spherical coils for uniform magnetic fields," J. Sci. Instrum., vol. 43 (1966), pp. 470-474.
M.W. Garrett, "Thick Cylindrical Coil Systems for Strong Magnetic Field or Gradient Homogeneities of the 6th to 20th Order," J. Appl. Phys. vol. 38 No. 6, (1967) pp. 2578-2583.
Pissanetzky, "Minimum energy MRI gradient coils of general geometry," Meas. Sci. Technol., vol. 3 (IOP Publishing Ltd., 1992) pp. 667-673.
Pissanetzky, "Structured coils for NMR applications" IEEE Trans. Magnetics, vol. 28, No. 4 (IEEE Jul. 1992), pp. 1961-1968.
Pissanetzky, "Structured Coils and Nonlinear Iron", presented at the 5th Biennial IEEE Conference on Electromagnet Field Computation, Claremont, Calif. (Aug. 3-5, 1992).
McIntyre Peter M.
Pissanetzky Sergio
Donovan Lincoln
Houston Advanced Research Center
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