초록 ▼

To reduce vibration and noise generated in supplying pulsatile current to the gradient magnetic field coil for driving that coil in a MRI apparatus, an active shielded gradient magnetic field coil is used, in which the gradient magnetic field coil is supported by and fixed to the static magnetic fie

To reduce vibration and noise generated in supplying pulsatile current to the gradient magnetic field coil for driving that coil in a MRI apparatus, an active shielded gradient magnetic field coil is used, in which the gradient magnetic field coil is supported by and fixed to the static magnetic field generating magnet. The supporter for supporting this gradient magnetic field coil in non-contact does not prevent the interventional procedure performed by a doctor. Further, an eddy current generated on the surface of the static magnetic field generating magnet near the periphery of the gradient magnetic field coil, when supplying the pulsatile current to the gradient magnetic field coil, can be reduced.

대표청구항 ▼

1. A magnetic resonance imaging apparatus comprising:a pair of static magnetic field generating means; a yoke unit for supporting said pair of static magnetic field generating means; a pair of gradient magnetic field generating means for applying a magnetic field strength gradient to a static magnet

1. A magnetic resonance imaging apparatus comprising:a pair of static magnetic field generating means; a yoke unit for supporting said pair of static magnetic field generating means; a pair of gradient magnetic field generating means for applying a magnetic field strength gradient to a static magnetic field generated by said static magnetic field generating means; and supporting means for supporting said pair of gradient magnetic field generating means, which supporting means fix said pair of gradient magnetic field generating means to said yoke unit so as not to touch said static magnetic field generating means, wherein said static magnetic field generating means has an open hole space penetrating through said static magnetic field generating means in the same direction as the direction of the magnetic field generated by said static magnetic field generating means, and said gradient magnetic field generating means is fixed to said yoke unit through a support structure body including a supporting member arranged to pass through said open hole space. 2. A magnetic resonance imaging apparatus according to claim 1, wherein said gradient magnetic field generating means is fixed at its periphery to a supporting member surrounding said static magnetic field generating means.3. A magnetic resonance imaging apparatus according to claim 1, wherein vibration damping material is placed between the periphery of said gradient magnetic field generating means and said static magnetic field generating means.4. A magnetic resonance imaging apparatus according to claim 1, wherein said gradient magnetic field generating means is covered with a sound absorption mat.5. A magnetic resonance imaging apparatus according to claim 4, wherein said second supporting member is fixed on a floor and/or a ceiling.6. A magnetic resonance imaging apparatus according to claim 1, wherein said gradient magnetic field generating means is comprised of a first nonmagnetic supporting member arranged in the open hole space of said static magnetic field generating means and a second nonmagnetic supporting member arranged at the rear of said static magnetic field generating means.7. A magnetic resonance imaging apparatus according to claim 1, wherein the supporting member arranged in the open hole space of said static magnetic field generating means is in the form of a hollow bar.8. A magnetic resonance imaging apparatus according to claim 7, wherein a cable for supplying current to said gradient magnetic field generating means or a cooling pipe for sending to said gradient magnetic field generating means refrigerant for absorbing heat generated at said gradient magnetic field generating means is inserted in the open hole space of said supporting member.9. A magnetic resonance imaging apparatus according to claim 1, wherein the yoke unit is at least partially made of ferromagnetic material.10. A magnetic resonance imaging apparatus according to claim 1, wherein the supporting means is at least partially made of ferromagnetic material.11. A magnetic resonance imaging apparatus comprising:a pair of static magnetic field generating means; a yoke unit for supporting said pair of static magnetic field generating means; a pair of gradient magnetic field generating means for applying magnetic field strength gradient to a static magnetic field generated by said static magnetic field generating means; and supporting means for supporting said pair of gradient magnetic field generating means, such that there is no solid propagation of vibration, generated by said pair of gradient magnetic field generating means when they are driven directly, to said static magnetic field generating means. 12. A magnetic resonance imaging apparatus according to claims 11, wherein the plane of the gradient magnetic field generating means is perpendicular to the direction of the static magnetic field.13. A magnetic resonance imaging apparatus according to claim 11, wherein the yoke unit has an energy-absorbing mass to absorb vibrational-energy generated by the pair of gradient magnetic field generating means, such that there is no solid propagation of vibration to said static magnetic field generating means.14. A magnetic resonance imaging apparatus according to claim 11, wherein vibration damping material is placed between a periphery of said gradient magnetic field generating means and said static magnetic field generating means.15. A magnetic resonance imaging apparatus according to claim 11, wherein said gradient magnetic field generating means is covered with a sound absorption mat.16. A magnetic resonance imaging apparatus comprising:a pair of static magnetic field generating means; a yoke unit for supporting said pair of static magnetic field generating means; a pair of gradient magnetic field generating means for applying a magnetic field strength gradient to a static magnetic field generated by said static magnetic field generating means; and supporting means for supporting said pair of gradient magnetic field generating means, which supporting means fix said pair of gradient magnetic field generating means to said yoke unit so as not to touch said static magnetic field generating means. 17. A magnetic resonance imaging apparatus according to claim 16, wherein said gradient magnetic field generating means is fixed to said yoke unit through a supporting member surrounding said static magnetic field generating means.18. A magnetic resonance imaging apparatus according to claim 16, wherein the plane of the gradient magnetic field generating means is perpendicular to the direction of the static magnetic field.19. A magnetic resonance imaging apparatus according to claim 16, wherein the yoke unit is at least partially made of ferromagnetic material.20. A magnetic resonance imaging apparatus according to claim 16, wherein the supporting means is at least partially made of ferromagnetic material.21. A gradient magnetic field coil comprising:a main coil for generating a gradient magnetic field, which consists of a gradient magnetic field coil arranged on a flat plane for use in an MRI apparatus; a first shield coil arranged at the rear of said main coil, for generating a magnetic field for canceling the magnetic field generated at the rear of said main coil; and a second shield coil for generating a magnetic field to be combined with the magnetic field generated by said first shield coil, for canceling the magnetic field generated by said main coil, wherein the second shield coil takes up a circular region with a diameter greater than the maximum diameter of said main coil. 22. A gradient magnetic field coil comprising;a main coil for generating a gradient magnetic field on its front side, an electric conductor of which is spirally wound on an almost flat surface; a first shield coil for canceling at least partially the magnetic field generated by said main coil at the rear of said main coil, comprising an electric conductor spirally wound on an almost plain surface; and a second shield coil arranged parallel to the surface on which said main coil is arranged and the surface on which said shield coil is arranged to generate a magnetic field of such strength distribution that when combined with that of said first shield coil, it cancels the magnetic field at the outer edge of said gradient magnetic field coil. 23. A gradient magnetic field coil according to claim 22, wherein said second shield coil has a coil conductor that is connected to a coil conductor on the periphery of said first shield coil, and current in the same direction as that in the coil conductor of said first shield coil is applied to said second shield coil conductor.24. A gradient, magnetic field coil according to claim 22, wherein the surface on which said second shield coil is arranged is set between the surface on which said main coil is arranged and that on which said first shield coil is arranged.25. A gradient magnetic field coil according to claim 22, wherein the surface on which the second shield coil is arranged is identical with the surface on which the first shield coil is arranged.26. A gradient magnetic field coil comprising:a main coil for generating a gradient magnetic field on its front side, comprising an electric conductor spirally wound on an almost flat surface; a first shield coil for generating a magnetic field for canceling at least partially the magnetic field generated by said main coil in its rear, comprising an electric conductor spirally wound on an almost flat surface in the rear of said main coil; and a second shield coil, extended to the coil conductor arranged at outermost part of said first shield coil and connected to said first shield coil, for generating a magnetic field with a strength distribution which, when combined with the magnetic field generated by said first shield coil, cancels the magnetic field generated by said main coil at its outer edge. 27. A gradient magnetic field coil according to claim 26, wherein said second shield coil is provided by dividing said first shield coil conductor into plural diverging conductors, and the current applied to said first shield coil is split and thus applied to each of said diverging conductors in a predetermined ratio.