Abstract: A gradient coil for magnetic resonance imaging (MRI) has an elliptic cylindrical first coil and a second coil arranged coaxially to the first coil. The second coil is located outside the first coil in the radial direction thereof. The second coil is either elliptic-cylindrical or cylindrical. Winding positions of wires of the second coil are determined so that a magnetic field created outside the second coil by the first coil is cancelled out. Practically, circumferential current densities of the first and second coils are expressed by weighted even and odd functions. Ratios between weights of the second and first coils are then determined on values derived from the number of waves in the coil axial direction and a flatness rate of the ellipse. The winding positions of wires of the second coil are determined on the values.

Abstract: A gradient coil for magnetic resonance imaging (MRI) ha an elliptic cylindrical first coil and a second coil arranged coaxially to the first coil. The second coil is located outside the first coil in the radial direction thereof. The second coil is either elliptic-cylindrical or cylindrical winding positions of wires of the second coil are determined so that a magnetic field created outside the second coil by the first coil is cancelled out. Practically, circumferential current densities of the first and second coils are expressed by weighted even and odd functions. Ratios between weights of the second and first coils are then determined on values derived from the number of waves in the coil axial direction and a flatness rate of the ellipse. The winding positions of wires of the second coil are determined on the values.

Abstract: A magnetic resonance imaging apparatus generates an MR signal from an object by applying a gradient field pulse generated by a gradient field coil and a high-frequency magnetic field pulse generated by a high-frequency coil to the object in a static field, and reconstructs an image on the basis of the MR signal. The gradient field coil is housed in a sealed vessel. The internal air in the sealed vessel is exhausted by the pump to prevent noise. By controlling the operation of the pump using a control circuit, noise in imaging operation can be reduced more effectively.

Abstract: An active shield type gradient coil apparatus comprises main coils for generating a gradient magnetic field and shield coils for generating a magnetic field to reduce the leak magnetic field from the main coils. In the active shield type gradient coil apparatus, a stimulation output section for outputting stimulation to a subject is incorporated. In this incorporation, the main coils are arranged at the outside of an area sandwiched between the stimulation output section and the subject such that the simulation can be transmitted to the subject from the stimulation output section without being blocked by the main coils. By this arrangement, both the use of the active shield type as the gradient coil apparatus and good transmission of stimulation to the subject can be realized.

Abstract: A nuclear magnetic resonance imaging apparatus using asymmetric torque-free active shield gradient coils for realizing a sufficient imaging field of view, a sufficient eddy current magnetic field suppression effect, and a substantially complete torque cancellation. The gradient coil is formed by: a primary coil having an asymmetric current distribution in which all current returns are asymmetrically arranged toward one side of the primary coil, a shield coil having a current distribution for cancelling out a leakage magnetic field generated by the asymmetric current distribution of the primary coil, and a torque cancellation coil, provided adjacent to the primary coil and the shield coil, having a current distribution for cancelling out a torque acting on the primary coil and the shield coil in a static magnetic field. The primary coil generates the gradient magnetic field which cancels out a gradient field contribution from the torque cancellation coil to produce a desired gradient magnetic field.

Abstract: An active shield gradient coil for a nuclear magnetic resonance imaging, formed by a primary coil having a fingerprint shaped current distribution formed on an inner cylinder in which at least a part of current return lines is cut out, a shield coil having a current distribution formed on an outer cylinder, and a bridging connection member for connecting cut out part of the current return lines of the primary coil with the shield coil, in which the current distribution of the shield coil is a composition of a first shield pattern for cancelling out a magnetic field produced by the primary coil outside the outer cylinder and a second shield pattern for cancelling out a magnetic field produced by the bridging connection member outside the outer cylinder. The current distribution of the primary coil can have turn back current paths for leading the cut out part of the current return lines on one end of the gradient coil to another end of the gradient coil.