Abstract: An MR system comprising an improved gradient coil that does not compromise patient comfort is disclosed herein. The MR system is either a bore-type or a gap-type system and comprises a main magnet (102, 502) arranged to generate a main magnetic field; an examination region (118, 518) having a central axis (114)—in a bore-type system—or a central plane (514)—in a gap-type system—that is either parallel (for a bore-type MR system) or perpendicular (for a gap-type MR system) to the direction of the main magnetic field; and a gradient coil for generating a magnetic field gradient across the examination region, wherein the gradient coil comprises a first coil portion (108a, 508a) and a second coil portion (108b, 508b) located at different distances from the central axis (in a bore-type system) or from the central plane (in a gap-type system).

Abstract: The invention relates to a magnetic resonance imaging system which comprises means for generating a static magnetic field and a gradient coils system for generating a time varying magnetic gradient field by use of a first electrical current and a second electrical current. The gradient coils system is located in the magnetic field and the gradient coils system has a plurality of vibrational modes. Lorentz forces are generated due to the interaction of the first and/or second electrical currents with the superposition of the static magnetic field and the magnetic gradient field. The gradient coils system and/or the first electrical current are adapted so that the integral of the in-products of said Lorentz forces and a vibrational mode of said plurality of vibrational modes is at a value close to zero, wherein said in-products are determined for all points of the gradient coils system, and wherein the integral is determined by summing the in-products determined for all the points.

Abstract: The present invention relates to a magnetic resonance imaging (MRI) device and to a method for operating it. The basic components of an MRI device are the main magnet system (2) for generating a steady magnetic field, the gradient system (3) with at least one gradient coil, the RF system and the signal processing system. According to the present invention, the gradient coil is split into sub-coils (S1, S2) at least in the direction of the steady magnetic field. By doing so, the amplitude of the non-imaging component of the gradient field in the vicinity of the patient is reduced, leading to reduced peripheral nerve stimulation and thus enhanced image quality.

Abstract: A novel method is described for simulation of an electric stimulation of the nerve system subject to the rate of change of gradient fields. A gradient signal is filtered and a stimulation signal is derived, which is compared with a predetermined stimulation threshold value. An indicator signal is generated if the threshold value is exceeded. Therefore the time dependent and spatially dependent electric fields as defined by the scanning sequence and the gradient coil properties are calculated. A vector combination of said calculated electric field components from each gradient coil axis is performed, which results in a temporal diagram of the total electric field at various spatial locations within the gradient coil. The stimulation probability at each location from said temporal diagram and said stimulation signal is then calculated, and said stimulation probability is compared with the stimulation threshold value at each location within the gradient coil.

Abstract: Gradient fields Gx=∂Bz/∂x etc. are generated in an MRI apparatus in order to indicate the position (x, y, z) of an object pixel to be imaged. In a known MRI system the x and y gradient fields are generated by a combination of four gradient coils, two of which are intended to receive the x and y gradient signals whereas the other two coils are intended to receive a mix of the x and y gradient signals in order to enable a simpler structure of the gradient coils and easier impedance matching. According to the invention, apart from the x, y and z gradient signals, other signals are applied to a conversion system (35) in order to realize the desired gradient fields but also to achieve degrees of freedom that can be used for optimizing system parameters such as heat dissipation or the uniformity of the distribution of power among the gradient amplifiers.

Abstract: Gradient fields Gx=∂Bz/∂x etc. are generated in an MRI apparatus in order to indicate the position (x, y, z) of an object pixel to be imaged. In a known MRI system the x and y gradient fields are generated by a combination of four gradient coils, two of which are intended to receive the x and y gradient signals whereas the other two coils are intended to receive a mix of the x and y gradient signals in order to enable a simpler structure of the gradient coils and easier impedance matching. According to the invention, apart from the x, y and z gradient signals, other signals are applied to a conversion system (35) in order to realize the desired gradient fields but also to achieve degrees of freedom that can be used for optimizing system parameters such as heat dissipation or the uniformity of the distribution of power among the gradient amplifiers.