Kabushiki Kaisha Toshiba

Toshiba Medical Systems Corporation

Hiromi Kawamoto

Masafumi Kondo

Hitoshi Yamagata

Kazuhiro Iinuma

Yoshitomo Sakakura

Motohiro Miura

Takeshi Toyoshima

Ayumi Katsunuma

Yasuhiro Uosaki

Hiromitu Takamori

Daihachirou Tsuruno

Osamu Fujitsuka

A magnetic resonance imaging apparatus includes; a gradient coil that applies a gradient magnetic field to a static magnetic field in which an examined subject is placed; a metal shim with which the gradient coil is provided and that corrects spatial nonuniformity of the static magnetic field; an executing unit that executes an imaging sequence; and a controlling unit that, before execution of the imaging sequence is started, raises the temperature of the metal shim up to a saturation temperature that is to be reached during the execution of the imaging sequence.

Magnetic resonance imaging apparatus

A passive shim coil is disposed in a magnetic resonance imaging (MRI) apparatus for shielding magnetic flux of a gradient magnetic field at an inner circumference side generated by a gradient coil, and is set at an outer circumference side of the gradient coil. The coil body is formed of a portion including a superconducting material and a portion including a non-superconducting material.

Magnetic resonance imaging apparatus, shield coil, manufacturing method of shield coil, and driving method of magnetic resonance imaging apparatus

Although magnet coil windings are distributed discontinuously, the distribution of magnetic fields generated actually approaches a desired continuous distribution. The desired continuous distribution is defined analytically, as closely as possible. A system for acquiring magnetic resonance data has a coil segment formed by winding a conductor on a bobbin representing an axial direction. A magnetic field is generated by supplying current into the conductor. Winding positions at which the conductor is wound turn-by-turn on the bobbin are determined in agreement with a specified current step value and sequentially from a winding positioned at an outermost end of the coil segment in the axial direction. Additionally, a shunt element for shunting the current carried turn-by-turn is arranged in the coil segment in relation to a pattern of turns of the coil segment by winding the conductor into a plurality of current flows through a plurality of shunt paths.

Arrangement of coil windings for MR systems

Solid-borne vibrations and airborne vibrations from a gradient coil unit in an MRI gantry environment are markedly reduced thereby reducing ambient noise occurring due to the vibrations. Support assemblies retain the gradient coil unit in a mechanically-uncoupled or substantially-uncoupled state relative to the magnet by supporting the coil unit at separate positions on the floor (e.g., with anchor bolts rigidly coupling coil support assemblies to the floor). Moreover, the gradient coil unit and at least parts of the support assemblies may be retained in a vacuum space.

Magnetic resonance imaging system having mechanically decoupled field

In a magnetic resonance imaging apparatus, gradient magnetic fields and a radiofrequency magnetic field are applied to a subject placed in a static magnetic field to excite nucleuses and generate magnetic resonance signals. A magnetic resonance image is reconstructed on the basis of the magnetic resonance signals. The gradient magnetic fields are produced by gradient coils. A very high-speed imaging method such as an echo planar method requires shield coils to magnetically shield, to the outside, the magnetic fields generated by the primary coils. It is very difficult to drive the primary coils and the shield coils by one amplifier to raise gradient magnetic fields having a relatively high strength within a short period of time. The primary coils and the shield coils are divided into a plurality of groups, and currents are individually supplied to the plurality of groups to allow to raise the gradient magnetic fields having a relatively high strength within the short period of time.

An MRI system is provided for improving the magnetic coupling and positional relationship between gradient coils and shim coils, thus simplifying positioning of the coils (retention of orthogonality), designing an MRI system compactly, and reducing cost. An MRI system comprises a magnet generating a static magnetic field and a gradient coil unit generating a gradient magnetic field superposed on the static magnetic field. The gradient coil unit is formed into a substantially cylindrical shape having an outer circumferential surface, and shields the gradient magnetic field from being leaked out into a radially outer space. The MRI system further comprises a shim coil unit generating a correcting magnetic field homogenizing the static magnetic field. The shim coil unit is mounted on the outer circumferential surface of the gradient coil unit in common serving as a bobbin for the shim coil unit.

Shimming in magnetic resonance imaging

A nuclear magnetic resonance imaging with improved image quality and operation efficiency. It uses an active shield coil with an outer shielding coil having at least two coil turns which are provided on a plurality of separate layers and mutually connected electrically, in order to reduce the heat generation. The eddy current in the shielding coil is reduced by providing a slit portion thereon. The eddy current compensation is achieved by using an appropriate eddy current compensation pulse to minimize a residual eddy current magnetic field within a desired field of view according to a model of a general expression of the residual eddy current magnetic field after the eddy current compensation. The optimum setting of the system parameters for various imaging pulse sequences is achieved for the undetermined gradient coil configuration as well as for the predetermined gradient coil configuration, according to a mathematical model analysis of various imaging pulse sequences.

Nuclear magnetic resonance imaging with improved image quality and

The MR imaging apparatus comprises an RF shield for interposed between the set of gradient coil and the RF coil. The RF shield is a cylinder which longitudinal axis is substantially coincident to the z-axis in which a static magnetical field is applied. The RF shield comprises two conductive sheet-members which are half-cylinder respectively and integrated into one cylinder. The sheet members have a plurality of generally C-shaped conductive loop portions respectively which are defined by nonconductive lines parallel to RF current flow induced therein by the RF coil and a single radial cut line respectively. The RF shield comprises a connecting means for electrically connecting the C-shaped conductive loop portions so that the C-shaped conductive loop portion in one of the sheet members and corresponding C-shaped conductive loop portion in the other sheet member can be formed into one circuit respectively and a current can circulate in said circuit in the same direction around a y-axis orthogonal to the z-axis.

In an MR (magnetic resonance) imaging method, not only eddy current field is compensated, but also a gradient field vibrated by a mechanical vibration caused by the eddy current is compensated. The method for imaging a biological body under medical examination by utilizing a magnetic resonance phenomenon under influence of a static magnetic field and a gradient magnetic field to acquire an MR image of a preselected slice portion within the biological body, comprising the steps of: producing a first drive current on which an eddy current field compensating current has been superimposed: producing a vibrating-field compensating current for compensating a gradient field vibrated by the eddy current; and superimposing the vibrating-field compensating current on the first drive current to obtain a second drive current. The second drive current is supplied to a gradient coil assembly for generating a gradient field whose vibrating field component has been compensated.

Magnetic resonance imaging method and apparatus capable of compensating

A magnetic resonance imaging system comprises a static field generating section for generating a static field applied to an object, a gradient field application section for applying a gradient field in the form of a pulse to the object disposed in the static field, a high frequency wave transmitting/receiving section for applying an excitation pulse of a high frequency field to the object disposed in the static field and for detecting a magnetic resonance signal excited in the object, and a controlling/processing section for driving the gradient field application section and high frequency wave transmitting/receiving section at a predetermined timing and for processing the magnetic resonance signal to obtain magnetic resonance image data. The system further comprises at least one auxiliary coil, and a current supply section for supplying a current for compensating to the auxiliary coil.

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Yaita, Japan

Hiromi Kawamoto