Magnetic resonance imaging apparatus and eddy current compensation method

Patent metadata

Field	Value
Publication number	US-9297876-B2
Application number	US-201013377275-A
Country	US
Kind code	B2
Filing date	Jun 4, 2010
Priority date	Jun 10, 2009
Publication date	Mar 29, 2016
Grant date	Mar 29, 2016

Abstract

An object is to correct a magnetic field caused by an eddy current, which is generated due to application of a gradient magnetic field, not only in the application direction of the gradient magnetic field but also in a direction different from the application direction of the gradient magnetic field. In the present invention, in order to achieve this object, a compensation magnetic field which compensates for an eddy current magnetic field generated in each of an application direction of a test gradient magnetic field and a direction different from the application direction in each direction is calculated using the test gradient magnetic field. When generating an arbitrary gradient magnetic field, a compensation magnetic field which compensates for an eddy current magnetic field according to application of an arbitrary gradient magnetic field on the basis of the measured eddy current magnetic field in each direction is generated together with the arbitrary gradient magnetic field.

First claim

The invention claimed is:

1. A magnetic resonance imaging apparatus comprising:
a gradient magnetic field generating unit that generates an arbitrary gradient magnetic field;
an eddy current magnetic field measuring unit that measures an eddy current magnetic field based on an eddy current, which is generated according to application of a test gradient magnetic field, through a phase of an image; and
a compensation magnetic field calculating unit that calculates a compensation magnetic field, which is for compensating for an eddy current magnetic field according to application of the arbitrary gradient magnetic field, on the basis of the measured eddy current magnetic field,
wherein the gradient magnetic field generating unit generates the compensation magnetic field in addition to the arbitrary gradient magnetic field,
wherein the eddy current magnetic field measuring unit reconstructs three-dimensional images from echo signals measured by changing a polarity of the test gradient magnetic field, acquires a three-dimensional phase difference image by calculating a difference between phase images of two three-dimensional images, and measures the eddy current magnetic field generated in each direction amongst an application direction of the test gradient magnetic field and another direction which is different from the application direction, on the basis of a difference between phases in two points or regions in each of said application direction and said another direction, in a pair of planes in the three-dimensional phase difference image,
the compensation magnetic field calculating unit calculates the compensation magnetic field, which compensates for the eddy current magnetic field according to the application of the arbitrary gradient magnetic field, and distributes the calculated compensation magnetic field in each application direction of the gradient magnetic field, on the basis of the measured eddy current magnetic field in said each direction, and
the gradient magnetic field generating unit generates the calculated compensation magnetic field distributed in said each application direction of the gradient magnetic field, together with the arbitrary gradient magnetic field.

2. The magnetic resonance imaging apparatus according to claim 1 ,
wherein the compensation magnetic field calculating unit calculates a plurality of compensation parameters specifying the compensation magnetic field, and
the gradient magnetic field generating unit generates the compensation magnetic field on the basis of the plurality of compensation parameters.

3. A magnetic resonance imaging apparatus comprising:
a gradient magnetic field generating unit that generates a gradient magnetic field;
a measurement control unit that controls the gradient magnetic field generating unit to apply to a subject a gradient magnetic field specified in a predetermined pulse sequence and controls measurement of an echo signal from the subject; and
an arithmetic processing unit that performs arithmetic processing of the echo signal to reconstruct an image of the subject,
wherein the measurement control unit makes the gradient magnetic field generating unit generate a compensation magnetic field, which compensates for an eddy current magnetic field based on an eddy current generated according to application of the gradient magnetic field, together with the gradient magnetic field,
the arithmetic processing unit reconstructs a phase image using an echo signal measured by application of a test gradient magnetic field, calculates eddy current magnetic fields generated in an application direction of the test gradient magnetic field and a direction different from the application direction on the basis of the phase image, and calculates a compensation magnetic field, which compensates for an eddy current magnetic field according to application of an arbitrary gradient magnetic field in each direction, on the basis of the calculated eddy current magnetic field in each direction, and
the measurement control unit controls the gradient magnetic field generating unit to generate the calculated compensation magnetic field in each direction together with the arbitrary gradient magnetic field, and
wherein the measurement control unit reconstructs three-dimensional images from echo signals measured by changing a polarity of the gradient magnetic field, acquires a three-dimensional phase difference image by calculating a difference between phase images of two three-dimensional images, and measures the eddy current magnetic field generated in each direction amongst an application direction of the gradient magnetic field and another direction which is different from the application direction, on the basis of a difference between phases in two points or regions in each of said application direction and said another direction, in a pair of planes in the three-dimensional phase difference image,
the measurement control unit calculates the compensation magnetic field, which compensates for the eddy current magnetic field according to the application of the arbitrary gradient magnetic field, and distributes the calculated compensation magnetic field in each application direction of the gradient magnetic field, on the basis of the measured eddy current magnetic field in said each direction, and
the gradient magnetic field generating unit generates the calculated compensation magnetic field distributed in said each application direction of the gradient magnetic field, together with the arbitrary gradient magnetic field.

4. A magnetic resonance imaging apparatus comprising:
a gradient magnetic field generating unit that generates an arbitrary gradient magnetic field;
an eddy current magnetic field measuring unit that measures an eddy current magnetic field based on an eddy current, which is generated according to application of a test gradient magnetic field, through a phase of an image; and
a compensation magnetic field calculating unit that calculates a compensation magnetic field, which is for compensating for an eddy current magnetic field according to application of the arbitrary gradient magnetic field, on the basis of the measured eddy current magnetic field,
wherein the gradient magnetic field generating unit generates the compensation magnetic field in addition to the arbitrary gradient magnetic field,
wherein the eddy current magnetic field measuring unit reconstructs three-dimensional images from echo signals measured by changing a polarity of the test gradient magnetic field, acquires a three-dimensional phase difference image by calculating a difference between phase images of two three-dimensional images, and measures the eddy current magnetic field generated in each direction amongst an application direction of the test gradient magnetic field and another direction which is different from the application direction, on the basis of a difference between phases in two points or regions in each of said application direction and said another direction, in a pair of planes in the three-dimensional phase difference image,
the compensation magnetic field calculating unit calculates the compensation magnetic field in each application direction of the gradient magnetic field, which compensates for the eddy current magnetic field according to the application of the arbitrary gradient magnetic field, on the basis of the measured eddy current magnetic field in said each direction, and
the gradient magnetic field generating unit generates the calculated compensation magnetic field distributed in said each application direction of the gradient magnetic field, together with the arbitrary gradient magnetic field.

5. A magnetic resonance imaging apparatus comprising:
a gradient magnetic field generating unit that generates an arbitrary gradient magnetic field;
an edd

Assignees

• Kaneta Akiko
• Takeuchi Hiroyuki
• Miyawaki Shouichi
• Hitachi Medical Corp

Inventors

• Kaneta Akiko
• Takeuchi Hiroyuki
• Miyawaki Shouichi

Classifications

• G01R33/56518 Primary

  due to eddy currents, e.g. caused by switching of the gradient magnetic field · CPC title