MAGNETIC RESONANCE IMAGING DEVICE, MAGNETIC RESONANCE IMAGING METHOD AND SUSCEPTIBILITY CALCULATION PROGRAM
First Claim
1. A magnetic resonance imaging apparatus, comprising,a static magnetic field magnet,a magnetic field generator configured to apply a gradient magnetic field and an RF magnetic field to space formed by the static magnetic field magnet,a receiver configured to receive a nuclear magnetic resonance signal generated from a subject placed in the space, anda computer configured to perform computations on the nuclear magnetic resonance signal, wherein,the computer comprises,a measurement unit configured to control operations of the magnetic field generator and of the receiver, and to measure the nuclear magnetic resonance signal including effects of magnetic field inhomogeneity,an image reconstructor configured to perform image reconstruction by using the nuclear magnetic resonance signal, so as to create a complex image, andan image converter configured to calculate a susceptibility image of the subject, by using the complex image, wherein,the image converter comprises,a magnetic field calculator configured to calculate a magnetic field reflected image from the complex image,a mask calculator configured to use the image created by the image reconstructor to calculate a low-signal region mask associated with a low-signal region, and a plurality of region masks associated with a plurality of regions in a high-signal region, anda susceptibility calculator configured to use the magnetic field reflected image calculated by the magnetic field calculator, the low-signal region mask and the plurality of region masks calculated by the mask calculator, and to calculate susceptibility as to each of the plurality of regions, wherein,the susceptibility calculator calculates the susceptibility of a region different from a specific region, under a first constraint that the low-signal region is set as a background, and a second constraint that the susceptibility of the specific region among the plurality of the regions is set to a specific value.
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Accused Products
Abstract
Accuracy degradation due to a signal loss is reduced, and susceptibility is calculated with high accuracy where, by using an MRI, at least one echo is acquired where spatial magnetic field inhomogeneity is reflected, and a complex image is calculated from the acquired echo. Three masks are calculated from the calculated complex image; a low-signal region mask representing a low signal region, a first high-signal region mask representing a high signal and high fat content region, and a second high-signal region mask representing a high signal and low fat content region. In calculating a susceptibility image from a frequency image or a magnetic field image generated from the complex image, the susceptibility image is obtained under the constraint that a region defined by the low-signal region is set as a background and the susceptibility of the region defined by the second high-signal region mask is set to a specific value.
4 Citations
15 Claims
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1. A magnetic resonance imaging apparatus, comprising,
a static magnetic field magnet, a magnetic field generator configured to apply a gradient magnetic field and an RF magnetic field to space formed by the static magnetic field magnet, a receiver configured to receive a nuclear magnetic resonance signal generated from a subject placed in the space, and a computer configured to perform computations on the nuclear magnetic resonance signal, wherein, the computer comprises, a measurement unit configured to control operations of the magnetic field generator and of the receiver, and to measure the nuclear magnetic resonance signal including effects of magnetic field inhomogeneity, an image reconstructor configured to perform image reconstruction by using the nuclear magnetic resonance signal, so as to create a complex image, and an image converter configured to calculate a susceptibility image of the subject, by using the complex image, wherein, the image converter comprises, a magnetic field calculator configured to calculate a magnetic field reflected image from the complex image, a mask calculator configured to use the image created by the image reconstructor to calculate a low-signal region mask associated with a low-signal region, and a plurality of region masks associated with a plurality of regions in a high-signal region, and a susceptibility calculator configured to use the magnetic field reflected image calculated by the magnetic field calculator, the low-signal region mask and the plurality of region masks calculated by the mask calculator, and to calculate susceptibility as to each of the plurality of regions, wherein, the susceptibility calculator calculates the susceptibility of a region different from a specific region, under a first constraint that the low-signal region is set as a background, and a second constraint that the susceptibility of the specific region among the plurality of the regions is set to a specific value.
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10. A magnetic resonance imaging method, comprising,
measuring a nuclear magnetic resonance signal including effects of magnetic field inhomogeneity, creating a complex image by using the nuclear magnetic resonance signal, and creating a magnetic field reflected image by using the complex image, and creating a susceptibility image by using the magnetic field reflected image, wherein, a low-signal region mask and a high-signal mask are generated by using an absolute value image created from the complex image, and a first region mask and a second region mask are created from the high-signal mask, the first region mask representing a first region where a pixel value of a certain discriminant image is larger than a predetermined threshold and the second region mask representing a second region where the pixel value of the discriminant image is equal to or smaller than the predetermined threshold, and by using the magnetic field reflected image, the low-signal region mask, and the first and the second region masks, susceptibility of the first region is calculated under a first constraint that a region defined by the low-signal region mask is set as a background, and a second constraint that the susceptibility of the second region is set to a specific value, and a second region susceptibility image is calculated under the constraint that the region defined by the low-signal region mask and the first region are set as the background.
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15. A susceptibility calculation program causing a computer to implement,
creating a complex image using a nuclear magnetic resonance signal including effects of magnetic field inhomogeneity, measured by a magnetic resonance imaging apparatus, creating a magnetic field reflected image by using the complex image, creating an absolute value image from the complex image, creating a low-signal region mask and a high-signal mask by using the absolute value image, and further creating from the high-signal mask, a plurality of region masks associated with a plurality of regions, calculating the first susceptibility of a region excluding a specific region, by using the magnetic field reflected image, the low-signal region mask, and the plurality of region masks, under a first constraint that a region defined by the low-signal mask is set as a background, and a second constraint that the susceptibility of the specific region among the plurality of regions is set to a specific value, calculating the second susceptibility of the specific region, under a third constraint for setting as the background, the region defined by the low-signal region mask and the region defined by the region mask associated with a region excluding the specific region, and combining the first susceptibility and the second susceptibility.
Specification