Magnetic resonance imaging device and sensitivity distribution calculation program
During obtaining a sensitivity distribution in a k-space, data based on which the sensitivity distribution is obtained is expanded with a mirror image to create an expanded image to prevent spectrum leakage, and the sensitivity distribution is stably calculated. During obtaining the sensitivity distribution in the k-space, image data based on which the sensitivity distribution is obtained is inverted as a mirror image to be made into the expanded image, the expanded image is transformed into k-space data, and a frequency component (frequency space data) of the sensitivity distribution is calculated. A region corresponding to the original image data is clipped from the calculated frequency space data, and the sensitivity distribution is obtained.
1. A magnetic resonance imaging device comprising:
a measurement unit that is provided with a receiving coil having a plurality of channels and is configured to measure a nuclear magnetic resonance signal of a subject for each channel of the receiving coil; and
an image calculation unit configured to create an image of the subject using a sensitivity distribution for each channel of the receiving coil and a channel image generated based on the nuclear magnetic resonance signal for each channel measured by the measurement unit, wherein
the image calculation unit includes a sensitivity distribution calculation unit configured to calculate a sensitivity distribution for each channel of the receiving coil in a k-space using an image obtained for sensitivity distribution, and
the sensitivity distribution calculation unit includes an expanded image creation unit configured to generate, by executing one or more inversion processes on at least a part of the image for obtaining sensitivity distribution, an expanded image obtained by combining the image for obtaining sensitivity distribution and an inverted image, and calculates the sensitivity distribution using the expanded image.
2. The magnetic resonance imaging device according to claim 1 , wherein
the expanded image creation unit is configured to generate, as the inverted image, a mirror image obtained by inverting the entire image.
3. The magnetic resonance imaging device according to claim 1 , wherein
the expanded image creation unit is configured to form, as the inverted image, a partial mirror image obtained by inverting a region excluding an end portion region of the image, and connect the partial mirror image to an end of the original image for obtaining sensitivity distribution to generate the expanded image.
4. The magnetic resonance imaging device according to claim 1 , wherein
the expanded image creation unit is configured to execute one or more inversion processes after enlarging a periphery of the image for obtaining sensitivity distribution by zero fill.
5. The magnetic resonance imaging device according to claim 1 , wherein
the sensitivity distribution calculation unit is configured to calculate the sensitivity distribution using a region in the k-space corresponding to a region of the original image for obtaining sensitivity distribution in the expanded image.
6. The magnetic resonance imaging device according to claim 1 , wherein
the image for obtaining sensitivity distribution is a three-dimensional image, and
the sensitivity distribution calculation unit further includes a slice clipping unit configured to clip a two-dimensional image for obtaining sensitivity distribution from the three-dimensional image for obtaining sensitivity distribution, and is configured to calculate the sensitivity distribution for each slice.
7. The magnetic resonance imaging device according to claim 6 , wherein
the slice clipping unit is configured to clip the two-dimensional image for obtaining sensitivity distribution so as to provide the same FOV as an FOV of the image of the subject created by the image calculation unit.
8. The magnetic resonance imaging device according to claim 1 , wherein
the image for obtaining sensitivity distribution is a three-dimensional image, and
the expanded image creation unit is configured to
execute an inversion process on the three-dimensional image, and
create a three-dimensional expanded image obtained by expanding the three-dimensional image in a three-dimensional direction.
9. The magnetic resonance imaging device according to claim 1 , wherein
the image for obtaining sensitivity distribution includes a reference image and a channel image generated based on a nuclear magnetic resonance signal for each channel, and
the measurement unit further includes, as the receiving coil, a wide-region receiving coil configured to measure a nuclear magnetic resonance signal for the reference image.
10. The magnetic resonance imaging device according to claim 1 , wherein
the image for obtaining sensitivity distribution includes a reference image and a channel image generated based on a nuclear magnetic resonance signal for each channel, and
the image calculation unit further includes an image synthesis unit configured to synthesize the channel image to generate the reference image.
11. The magnetic resonance imaging device according to claim 1 , wherein
the sensitivity distribution calculation unit is configured to calculate, as the sensitivity distribution, a weight of sensitivity distribution data for each channel with respect to all the channels, and
the image calculation unit is configured to execute image reconstruction based on a GRAPPA method using a sensitivity distribution including a weight in the k-space of each channel for the nuclear magnetic resonance signal measured for each channel.
12. A sensitivity distribution calculation program for calculating a sensitivity distribution for each channel of a magnetic resonance imaging device provided with a receiving coil including a plurality of channels by processing a nuclear magnetic resonance signal measured in each channel, the sensitivity distribution calculation program causing a computer to execute steps of
reading an image for obtaining sensitivity distribution including a reference image and a channel image, or generating the image for obtaining sensitivity distribution based on a nuclear magnetic resonance signal acquired by the magnetic resonance imaging device,
executing one or more inversion processes on at least a part of the image for obtaining sensitivity distribution, and generating an expanded image for each of the reference image and the channel image by combining a generated inverted image and the original image for obtaining sensitivity distribution,
executing inverse Fourier transform on the expanded image to generate k-space data, and
calculating a sensitivity distribution for each channel based on the expanded image in the k-space.
13. The sensitivity distribution calculation program according to claim 12 , wherein
the image for obtaining sensitivity distribution is three-dimensional data, and
the steps further comprise a step of clipping a two-dimensional image for obtaining sensitivity distribution from the three-dimensional data.
14. The sensitivity distribution calculation program according to claim 12 , wherein
the step of calculating a sensitivity distribution further includes a step of removing peripheral noise of the sensitivity distribution calculated for each channel.