Image processing device, image processing method, image processing program, and magnetic resonance imaging device
Magnetic susceptibility is calculated with high accuracy without significant increase of calculation time. Provided is an image processing device comprising an image processor for creating a susceptibility image representing a magnetic susceptibility of at least one tissue of the subject, from an image created on the basis of magnetic resonance signals generated from a subject, wherein the image processor includes an image separator configured to separate from the image, a specific tissue image representing a content of a predetermined specific tissue and a frequency image, an adder-subtractor configured to calculate a post-subtraction frequency image obtained by subtracting from the frequency image, frequency change caused by the specific tissue, and an image converter configured to calculate a specific susceptibility image representing the magnetic susceptibility of the specific tissue on the basis of the specific tissue image, and to calculate a post-subtraction susceptibility image on the basis of the post-subtraction frequency image.
1. An image processing device for creating a susceptibility image representing a magnetic susceptibility of at least one tissue in a subject, from an image created on the basis of magnetic resonance signals generated from the subject, the image processing device comprising:
an image separator configured to separate from the image, a specific tissue image related to a predetermined specific tissue and a frequency image;
an adder-subtractor configured to calculate a post-subtraction frequency image obtained by subtracting frequency change caused by the specific tissue, from the frequency image; and
an image converter configured to calculate a specific susceptibility image representing the magnetic susceptibility of the specific tissue on the basis of the specific tissue image, and to calculate a post-subtraction susceptibility image on the basis of the post-subtraction frequency image.
2. The image processing device according to claim 1 , wherein,
the adder-subtractor adds the post-subtraction susceptibility image to the specific susceptibility image, thereby creating a susceptibility image representing the magnetic susceptibilities of two or more tissues in the subject.
3. The image processing device according to claim 1 , wherein,
the image separator calculates a specific tissue content image representing a content of the specific tissue on the basis of the specific tissue image, and
the image converter calculates the specific susceptibility image representing the magnetic susceptibility of the specific tissue on the basis of the specific tissue content image.
4. The image processing device according to claim 3 , wherein,
the image converter calculates the specific susceptibility image by multiplying the specific tissue content image by a specific factor calculated by Equation 1:
[Equation 1]
χ WF =arg min χ ∥ML (δ− C χ R )∥ 2 2 (1)
where χ WF is the specific factor, M is a mask image representing a region for obtaining signals, L is the Laplace operator, δ is a magnetic field image calculated from the frequency image, C is a matrix corresponding to convolution calculation for χ, and R is the specific tissue content image.
5. The image processing device according to claim 1 , wherein,
the specific tissue is fat,
the image separator calculates a fat image as the specific tissue image, and
the image converter calculates a fat susceptibility image as the specific susceptibility image.
6. The image processing device according to claim 1 , wherein,
the specific tissue includes at least any one of fat, a hemorrhage region, a vein, and basal ganglia.
7. An image processing method for creating a susceptibility image representing a magnetic susceptibility of at least one tissue in a subject, from an image created on the basis of magnetic resonance signals generated from the subject, the image processing method comprising:
an image separation step for separating from the image, a specific tissue image representing a content of a predetermined specific tissue and a frequency image;
a computational processing step for calculating a post-subtraction frequency image obtained by subtracting from the frequency image, frequency change caused by the specific tissue; and
an image conversion step for calculating a specific susceptibility image representing the magnetic susceptibility of the specific tissue on the basis of the specific tissue image, and calculating a post-subtraction susceptibility image on the basis of the post-subtraction frequency image.
8. A non-transitory computer-readable storage medium storing an image processing program, which when executed by a processor, causes a computer to implement creation of a susceptibility image representing a magnetic susceptibility of at least one tissue in a subject, from an image created on the basis of magnetic resonance signals generated from the subject, and further causes the computer to perform:
an image separation step for separating from the image, a specific tissue image representing a content of a predetermined specific tissue and a frequency image;
a computational processing step for calculating a post-subtraction frequency image obtained by subtracting from the frequency image, frequency change caused by the specific tissue; and
an image conversion step for calculating a specific susceptibility image representing the magnetic susceptibility of the specific tissue on the basis of the specific tissue image, and calculating a post-subtraction susceptibility image on the basis of the post-subtraction frequency image.
9. A magnetic resonance imaging apparatus comprising:
a measurement unit configured to measure a magnetic resonance signal generated from a subject, by applying an RF magnetic field pulse and a gradient magnetic field to the subject placed in a static magnetic field;
an image reconstructor configured to reconstruct an image on the basis of the magnetic resonance signal; and
an image processor configured to create from the image, a susceptibility image representing a magnetic susceptibility of at least one tissue of the subject, wherein
the image processor comprises:
an image separator configured to separate from the image, a specific tissue image representing a content of a predetermined specific tissue and a frequency image;
an adder-subtractor configured to calculate a post-subtraction frequency image obtained by subtracting from the frequency image, frequency change caused by the specific tissue; and
an image converter configured to calculate a specific susceptibility image representing the magnetic susceptibility of the specific tissue on the basis of the specific tissue image, and to calculate a post-subtraction susceptibility image on the basis of the post-subtraction frequency image.