Magnetic resonance imaging device, and method for generating magnetic susceptibility enhanced image

• US 9,165,386 B2
• Filed: 10/03/2012
• Issued: 10/20/2015
• Est. Priority Date: 10/12/2011
• Status: Active Grant

• Current Assignee: FUJIFILM Healthcare Corp. (Fujifilm Holdings Corporation)
• Original Assignee: Hitachi, Ltd.
• Inventors: Sato, Ryota, Shirai, Toru, Taniguchi, Yo, Soutome, Yoshihisa, Bito, Yoshitaka
• Primary Examiner(s): Harandi, Siamak
• Application Number:
  US14/342,186
• Publication Number:
  US 20140219533A1
• Time in Patent Office: 1,112 Days
• Field of Search: None
• US Class Current: 1/1
• CPC Class Codes: A61B 5/055 involving electronic [EMR] or nuclear [NMR] magnetic resonance, e.g. magnetic resonance imaging
• CPC Class Codes: G01R 33/24 for measuring direction or magnitude of magnetic fields or magnetic flux
• CPC Class Codes: G01R 33/5608 Data processing and visualization specially adapted for MR, e.g. for feature analysis and pattern recognition on the basis of measured MR data, segmentation of measured MR data, edge contour detection on the basis of measured MR data, for enhancing measured MR data in terms of signal-to-noise ratio by means of noise filtering or apodization, for enhancing measured MR data in terms of resolution by means for deblurring, windowing, zero filling, or generation of gray-scaled images, colour-coded images or images displaying vectors instead of pixels image data processing or generation, in general G06T
• CPC Class Codes: G01R 33/5613 Generating steady state signals, e.g. low flip angle sequences [FLASH]
• CPC Class Codes: G01R 33/5635 Angiography, e.g. contrast-enhanced angiography [CE-MRA] or time-of-flight angiography [TOF-MRA]
• CPC Class Codes: G01R 33/56536 due to magnetic susceptibility variations
• CPC Class Codes: G06T 11/008 Specific post-processing after tomographic reconstruction, e.g. voxelisation, metal artifact correction
• CPC Class Codes: G06T 2207/10088 Magnetic resonance imaging [MRI]
• CPC Class Codes: G06T 2207/30016 Brain
• CPC Class Codes: G06T 5/00 Image enhancement or restoration

Abstract

There is provided a technique for obtaining a magnetic susceptibility-weighted image in which contrast difference of a tissue of interest and a surrounding tissue can be emphasized regardless of the positional relationship of the B₀ direction and the imaging slice. A phase image is converted into a susceptibility map not depending on the B₀ direction, and then a weighting image used for weighting is generated by using the susceptibility map. The weighting image to be generated is for emphasizing contrast of a tissue of interest and a surrounding tissue depending on the purpose. Then, by multiplication of the weighting image and an absolute image, a magnetic susceptibility-weighted image in which the magnetic susceptibility difference is emphasized depending on the purpose is obtained.

Claims

1. A magnetic resonance imaging apparatus comprising a measurement part for applying a radio frequency magnetic field and a gradient magnetic field to a subject placed in a static magnetic field and detecting magnetic resonance signals generated from the subject as complex signals, an operation part for performing an operation for the complex signals to generate an image, and a display processing part for displaying the generated image on a display device, wherein:

the operation part comprises;

an image reconstruction part for reconstructing a complex image in which pixel values are complex numbers from the complex signals, and

an image conversion part for converting the complex image into a magnetic susceptibility-weighted image, and

the image conversion part comprises;

a complex image conversion part for generating an absolute image and a phase image from absolute value components and phase components of the complex numbers of pixels of the complex image, respectively,

a magnetic field image generation part for generating a magnetic field image representing spatial distribution of magnetic field intensity from the phase image,

a susceptibility map generation part for generating a susceptibility map from the magnetic field image,

a weighting image generation part for generating a weighting image for performing weighting for emphasizing contrast difference of a tissue of interest and a surrounding tissue from the susceptibility map, and

a magnetic susceptibility-weighted image generation part for generating a magnetic susceptibility-weighted image by multiplication of the absolute image and the weighting image.

2. The magnetic resonance imaging apparatus according to claim 1, wherein:

the weighting image is a magnetic susceptibility weighting image for emphasizing magnetic susceptibility difference.

3. The magnetic resonance imaging apparatus according to claim 2, wherein:

the weighting image generation part comprises;

a threshold value determination part for determining one or more magnetic susceptibility threshold values on the basis of luminance values of the susceptibility map, and

a weighting image calculation part for calculating the weighting image from the susceptibility map and the magnetic susceptibility threshold value or values determined by the threshold value determination part.

4. The magnetic resonance imaging apparatus according to claim 3, wherein:

the threshold value determination part determines a first magnetic susceptibility threshold value and a second magnetic susceptibility threshold value having a value larger than the first magnetic susceptibility threshold value on the basis of the luminance values of the susceptibility map, and

the weighting image calculation part sets, as for the pixels of the susceptibility map, weights of the pixels having a luminance value smaller than the first magnetic susceptibility threshold value to be a predetermined first weight value, weights of the pixels having a luminance value larger than the second magnetic susceptibility threshold value to be a predetermined second weight value different from the first weight value, and weights of the pixels having a luminance value between the first magnetic susceptibility threshold value and the second magnetic susceptibility threshold value to be a weight value calculated according to a predetermined function connecting the first weight value and the second weight value.

5. The magnetic resonance imaging apparatus according to claim 3, wherein:

the threshold value determination part comprises;

a phase threshold value calculation part for determining one or more phase threshold values from pixel values of the phase image,

a phase histogram calculation part for calculating a phase histogram as a histogram of the pixel values of the phase image,

a magnetic susceptibility histogram calculation part for calculating a magnetic susceptibility histogram as a histogram of pixel values of the susceptibility map,

a histogram standard deviation calculation part for calculating standard deviations of the phase histogram and the magnetic susceptibility histogram, and

a magnetic susceptibility threshold value calculation part for calculating one or more of the magnetic susceptibility threshold values by using the phase threshold value or values, the standard deviation of the phase histogram, and the standard deviation of the magnetic susceptibility histogram.

6. The magnetic resonance imaging apparatus according to claim 1, wherein:

the weighting image is a phase mask image in which signal intensities of a negative phase region are reduced for a desired angle between a B₀ direction and an imaging slice direction.

7. The magnetic resonance imaging apparatus according to claim 6, wherein:

the weighting image generation part comprises;

a virtual magnetic field vector setting part for setting a vector of a direction different from the B₀ direction as a virtual magnetic field direction vector,

a pseudo-magnetic field distribution calculation part for calculating a pseudo magnetic field distribution as a pseudo-magnetic field distribution generated when a static magnetic field of the virtual magnetic field direction vector is virtually applied from the susceptibility map and the virtual magnetic field direction vector,

a pseudo-phase image calculation part for calculating a pseudo phase image as a pseudo-phase image from the pseudo-magnetic field distribution, and

a phase mask image calculation part for calculating a phase mask image in which phase difference is emphasized on the basis of luminance values of the pseudo-phase image.

8. The magnetic resonance imaging apparatus according to claim 1, wherein:

the image conversion part further comprises a phase image processing part for performing image processing for the phase image generated by the complex image conversion part.

9. A magnetic susceptibility-weighted image generation method for generating a magnetic susceptibility-weighted image in which magnetic susceptibility difference is emphasized from a complex image of which pixel values are complex numbers, which comprises:

a complex image conversion step of generating an absolute image and a phase image from absolute value components and phase components of the complex numbers of pixels of the complex image, respectively,

a magnetic field image generation step of generating a magnetic field image representing spatial distribution of magnetic field intensity from the phase image,

a susceptibility map generation step of generating a susceptibility map from the magnetic field image,

a weighting image generation step of generating a weighting image for performing weighting for enhancing contrast difference of a tissue of interest and a surrounding tissue from the susceptibility map, and

a magnetic susceptibility-weighted image generation step of generating a magnetic susceptibility-weighted image by multiplication of the absolute image and the weighting image.