Electricity: measuring and testing – Particle precession resonance – Using a nuclear resonance spectrometer system
Reexamination Certificate
2003-10-06
2004-08-10
Arana, Louis (Department: 2859)
Electricity: measuring and testing
Particle precession resonance
Using a nuclear resonance spectrometer system
C324S306000
Reexamination Certificate
active
06774630
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of Japanese Application No. 2002-297076 filed Oct. 10, 2002.
BACKGROUND OF THE INVENTION
The present invention relates to an MR (magnetic resonance) image producing method and an MRI (magnetic resonance imaging) apparatus, and more particularly to an MR image producing method and MRI apparatus that improve on rendering capability for a blood vessel.
A conventional MRI apparatus comprises MR signal acquiring means for acquiring MR signals, window-processing means for window-processing the MR signals using a window function that has a value of “one” from the center of a k-space to a position near the periphery of the k-space and has a decreasing value as it goes closer to the periphery, and Fourier-transformation processing means for conducting Fourier-transformation processing on the window-processed MR signals to produce an MR image.
The window processing is conducted to concentrically suppress a high frequency portion of MR signals to thereby prevent truncation artifacts or anisotropic noise texture due to signal acquisition confined to a limited rectangular region in a k-space by the MRI apparatus.
Related conventional techniques are disclosed in Japanese Patent Application Laid Open Nos. H4-53531 and H6-121781.
In the conventional MRI apparatus, the same window processing is conducted whether the image to be produced is a blood flow image or not.
In other words, the conventional window processing is not optimal when the image to be produced is a blood flow image, and it cannot improve rendering capability for a blood vessel.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an MR image producing method and MRI apparatus that improve on rendering capability for a blood vessel by optimizing window processing when an image to be produced is a blood flow image.
In a first aspect, the present invention provides an MR image producing method characterized in comprising: window-processing MR signals using a window function that has a value less than one at a center and in its proximate region in a k-space and on a periphery and in its proximate region in the k-space, and, between the regions in which the window function has a value less than one, has a value larger than that in the regions in which the window function has a value less than one; and applying Fourier-transformation processing to the window-processed MR signals to obtain an MR image.
In this configuration, the proximate region of the center of the k-space is a range of about five—twenty data points from the center of the k-space. The proximate region of the periphery of the k-space is a range of about five—twenty data points from the periphery of the k-space.
According to the MR image producing method of the first aspect, since a window function that has a value less than one at a center and in its proximate region in the k-space is employed, MR signals near the center of the k-space are suppressed. MR signals of a tissue portion are narrowly distributed near the center of the k-space, while MR signals of a blood flow portion are broadly distributed in a high frequency region, as well as near the center. Thus, the MR signals of the tissue portion are strongly suppressed, while the MR signals of the blood flow portion are relatively weakly suppressed. Therefore, rendering capability for a blood vessel is relatively improved.
Moreover, since the window function has a value less than one on a periphery and in its proximate region in the k-space, a high frequency portion of MR signals can be concentrically suppressed as in the conventional technique.
In a second aspect, the present invention provides an MR image producing method characterized in comprising: window-processing MR signals using a window function that has a value less than one at a center of a k-space, first increases to a value C equal to or more than one as it goes farther from the center, remains at C for a certain duration, then passes to one, and decreases to a value less than one as it goes from near a periphery to the periphery of the k-space; and applying Fourier-transformation processing to the window-processed MR signals to obtain an MR image.
In this configuration, the region in which the window function has a value increasing to a value C from the center of the k-space is a range of about three—fifteen data points from the center of the k-space. The region in which the window function remains at C for a certain duration is a range of about twenty—fifty data points. The region in which the window function passes from C to one is a range of about three—ten data points. The region in which the window function has a value less than one is a range of about five—twenty data points from the periphery of the k-space.
According to the MR image producing method of the second aspect, since the window function has a value less than one at a center and in its proximate region in the k-space, MR signals near the center of the k-space are suppressed. MR signals of a tissue portion are narrowly distributed near the center of the k-space, while MR signals of a blood flow portion are broadly distributed in a high frequency region, as well as near the center. Thus, the MR signals of the tissue portion are strongly suppressed, while the MR signals of the blood flow portion are relatively weakly suppressed. Next, in the region in which “the window function remains at C for a certain duration”, a zero-th order peak portion (a crest having a maximum value at the center) in the MR signals of the blood flow portion is preserved or amplified. Next, in the region in which “the window function passes to one”, a first- or higher order peak portion (a crest having a maximum value at a position except the center) in the MR signals of the blood flow portion is preserved. Thus, rendering capability for a blood vessel is relatively improved.
Moreover, since the window function has a value less than one on a periphery and in its proximate region in the k-space, a high frequency portion of MR signals can be concentrically suppressed as in the conventional technique.
In a third aspect, the present invention provides the MR image producing method having the aforementioned configuration, characterized in that: the window function is a function using a Gaussian function in the region in which the window function increases to C.
According to the MR image producing method of the third aspect, a Gaussian function exp{−|k|
2
/a
2
} can be used to smoothly increase the value from a value less than one to a value C.
In a fourth aspect, the present invention provides the MR image producing method having the aforementioned configuration, characterized in that: the window function is a function using a Fermi-Dirac function in the region in which the window function decreases to a value less than one.
According to the MR image producing method of the fourth aspect, a Fermi-Dirac function 1/(1+exp{(|k|−R)/b}) can be used to smoothly reduce the value from one to a value less than one.
In a fifth aspect, the present invention provides an MR image producing method characterized in comprising: window-processing MR signals using a window function that has a value less than one at a center of a k-space, first increases to one as it goes farther from the center, remains at one for a certain duration, and decreases to a value less than one as it goes from near a periphery to the periphery of the k-space; and applying Fourier-transformation processing to the window-processed MR signals to obtain an MR image.
According to the MR image producing method of the fifth aspect, since the window function has a value less than one at a center and in its proximate region in the k-space, MR signals near the center of the k-space are suppressed. MR signals of a tissue portion are narrowly distributed near the center of the k-space, while MR signals of a blood flow portion are broadly distributed in a high frequency region, as well as near the
Arana Louis
Armstrong Teasdale LLP
GE Medical Systems Global Technology Company LLC
Horton Esq. Carl B.
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