Electricity: measuring and testing – Particle precession resonance – Using a nuclear resonance spectrometer system
Reexamination Certificate
2001-01-09
2003-07-22
Hoff, Marc S. (Department: 2857)
Electricity: measuring and testing
Particle precession resonance
Using a nuclear resonance spectrometer system
C324S307000, C324S309000
Reexamination Certificate
active
06597172
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a water and fat separation image forming method, a magnetic resonance imaging apparatus, a reference peak phase detecting method and a reference peak position detecting method. More in details, the present invention relates to a water and fat separation image forming method and a magnetic resonance imaging apparatus capable of separately and preferably forming a water image and a fat image even in the case in which a plurality of independent signal regions are present in a complex number image taken by utilizing magnetic resonance. Further, the present invention relates to a reference peak phase detecting method and a reference peak position detecting method capable of simply detecting a phase or a position of a reference peak in a distribution satisfying a specific condition.
There is disclosed a water and fat separation image forming method for taking a complex number image by utilizing magnetic resonance to provide a phase difference between water and fat and separately forming a water image and a fat image from the complex number image by utilizing the phase difference between water and fat in, for example, “SMRM85vol. 1 pp. 172-173: Zvi Paltiel, Amir Ban (Elscient MRI Center)”.
FIG. 1
shows a flow of a conventional water and fat separation image forming method.
At step J
1
, an image is taken by utilizing magnetic resonance to provide a phase difference between water and fat and form a complex number image.
At step J
3
′, a phase error caused by a non-uniformity of a magnetic field is corrected.
At step J
5
′, a water image and fat image are separately formed by utilizing the phase difference between water and fat from the complex number image the phase of which has been corrected.
According to the conventional water and fat separation image forming method, as shown in
FIG. 2
, when there is only one signal region N in the complex number image (that is, when the signal region S is not divided by a noise region N), the water image and fat image can properly be formed to separate from each other.
However, when there are a plurality of signal regions S
1
through S
3
in the complex number image as shown by
FIG. 3
, (that is, the signal regions S
1
through S
3
are divided by a noise region N
2
), there poses a problem in which the water image and the fat image cannot properly be formed to separate from each other.
SUMMARY OF THE INVENTION
It is a first object of the present invention to provide a water and fat separation image forming method and a magnetic resonance imaging apparatus capable of separately and preferably forming a water image and a fat image even in the case in which there are present a plurality of independent signal regions in a complex number image taken by utilizing magnetic resonance.
Further, it is a second object of the present invention to provide a reference peak phase detecting method which is a method capable of being utilized in implementing the water and fat separation image forming method and the magnetic resonance imaging apparatus according to the first object and which can simply detect a phase of a reference peak in a distribution satisfying a specific condition.
Further, it is a third object of the present invention to provide a reference peak position detecting method which is a method generalizing the reference peak phase detecting method according to the second object and which can simply detect a position of a reference peak in a distribution satisfying a specific condition.
According to a first aspect of the present invention, there is provided a water and fat separation image forming method characterized in a water and fat separation image forming method for taking a complex number image by utilizing magnetic resonance to provide a phase difference between water and fat and separately forming a water image and a fat image from the complex number image by utilizing the phase difference between water and fat, wherein when there are present a plurality of independent signal regions in the complex number image, phases are respectively corrected in the respective signal regions, phase shifts among the respective signal regions are corrected, and then, the water image and the fat image are separately formed from the complex number image by utilizing the phase difference between water and fat.
When there are a plurality of signal regions in a complex number image, the reason that a water image and a fat image cannot properly be formed to separate is that phase shifts are present among the plurality of signal regions. That is, in one signal region, phase error caused by a non-uniformity in a magnetic field is continuous and therefore, phase of water in the signal region can be aligned by phase correction, further, phase of fat can also be aligned. Therefore, in the case of a single signal region, the water image and fat image can properly be formed to separate. However, when a signal region and another signal region are divided by a noise region, a phase error caused by a non-uniformity in a magnetic field in one signal region and a phase error caused by a non-uniformity in a magnetic field in other signal region, become discontinuous and therefore, although the phase of water can be aligned in the respective signal region, the phase of water cannot be aligned among the signal regions, further, although the phase of fat can be aligned in the respective signal region, the phase of fact cannot be aligned among the signal regions. Therefore, when there are a plurality of signal regions, the water image and the fat image cannot be properly formed to separate.
Hence, according to the first aspect of the water and fat separation image forming method, the phase correction is respectively carried out in the respective signal regions, thereafter, the phase shifts among the respective signal regions are corrected and thereafter, the water image and the fat image are separately formed by utilizing the phase difference between water and fat. By correction of the phase shift, the phase of water can be aligned in all of the signal regions, further, the phase of fat can also be aligned. Therefore, even when there are present the plurality of signal regions, the water image and the fat image can properly be formed to separate.
According to a second aspect of the present invention, there is provided the water and fat separation image forming method according to the first aspect, wherein in correcting the phase shifts, reference peak phases are respectively detected with respect to distributions of pixel numbers with regard to the phases of the respective signal regions subjected to the phase correction and the distributions of the pixel numbers with regard to the phases of the respective signal regions are shifted such that the reference peak phases coincide with each other.
Taking a distribution of a pixel number with respect to a phase in a respective signal region subjected to phase correction, the pixel number becomes a peak at a phase of water and a phase of fat.
Therefore, according to a second aspect of the water and fat separation image forming method, for example, as reference peak phases, phases of peaks of water are detected and distributions of the pixel numbers with respect to the phases of the respective signal regions are shifted such that the peak phases of water in the respective signal regions coincide with each other. Thereby, the phase of water can be aligned in all of the signal regions, further, the phase of fat can also be aligned. Therefore, even when there are present the plurality of signal regions, the water image and the fat image can properly be formed to separated.
According to a third aspect of the present invention, there is provided a magnetic resonance imaging apparatus characterized in comprising imaging means for taking a complex number image by utilizing magnetic resonance to provide a phase difference between water and fat, phase correcting means for respectively carrying out phase correction in respective signal regions when there are present
GE Medical Systems Global Technology Company LLC
Hoff Marc S.
Kim Paul L
Kojima Moonray
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