X-ray or gamma ray systems or devices – Specific application – Computerized tomography
Patent
1994-11-09
1996-12-31
Porta, David P.
X-ray or gamma ray systems or devices
Specific application
Computerized tomography
378 5, 378901, 36441315, A61B 603
Patent
active
055901654
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a method for generating a fat distribution image by a CT system. More particularly, the present invention relates to a method for generating a fat distribution image by a CT system, wherein an image of fat distribution is generated from a cross sectional image data via X ray.
BACKGROUND ART
As the method for generating a fat distribution image from a cross sectional image data via X ray, a method is known comprising determining a threshold value so as to extract the CT number range from -130 to -100 from the cross sectional image data, based on the finding that the CT number of fat is about -130 to -100.
However, because the fat composition ratio in human bodies varies depending on the tissue, the conventional method described above comprising determining a threshold value has problems in that fat cannot be separated solely from other components in tissues and in that the fat composition ratio in ROI (region of interest) cannot be determined.
DISCLOSURE OF INVENTION
Thus, the object of the present invention resides in providing a method for generating a fat distribution image by a CT system, wherein an image representing fat distribution is generated, based on the fat composition ratio in a tissue.
In a first aspect of the present invention, the method for generating a fat distribution image by a CT system wherein an image of fat distribution is generated from a cross sectional image data via X ray comprises the steps of a scanning step wherein scanning is effected at least at two different levels of X-ray tube voltage using a phantom containing a sample rod of a fat standard material in addition to plural sample rods with different densities of a bone mineral equivalent material to generate at least two cross sectional image data, a CT number detecting step wherein the CT number of each pixel in the whole region or an objective region of the cross sectional image data is detected as the "CT number of a tissue including fat", ie. .alpha.wf, a linear regression calculating step wherein the CT number of the bone mineral equivalent material is detected in the cross sectional image data following the principle of quantitative measurement of bone mineral mass to calculate a linear regression between the CT number and the density of the bone mineral equivalent material and to define the CT number as the "CT number of a tissue excluding fat", ie. .alpha.nf, a fat standard material CT number detecting step wherein the "CT number of the fat standard material", ie. .alpha.ff is detected in the cross sectional image data, a soft tissue standard material CT number detecting step wherein the CT number of blood in the cross sectional image data is detected as the "CT number of a soft tissue standard material", ie. .alpha.st, a CT number application step wherein ".alpha." in the equation .alpha.=.alpha.wf-.alpha.nf is defined as the variation of the CT number due to fat while ".beta." in the equation .alpha.=.beta..multidot.{.alpha.ff-.alpha.st} is defined as a fat ratio parameter and the "CT number of a tissue including fat" ie. .alpha.wf, etc., should be applied to the equation mineral equivalent material and the "CT number of a tissue excluding fat", ie. .alpha.nf should be deleted in at least two linear regressions calculated at the linear regression calculating step and in at least two equations (A) to be applied at the CT number application step, to calculate the fat ratio parameter .beta. on the basis of the detected CT number of each pixel at the CT number detecting step, and a fat ratio parameter image generation step wherein an image is generated on the basis of the calculated fat ratio parameter .beta..
According to the method for generating a fat distribution image by a CT system of the present invention, scanning is effected at least at two different levels of X-ray tube voltage at the scanning step, using a phantom containing a sample rod of a fat standard material in addition to plural sample rods with different densities of a bone mineral equivalent
REFERENCES:
patent: 4922915 (1990-05-01), Arnold et al.
patent: 4985906 (1991-01-01), Arnold
patent: 5222021 (1993-06-01), Feldman et al.
Gohno Makoto
Horiuchi Tetsuya
Bruce David Vernon
GE Yokogawa Medical Systems Limited
Kojima Moonray
Porta David P.
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