Image analysis – Histogram processing – For setting a threshold
Patent
1990-04-17
1991-11-12
Moore, David K.
Image analysis
Histogram processing
For setting a threshold
36441314, 36441317, 36441319, G06K 900
Patent
active
050654365
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to removement of artifacts in a reconstructed image in an X-ray computerized tomograph which extracts data corresponding to transmitted data of a parallel beam X-ray from transmitted data of an X-ray acquired based on a fan beam X-ray and reconstructs an image based on the data.
BACKGROUND ART
An X-ray computerized tomograph (hereinafter, called as an X-ray CT) is a device which reconstructs a tomogram image of a body under test from transmitted data of an X-ray obtained by irradiating an X-ray from the circumference of a body under test. An X-ray CT of a ROTATE - ROTATE system irradiates a fan beam X-ray on a body under test and detects the strength of an X-ray which transmits the body under test by use of a multi-channel X-ray detector. Accordingly, view data obtained by one irradiation become fan beam data. As one of methods of reconstructing an image based on such the view data, there is known a method in which parallel beam data are extracted from fan beam data, and an image reconstructing algorithm for a parallel beam is applied to the parallel beam data. In that case, data based on beams which are parallel with each other are picked up from fan beam data having different views with each other, thereby forming parallel beam data for each view. Therefore, data in each channel in one view have the time of irradiation of an X-ray which is different for each channel. Accordingly, in the case where an X-ray source generates, for example, a ripple-shaped output variation, data for one view include influences of such the X-ray output variation in the channel direction. The influences of such the X-ray output variation can be removed by carrying out acquisition of data in the reference channel of an X-ray detector with a sufficiently fine sampling period and carrying out correction of view data using the data in the reference channel. But, this is not effective in the case where an X-ray output decreases instantaneously due to an abnormal discharge occurring in an X-ray tube and so forth, and shower-shaped artifacts occur on the reconstructed image due to the influence of the above-mentioned decrease of the output.
SUMMARY OF THE INVENTION
It is an object of the present invention to remove shower-shaped artifacts generated in a reconstructed image due to influences of an instantaneous change in strength of an X-ray in an X-ray CT which extracts data corresponding to transmitted data of a parallel beam X-ray from transmitted data of an X-ray acquired based on a fan beam X-ray and reconstructs an image based on the data.
The present invention is characterized in that data corresponding to a plurality of views among output data of a data acquisition device are stored in a buffer memory, view data in which the influences of a variation in strength of an X-ray have been removed are formed by weighted averaging the data corresponding to a plurality of views stored in the buffer memory, and view data at the time when a variation in strength of an X-ray was present ar replaced with the view data.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a conceptual constitution diagram of an embodiment according to the present invention; and
FIGS. 2a and b are diagrams explanatory of correction of data using an embodiment according to the present invention.
BEST MODE FOR CARRYING OUT THE INVENTION
In FIG. 1, reference numeral 1 is a multi-channel X-ray detector for detecting a fan beam X-ray which is irradiated from an X-ray tube (not shown) to transmit a body under test (not shown) and outputting a signal proportional to strength of a X-ray, and 2 is a data acquisition device which converts output signals of the multi-channel of the X-ray detector 1 into a digital signal and then acquires them. The X-ray detector 1 and the data acquisition device 2 are both same as those usually used in an X-ray CT. Reference numeral 3 is a correction device which forms a feature of the present invention and includes a buffer memory 4 and a weighted averaging circuit 5. Output data corr
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patent: 4707786 (1987-11-01), Dehner
patent: 4731865 (1988-03-01), Sievenpiper
patent: 4903205 (1990-02-01), Hishinuma
patent: 4903310 (1990-02-01), Takeo et al.
patent: 4947323 (1990-08-01), Smith
patent: 4975970 (1990-12-01), Zettel et al.
Kojima Moonray
Mancuso Joseph
Moore David K.
Yokogawa Medical Systems Limited
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