X-ray or gamma ray systems or devices – Specific application – Computerized tomography
Reexamination Certificate
2002-03-26
2003-04-01
Bruce, David V. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Computerized tomography
C378S008000, C378S901000
Reexamination Certificate
active
06542571
ABSTRACT:
The present invention relates to a method of reducing artifacts in object images acquired by means of measurement signals sent by a source through the object onto a detector, which method comprises the steps of: a) adaptively filtering the data signals received by the detector in dependence of the data value; b) processing the data signals to indicate the attenuation of the measurement signals passing through the object; and c) reconstructing an image of the object based on the filtered and processed data signals.
The invention also relates to a computed tomography device.
A method and a computed tomography device of this kind are known from U.S. Pat. No. 5,416,815.
The known computed tomography device includes an X-ray source and an X-ray detector which can rotate together about the object to be examined, notably a patient. Using the known method, the known computed tomography device acquires a plurality of cross-sectional images of the object along mutually parallel planes having a predetermined orientation. The cross-sectional images are acquired notably along a number of mutually parallel planes. This is achieved by rotating the X-ray source and the X-ray detector about the object while displacing the object and the X-ray detector and the X-ray source relative to one another. It is thus achieved that a cross-sectional image is acquired each time along the plane in which the X-ray detector and the X-ray source rotate about the object. Subsequently, the X-ray source with the X-ray detector and the object are displaced relative to one another, so that the plane in which the X-ray source and the X-ray detector rotate about the object is shifted and a next cross-sectional image is acquired. The cross-sectional images relate to a (sub)volume of the object.
According to the known method first the data signals are processed to indicate the attenuation of the measurement signals passing through the object. Usually this step involves a log adjustment by taking the negative logarithm of the data signals. Next the data signals received by the detector are adaptively filtered in dependence of the data signal value.
The known method has the drawback that very small data signals thereby introduce errors known as streak artifacts leading to so called “frozen noise”.
It is an object of the invention to provide a method and a computed tomography device of the kind as described in the preamble in which streak artifacts are greatly reduced.
The method according to the invention is characterized in that step b) is performed on the adaptively filtered data resulting from step a).
The computed tomography device according to the invention comprises a processing unit for carrying out the method according to the invention.
The invention further refers to a computer program for carrying out the method according to the invention.
REFERENCES:
patent: 5416815 (1995-05-01), Hsieh
patent: 5818896 (1998-10-01), Hsieh
patent: 6044125 (2000-03-01), Flohr et al.
patent: 6215841 (2001-04-01), Hsieh
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