General Electric Cgr S.a.

General Electric Cge Sa

General Electric Cgt Sa

Dominique Cornuejols

Andrei Feldman

A method and a system for calibrating an x-ray scanner, in which the lengths d.sub.ij of x-ray paths are first computed by means of the image of the calibration standard. There are then computed both the theoretical attenuations Ac.sub.ij and the attenuations Am.sub.ij measured on the image. There are then deduced the coefficient of proportionality K between the values Ac.sub.ij and Am.sub.ij in order to obtain values of K.times.Ac.sub.i. The values KAc.sub.i and Am.sub.i are employed for calculating the corrections to be made per channel as a function of the attenuation.

Method and system for calibrating an x-ray scanner from the image of at

A method for elimination of parasitic noise in an x-ray scanner consists of computing the mean value of the signals of the ten first views in a circuit (26). This mean value is subtracted from the signals of the first view V.sub.1 in a circuit (27) so as to obtain the high-frequency components H.sub.1 which are considered as parasitic noise. The signals H.sub.1 are filtered in a high-pass filter before being subtracted from the signals of the view V.sub.1 to obtain signals V'.sub.1 which are free of parasitic components. The signals V'.sub.1 are processed in a sequential circuit (31) in order to obtain signals V'.sub.2 which are free of parasitic component. The same process is repeated for the signals of the other views V.sub.3 to V.sub.m.

Method for eliminating parasitic noise in an x-ray scanner

A method and system to calibrate an X-ray scanner uses a single circular phantom. The circular phantom is off-centered with respect to the axis of rotation of the scanner so as to introduce different paths in the phantom for each channel, depending on the angular positions of the scanner. This results in different attenuation measurements which are compared with values obtained by the computation of the path lengths which depend on the off-centered coordinates r and .PHI. and on the position of the scanner, thus enabling computation of the polynomial approximation coefficients to be applied to the measurements.

Method and system for the calibration of an x-ray scanner using an

The invention relates to x-ray scanners and more particularly to a method for calibrating scanners by means of a single standard of elliptical shape, for example. Attenuation measurements are performed with respect to a number of principal angular positions of the scanner about the standard. In addition, a number of meaurements or views are taken on each side of this principal position in order to compute a mean attenuation with respect to each channel. The attenuation curve is then smoothed by filtering and polynomial approximation.

Method and system for calibrating an x-ray scanner by employing a single

Disclosed is a method for the correction, in a scanner, of the defects due to the movements of the scanner. The method consists in having a rod which introduces a major attenuation and causing the scanner to make a full turn around a center of rotation O and obtaining m distinct views of the rod, each corresponding to an angular position .alpha..sub.j. The analysis of the signals of each view enables determining the angle .beta..sub.j of the rod. The knowledge of this angle .beta..sub.j leads to the computation of the coordinates b and c of the rod and the theoretical value .beta..sub.th of the angle .beta. for each view. The difference between the theoretical value .beta..sub.th and the measured value .beta..sub.j is used in the device for processing the scanner image.

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Palaiseau, France

Dominique Cornuejols