Method and system for calibrating an x-ray scanner from the image of at least one calibration standard

Claim 3

A method of calibration according to claim 1, wherein at least some of the operations are repeated for other calibration standards having different diameters.

Claim 4

A method of calibration according to claim 1, wherein the step of computing the coefficient of proportionality K includes a first step of computing the mean of the values of both Ac i and Ami corresponding to a the ith channel, a second step of comparing the mean values thus obtained so as to obtain one coefficient of proportionality K i per channel and a third step of computing the mean value of the coefficients K i , K being the mean value of the coefficients K.

Claim 5

An x-ray scanner system, comprising: an x-radiation source, a N-channel detection device for detecting x-rays from said x-radiation source, a calibration standard interposed between the x-ray radiation source and the N-channel detection device, means for producing a measured attenuation matrix Ac ij , wherein i=1 to N, and i corresponds to the ith channel of the N channels of the detector, j=1 to m, and j corresponds to the jth view of m views of the calibration, said measured attenuation matrix containing x-ray attenuation values due to transmission of x-rays through the calibration standard, first computing means for calculating, from the attenuation matrix of the calibration standard, N=m lengths d ij of x-ray paths through the standard, means for determining a theoretical attenuation matrix Am ij corresponding to theoretical attenuation of x-rays passing through the calibration standard based upon the position, shape and density of the standard, and a model of x-ray attenuation, for m views and N channels, second computing means for calculating a coefficient of proportionality K between the values Ac ij and Am ij , by summing both Ac ij and Am ij over i and j and setting K equal to a ratio of the sums, recording means for recording the values K×Ac i and the values Am i , wherein Ac i and Am i are the means values corresponding to the m views for each of the i detectors, third computing means for calculating, from the values K ×Ac i and Am i , corrections to be applied to each channel as a function of the attenuation, and means for calibrating the x-ray scanner system using the corrections calculated from K×Ac i and Am i .

Claim 6

An x-ray scanner system, comprising: an x-radiation source, a N-channel detection device for detecting x-rays from said x-radiation source, a calibration standard interposed between the x-ray radiation source and the N-channel detection device, means for producing a measured attenuation matrix Ac ij , wherein i=1 to N, and i corresponds to the ith channel of the N channels of the detector, j=1 to m, and j corresponds to the jth view of m views of the calibration, said measured attenuation matrix containing x-ray attenuation values due to transmission of x-rays through the calibration standard, first computing means for calculating, from the attenuation matrix of the calibration standard, N=m lengths d ij of x-ray paths through the standard, means for determining a theoretical attenuation matrix Am ij corresponding to theoretical attenuation of x-rays passing through the calibration standard based upon the position, shape and density of the standard, and a model of x-ray attenuation, for m views and N channels, second computing means for calculating a coefficient of proportionality K between the values Ac ij and Am ij , by summing both Ac ij and Am ij over i and j and setting K equal to a ratio of the sums, recording means for recording the values K×Ac i and the values Am i , wherein Ac i and Am i are the means values corresponding to the m views for each of the i detectors, third computing means for calculating, from the values K ×Ac i and Am i , corrections to be applied to each channel as a function of the attenuation, and means for calibrating the x-ray scanner system using the corrections calculated from K×Ac i and Am i .

Claim 9

A method according to claim 5, wherein said step (A) comprises (i) collecting reference data for each channel using said source of x-radiation and said detection device, then (ii) positioning said first calibration standard between said source of x-radiation and said detection device, then (iii) collecting calibration data for each channel, using said source of x-radiation and said detection device, and then (iv) combining said reference data with said calibration data to obtain said x-ray attenuation data.

Claim 10

A method according to claim 6, further comprising repeating said steps (A) through (D) for a second calibration standard prior to said step (E), said second calibration standard having a diameter which is different than that of said first calibration standard.

Claim 11

A method according to claim 5, further comprising revolving said scanner around said calibration standard and obtaining a plurality of views, and wherein said step (A) comprises collecting x-ray attenuation data for each of said views.

Claim 12

A method according to claim 5, further comprising the step of displaying an image of said calibration standard.

Claim 13

A method according to claim 5, wherein said step (B) comprises computing said theoretical attenuations based upon the position, shape, and density of said first calibration standard.

Claim 16

An apparatus according to claim 11, wherein said means (i) comprises (1) means for collecting reference data for each channel using said source of x-radiation and said detection device, (2) means for positioning said first calibration standard between said source of x-radiation and said detection device, (3) means for collecting calibration data for each channel using said source of x-radiation and said detection device, and (4) means for combining said reference data with said calibration data to obtain said x-ray attenuation data.

Claim 17

An apparatus according to claim 11, further comprising a display device which displays an image of said calibration standard.

Claim 18

An apparatus according to claim 11, wherein said means (ii) comprises means for computing said theoretical attenuations based upon the position, shape, and density of said first calibration standard.