Distortion correction method for linear scanning X-ray system

1. A method of operating imaging apparatus of the kind having a radiation source and an associated radiation detector which are moveable relative to a subject, the method comprising:

(a) generating a divergent imaging beam from the radiation source;

(b) moving the radiation source and the radiation detector relative to a subject in a scanning direction to generate output signals from the detector, thereby generating image data containing distortion in a direction transverse to the scanning direction;

(c) changing the orientation of the radiation source in a direction transverse to the scanning direction and repeating step (b) one or more times to generate a plurality of sets of image data;

(d) processing each set of image data to obtain equivalent parallel imaging beam data therefrom, corresponding to a given angle in the divergent imaging beam; and

(e) combining a plurality of said equivalent parallel imaging beam data to generate a synthesized parallel imaging beam image.

2. The method of claim 1 wherein the divergent imaging beam is a fan shaped imaging beam generated by a linear scanning apparatus.

3. The method of claim 2 wherein the fan shaped imaging beam is relatively narrow in the scanning direction and relatively wide in a direction transverse to the scanning direction.

4. The method of claim 2 wherein changing the orientation of the radiation source in a direction transverse to the scanning direction comprises rotating the radiation source and detector about an axis extending parallel to the scanning direction at selected angular intervals.

5. The method of claim 4 wherein the linear scanning apparatus comprises a support member which supports the radiation source and the associated radiation detector for rotation about an axis which extends parallel to the scanning direction, but which is offset relative to a midline of the fan shaped imaging beam, the method including the step of processing the image data to re-project the image data so that it represents a virtual fan shaped imaging beam having a midline that coincides with the axis of rotation of the support member.

6. The method of claim 5 wherein the image data defines a multi-line image, the method comprising generating a set of sinograms from the image data, each sinogram representing angular views at a specified line of the image, reprojecting the sinogram data from a fan bean to a parallel beam format, constructing a set of new sinograms consisting of virtual parallel beam data, and reconstructing a virtual parallel beam image from the virtual parallel beam data at a selected angle of view.

7. Imaging apparatus comprising:

(a) a radiation source arranged to generate a divergent imaging beam and an associated radiation detector;

(b) a first drive arranged to move the radiation source and the detector relative to a subject in a scanning direction to generate output signals from the detector, thereby performing a scan generating image data containing distortion in a direction transverse to the scanning direction;

(c) a second drive arranged to change the orientation of the radiation source in a direction transverse to the scanning direction incrementally between repeated scans, thereby to generate a plurality of sets of image data;

(d) at least one processor for processing each set of image data to obtain equivalent parallel imaging beam data therefrom, corresponding to a given angle in the divergent imaging beam, and for combining a plurality of said equivalent parallel imaging beam data to generate a synthesized parallel imaging beam image; and

(e) a display for generating a visual display of the synthesized parallel imaging beam image.

8. Imaging apparatus according to claim 7 which is a linear scanning apparatus in which the first drive is arranged to move the radiation source and the associated radiation detector along a linear path corresponding to the scanning direction, and wherein the divergent imaging beam is a fan shaped imaging beam.

9. Imaging apparatus according to claim 8 wherein the fan shaped imaging beam is relatively narrow in the scanning direction and relatively wide in a direction transverse to the scanning direction.

10. Imaging apparatus according to claim 8 wherein the second drive is arranged to change the orientation of the radiation source in a direction transverse to the scanning direction by rotating the radiation source and detector about an axis extending parallel to the scanning direction at selected angular intervals.

11. Imaging apparatus according to claim 10 wherein the linear scanning apparatus comprises a support member which supports the radiation source and the associated radiation detector for rotation about an axis which extends parallel to the scanning direction, but which is offset relative to a midline of the fan shaped imaging beam, said at least one processor being operable to apply an algorithm to the image data to re-project the image data so that it represents a virtual fan shaped imaging beam having a midline that coincides with the axis of rotation of the support member.

12. Imaging apparatus according to claim 11 wherein the image data defines a multi-line image, said at least one processor being operable to generate a set of sinograms from the image data, each sinogram representing angular views at a specified line of the image; to reproject the sinogram data from a fan bean to a parallel beam format; to construct a set of new sinograms consisting of virtual parallel beam data; and to reconstruct a virtual parallel beam image from the virtual parallel beam data at a selected angle of view.