As conventional radiation tomographic image generating apparatus, there are an X-ray tomographic apparatus which is capable of tomosynthesis, and an X-ray CT apparatus (see Patent Document 1, for example). Such a conventional apparatus has an X-ray tube for emitting X-rays toward an inspection object, an X-ray detector disposed opposite this X-ray tube for detecting X-rays transmitted through the inspection object, and an X-ray tomographic image generating device for generating X-ray (radiation) tomographic images (hereinafter called “tomographic images” as appropriate) from projection data (projection images) acquired by the X-ray detector.
The conventional apparatus, while moving the X-ray tube and the X-ray detector in an integrated or interlocked manner, acquires projection data by carrying out X-raying from a plurality of directions with respect to the inspection object. Tomographic images are acquired by operating the X-ray tomographic image generating device to carry out image reconstruction of the acquired projection data for a plurality of frames. Tomosynthesis is a technique for generating tomographic images of an arbitrary cutting height by collecting projection data for a plurality of frames through one tomographic operation, and by image reconstruction of the projection data for a plurality of frames.
Conventionally, when a high X-ray (radiation) absorber (hereinafter called “high absorber” as appropriate) in form of a metal, for example, is present in the inspection object, artifacts will appear in the tomographic images generated by carrying out image reconstruction since X-rays are shielded by the high absorber. So various methods for reducing the artifacts due to high absorbers have been proposed. In Patent Document 1, for example, a final tomographic image is acquired by the method of the flow chart shown in FIG. 14.
That is, actual measurement projection data is acquired first (step S101). A high absorber area is identified from the actual measurement projection data (step S102). Data replacement is carried out for the high absorber area of the actual measurement projection data with pixels adjacent the high absorber area (step S103). Image reconstruction is done from projection data resulting from the data replacement, to generate a first reconstruction image (step S104). Forward projection data is created by projecting the first reconstruction image forward (step S105). The forward projection data is adjusted, and the adjusted forward projection data is put to image reconstruction to generate a second reconstruction image (step S106). And a final tomographic image (reconstruction image) is acquired by carrying out the forward projection, adjustment and image reconstruction once or a plurality of times iteratively.
As described above, the conventional method obtains a tomographic image by erasing, through replacement, a high absorber area reflected in each of the actual measurement projection data, and reconstructing these. This acquires tomographic images which have reconstructed tissue around the high absorber with high accuracy, and have also reduced the artifacts around the high absorber. The conventional apparatus has a process for identifying the high absorber area reflected in the actual measurement projection data.