Influence of gantry angle in helical computed tomography. Unsharpness of vertical direction

When we let gantry tilt and do scan in helical CT, sharpness deteriorates. The cause, vertical relation collapses between movement direction and a reconstructed plane. In this study, we were able to identify that unsharpness had directivity by MTF which used LSF this time to vertical direction of a reconstructed image. And we were able to let precision of experiment improve by revising it by data of conventional scan which didn't receive influence in gantry tilt. (author)