SPIRAL CT - IMAGE QUALITY CONSIDERATIONS

In helical CT, there are 4 mains factors of quality: The in-plane spat ial resolution that is the same in conventional CT; The spatial resolu tion on the Z axis, which is the slice thickness. The increase factor of the slice thickness between a conventional and a helical CT depends on the pitch and the reconstruction algorithm. The value of the incre ase factor can be easily calculated; The signal to noise ratio which d epends on the collimation, the mA, the KV and the reconstruction algor ithm. The signal to noise ratio is not depending on the table speed; T he reconstruction interval which can be less than the slice thickness. Then the contrast of small lesion is improved and stair-step artifact s are reduced in 3D reformations.