[Factors of image quality in spiral x-ray computed tomography].

In helical CT, there are 4 mains factors of quality: The in-plane spatial resolution that is the same in conventional CT; The spatial resolution 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 increase factor can be easily calculated; The signal to noise ratio which depends on the collimation, the mA, the KV and the reconstruction algorithm. The signal to noise ratio is not depending on the table speed; The reconstruction interval which can be less than the slice thickness. Then the contrast of small lesion is improved and stair-step artifacts are reduced in 3D reformations.