Using spiral (better helical) tomography, the cone beam artifacts that arise in conventional cone beam tomography can be prevented.  This works by moving the measured object along the rotary axis as it rotates.  In spiral tomography, each layer of the object is captured by at least one X-ray image in the central plane of the cone beam.  This is the plane perpendicular to the rotary axis at the focal spot.  With appropriate mathematical reconstruction methods, known as exact reconstruction, the volume can be calculated with significantly better accuracy.  Linear axes are used for spiral tomography such as are also used for raster tomography in the direction of the rotary axis.  The drawback of the method is the long measurement time.