X-ray sensors are available both as line sensors and area sensors. From a purely geometric standpoint, line sensors would be perfect. Synchronized movement of the X-ray source and the line sensor relative to the measured object in the direction of the rotary axis can ensure that the section plane through the object is always perpendicular to the rotary axis. The disadvantage of this fan beam tomography is that each section plane needs to be captured individually in every rotary position. Compared to using an area sensor with, for example, 1000 lines, this would require 1000 times the measurement time if all other parameters are equal. The energy of the X-ray source is utilized much less efficiently, because only a single fan of the beam cone is used. For this reason, area sensors that capture several section planes of the measured object at once, according to the number of lines on the sensor, are typically used. The disadvantage of this cone beam tomography with circular motion, however, is that the captured object section planes, except for the center one, are not perpendicular to the rotary axis. This causes fundamental measurement errors during the mathematical reconstruction of the volume data from the 2D radiographic images. Depending on the precision requirements, these must be corrected.

As seen in image above:  Tomography using a line sensor (a) and an area sensor (b)