This is a preclinical (cone beam) computed tomography (CT) dataset containing the raw projection images of a NEMA image quality phantom measured with the preclinical Siemens Inveon CT scanner. Included are the projection images (.cat), the corresponding header that contains the relevant scanner information as well as FDK reconstruction (.img), created by the Siemens Inveon Acquisition workplace software, and its header. This dataset was used for attenuation correction of PET data. The projection data first contains an unknown header section of 25280 bytes. After this, a dark measurement of size 768x512 is included and after the dark data is 768x512 light measurement. These can be used for dark/light normalization/flat-field correction. After these, the actual projection images are included. This is also a step-and-shoot measurement with three different bed positions. The data is formatted as signed 16-bit integers and contains 121 projections for each bed position. The projection data contains the raw detected photons. The center of rotation is not in the origin and without corrections will cause artifacts in the reconstructions. The header file contains variables ct_projection_center_offset and ct_projection_horizontal_bed_offset that can be used to correct for the offset. If you shift the source location with ct_projection_center_offset - ct_projection_horizontal_bed_offset the reconstructions should be artifact free. Note, however, that this was determined experimentally and may not be totally accurate. An example utilizing this dataset is available with the OMEGA software. A PET measurement of the same phantom is available from https://zenodo.org/record/4646897. The measurement data was collected by Jarmo Teuho.