Complex sentence: In the past, CT was limited to acquiring images in the axial plane (or near axial), and so were called Computed "Axial" Tomography scans (CAT scans).
Split into simpler sentences: In the past, CT was limited to acquiring images in the axial plane (or near axial). The scans used to be called Computed "Axial" Tomography scans (CAT scans).