In a CT scanner, the cross-sectional image is reconstructed from:
Computed tomography employs a rotating gantry containing X-ray tube and opposite detector array. As tube circles patient, numerous fan-shaped X-ray projections traverse head from many angles, attenuated differentially by bone, soft tissue, blood and cerebrospinal fluid according to electron density and atomic number. Detectors measure remaining intensity, generating attenuation profiles. Filtered back-projection or iterative algorithms mathematically reconstruct these one-dimensional projections into two-dimensional axial cross-sectional images. Thus image contrast originates entirely from X-ray absorption, not laser beams, magnetic spin excitation or ultrasound echo reflection for anatomical formation.
Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.