  Computed tomography (CT) is a well-established method for non-destructive
testing (NDT), typically performed with X-radiation. Here, an alternative
approach for CT based on THz radiation is presented. Optimized for the
potential use-case of NDT on extruded plastic profiles, an imaging model and
different resultant reconstruction approaches are derived. For experimental
validation, 3D printed plastic profiles were tested with a THz time-domain
spectrometer in transmission geometry. On the basis of differently complex
samples, it is shown that the derived reconstruction approaches are highly
robust. Quantitative analysis has further shown that the results are highly
accurate for samples without curved structures.
