Forensic considerations for preprocessing effects on clinical MDCT scans

Manipulation of digital photographs destined for medico-legal inquiry must be thoroughly documented and presented with explanation of any manipulations. Unlike digital photography, computed tomography (CT) data must pass through an additional step before viewing. Reconstruction of raw data involves reconstruction algorithms to preprocess the raw information into display data. Preprocessing of raw data, although it occurs at the source, alters the images and must be accounted for in the same way as postprocessing. Repeated CT scans of a gunshot wound phantom were made using the Toshiba Aquilion 64-slice multidetector CT scanner. The appearance of fragments, high-density inclusion artifacts, and soft tissue were assessed. Preprocessing with different algorithms results in substantial differences in image output. It is important to appreciate that preprocessing affects the image, that it does so differently in the presence of high-density inclusions, and that preprocessing algorithms and scanning parameters may be used to overcome the resulting artifacts.