An improved image algorithm for CT scanners

A common artifact in CT head-section images is a cupping or broad "whitening" effect near the skull which is due at least in part to the polychromaticity of the x-ray beam. In this paper, a general method is presented for removing this artifact empirically by a combination of two approaches. The gross cupping is removed by modifying the raw transmission data prior to reconstruction. The residual whitening near the bone is removed conveniently by modifying the reconstruction filter function. Examples of the modifications are shown using the AS&E CT scanner. The method convolves or deconvolves the CT image with an appropriate point spread function. Since the filter-function modifications are done conceptually in real space rather than in frequency space, the details of the modifications are more easily understood.