Image processing of conventional tomograms.

Previous authors have suggested that high pass spatial filtering of axial transverse and circular tomograms would improve the perceived image. A preliminary study here shows that good signal-to-noise ratio is critical for the success of image processing for the contrasts obtainable in the clinical situation. The successful image processing of a small object on the Philips Polytome is demonstrated, as well as a clinical example. A similar trial with the Toshiba axial transverse tomography machine was not successful due to lower subject contrast with higher kVp techniques. A derivation of the optical transfer function of circular and axial transverse tomograms is given, with emphasis on those features that image processing can improve. To accomplish image processing, two methods employing incoherent light were investigated. Either method may be regarded as an analogue equivalent to the mathematical operations employed by digital computers in the reconstruction of CT images. First, a simple all-purpose image processor is described that makes use of the Herschel effect. Second, a simple film copying technique that simulates a high pass spatial filter is introduced and used to improve tomographic images.