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Computer simulation of irregular shaped lesions in radiographs

Facing an ever-increasing demand for diagnostic radiological examinations, the radiologist has turned to other means for assistance. In some cases this has been the utilization of trained technical assistants. New methods and techniques have been tested. In this learning process, simulated lesions can be useful in training of assistants. It can also be an integral part of the evaluation of their abilities to perform the required functions. Second, the study of radiographic images may be quantitatively explored as to their use in diagnosis. Previous radiographic simulations have made use of photographic and television simulations. However, greater quantitative control can be achieved by the utilization of the digital computer. This system provides a qualitative and quantitative control plus a high degree of flexibility throughout the system. Images and radiographs can be studied to determine the ability of the trained observer to perceive information as displayed in the traditional radiograph1. The purpose of this paper is to describe the system used to simulate lesions in the chest radiograms and the effect of shape on the detectability of these lesions.
 The general effect of contrast and lesion size must continue to be considered during the generation of the lesions. Various levels of contrast must be generated to test the Weber-Fechner law for complex images. Both sharp edges and Gaussian examples were used in determining the threshold of perception for each lesion. The background and immediate surrounding area were used to determine the contrast. The results were not unexpected. The useful lesion shape previously tested consisted of the nodular variety. This, however, is not the only lesion presented to the radiologist; therefore, this experiment concentrated on lesions developing in the bronchus and radiating outward.
 A series of lesions was generated at various contrast levels, shapes, and sizes. These were then shown to radiologists and their detection ability as a function of contrast and size was measured with a fixed viewing distance.