This paper addresses the hypothesis that artificially implanted lung nodules from computed tomography exams (CT exams) into chest radiographs can improve the performance of a computer aided detection system (CAD system). Twenty-four three-dimensional lung nodules were segmented and projected in five directions, mimicking 120 X-rayed nodules. The CAD system was tested by fivefold cross validation on a publicly available database. The results were evaluated by a free-response receiver operating characteristic analysis (FROC). It was found that the performance of the CAD system trained with simulated nodules comes close to the performance of state of the art CAD systems that are trained with real nodules. The CAD system trained with real nodules did improve by adding simulated nodules, but only when there were few real nodules used for training.