A Novel Method for Predicting Pixel Value Distribution Non-uniformity Due to Heel Effect of X-ray Tube in Industrial Digital Radiography Using Artificial Neural Network

Abstract

The heel effect in X-ray radiation imaging systems causes a non-uniform radiation distribution on the imaging plane. In this research, a novel method was developed for predicting the pixel value’s non-uniformity due to the heel effect of X-ray tube on the imaging plane using Monte Carlo N particle (MCNP) simulation code and artificial neural network (ANN). At first, an industrial X-ray tube and a computed radiography (CR) image plate were simulated using MCNP. Then, the simulation procedure was benchmarked with an experiment. In the next step, nine images were obtained from the simulation for nine different tube voltages in the range of 100–300 kV. Furthermore, some pixels with tangential and polar angles in the range of 0°–20° and of 0°–180° with respect to the centered pixel were chosen from these nine simulated images in order to train the ANN, respectively. The tube voltage, tangential and polar angles of each pixel were used as the three inputs of the ANN and gray value in each pixel was used as the output. After training, the proposed ANN model could predict the gray value of each pixel on the imaging plane with mean relative error of less than 0.23%. In the last step, the predicted gray value difference between the centered pixel and other pixels was calculated. The great advantage of proposed methodology is providing the possibility of predicting the pixel value’s non-uniformity due to the heel effect of the X-ray tube on the imaging plane for a wide range of the tube voltages and source to film distances independent of the tube current and exposure time. Although the proposed methodology in this paper was developed for a specific X-ray tube and a CR imaging plate, it can be used for every digital radiography system.