Quantitative Analysis of the Additional Radiation Burden due to Electronic Collimation in Digital Radiography

Abstract

Abstract: In recent years, the conventional film-screen radiography technique is replaced with the novel invention of digital radiography. This digital technology provides prompt image readout with reduced radiation exposure. The image can be post processed to adjust the spatial resolution and contrast. However, the inappropriate use of the background masking tool during post processing degrades the outcomes of the digital technology. Although this tool is intended to eliminate the ambient light around an image to improve the quality of the displayed image, contrary it is used as a substitute for insufficient pre-exposure collimation of the irradiated field resulting in unnecessary overexposure. The present study aimed at evaluating additional radiation dose due to electronic cropping in digital radiography facility for the first time in Sri Lanka. A sample of 194 X-ray images under nine different projections was evaluated and the average areas of pre and post-exposure collimation were measured. The difference of the mean areas was calculated and presented as a percentage of the area of the whole radiation field. The percentage of overexposed area due to improper collimation was found to be over 50% in cervical spine, shoulder and sinus projections (in 44.4% of study sample). The lateral projection of cervical spine showed the highest overexposed percentage (55%). Therefore, it is within the scope of practice of a radiologic technologist to use appropriate preexposure collimation. The electronic masking should be only utilized to eliminate the interfering brightness in the image and the technologists should be clinically competent to adopt the above concept.