The unnecessary dose behind cropped radiographs

Objectives: In this study it was evaluated how common image cropping, or electronic collimation, is in digital radiography, how large an area of the images is cropped and how high the radiation dose is that corresponds to the cropped area.Methods: A sample of images were taken from three medical imaging departments. The images were reviewed; and if cropped, the extent was recorded. Results: A total of 1.270 images were reviewed. 10.6 % of them were cropped; 19 %, 7 % and 6 % in sites A, B and C, respectively. 26 % of all chest images were cropped as well as 18 %, 13 %, 10 %, 10 %, 3 % and 2 % of lumbar spine, shoulder, hip, knee, hand and foot images, respectively. The proportion of cropped images was significantly different between sites and between examinations (p < 0.05). Considering only the cropped images, the average cropped fraction of each image was from 16.0 % to 36.3 % and the corresponding unnecessary dose were estimated to be from 19.0 % to 56.9 % of the dose actually needed for the final image. Averaging the cropped area over all images in the same type of examination showed that up to 4.6 % of the dose in the examinations in the study was unnecessary. Conclusions: This study confirms that radiographs cropped, is a latent source of additional radiation dose to the patients. This needs be considered in the optimization of radiographic imaging procedures