Effect of vertical positioning on organ dose, image noise and contrast in pediatric chest CT - Phantom study

Background: CT optimization has a special importance in children. Smaller body size accentuates the importance of patient positioning affecting both radiation dose and image quality. Objective: To determine the effect of vertical positioning on organ dose, image noise and contrast in pediatric chest CT examination. Materials and methods: Chest scans of a pediatric 5-year anthropomorphic phantom were performed in different vertical positions (-6 cm to +5.4 cm) with a 64-slice CT scanner. Organ doses were measured with metal-oxide-semiconductor field-effect transistor (MOSFET) dosimeters. Image noise and contrast were determined from the CT number histograms corresponding to different tissues. Results: Significant changes in organ doses resulting from vertical positioning were observed, especially in radiosensitive anterior organs. The breast dose increased up to 16% and the thyroid dose up to 24% in lower positions. The noise was increased up to 45% relative to the centre position in the highest and lowest vertical positions, with a particular increase observed on the anterior and posterior sides, respectively. Off-centering also affected measured image contrast. Conclusion: Vertical off-centering markedly affects organ doses and measured image-quality parameters in pediatric chest CT examination. Special attention should be given to correct patient centering when preparing patients for CT scans, especially when imaging children.