A technique for appropriate inferior collimation in chest radiography of asymptomatic negroid adults

Abstract

Background: Unnecessary exposure of the abdomen during chest radiography can lead to a substantial increase in radiation dose. Objective: To develop a new technique for reducing unnecessary abdominal irradiation during chest X-ray. Methodology: The work was designed to radiographically test the hypothesis that the umbilicus which is an external landmark that can both be seen and felt is the most appropriate anatomical landmark to consider as inferior collimation border in chest examinations. Computed tomography was used to confirm L3 and L4 as the corresponding dorsal bony landmark of the lower costal margin and umbilicus, respectively. Participants were radiographically examined with a collimation at an axial plane, 5.5 cm superior to the umbilicus. The maximum distance between the most inferior costophrenic angle and the collimation border on the radiograph was also determined. Data were manually tabulated. Results: The radiographs of 222 male and 216 female (n = 438) individuals were analyzed. 5.5 cm collimation coincided with L2 to T11 levels with 61% of individuals having costophrenic angles at T12 while only 3.7% had it high up at T10. No incidence of costophrenic angle cutoff was observed. Conclusion: Inferior collimation for chest X-ray in adults is adequate at an axial plane 5.5 cm superior to the umbilicus along the xipho-umbilical line on a patient at full inspiration. This point is a constant landmark when compared to X-ray beam centering point for chest radiography in the same patient which will be variable.