Dose optimization for digital chest radiography in phantom

INTRODUCTION: Chest radiography is a common radiological examination that is ordered for various objectives, including lung assessment of patients with COVID-19. Some patients may need to repeat many radiographs. Thus, the appropriate image quality for diagnosis with the optimal radiation exposure is necessary that the radiological technologist should consider. The purpose of this research is to study the exposure that provides the optimal radiation dose and image quality for supine position chest radiography. METHODS: The quality control of x-ray machine and digital image receptor was performed. The entrance surface air kerma (ESAK) was calculated to determine the setting parameters. Exposure parameters were obtained when the ESAK was lower than the Diagnostic reference level (DRL) of chest radiography. The consideration between the radiation dose and image quality was took place. Qualitative noise and image quality were scored by 3 observers. The quantitative analysis was evaluated in term of signal-to-noise ratio (SNR) by 3 regions at 4th ribs (1st ROI), 8th thoracic spine (2nd ROI) and left diaphragm (3rd ROI) and contrast-to-noise ratio was evaluated in 3 areas at rib area (1st area), thoracic spine (2nd area) and diaphragm area (3rd area). The optimal parameter is based on the image quality score and radiation dose. RESULTS: The optimal exposure parameter for phantom was 100 kVp and 0.4 mAs at 100 cm SID with 0.0528 mGy of ESAK. While, the observers scored on qualitative noise was 2 and image criteria were 4, 5.5 and 6. The average SNR in 1st, 2nd and 3rd ROIs were 45.03, 36.54 and 18.47, respectively. The average CNR in 1st, 2nd and 3rd areas were -1.22, -12.49 and 10.54, respectively. CONCLUSION: The optimal exposure parameter for chest radiography is 100 kVp and 0.4 mAs which maintains an acceptable image quality for diagnosis and optimal radiation dose that is lower than DRL in Thailand.