The Evaluation of the Correlation between Radiographic Exposure Technique and Entrance Surface Air Kerma using Exposure Index from Computed Radiography

Abstract

Analog imaging system like Film-screen Radiography had been gradually replaced by Digital imaging system. Computed Radiography (CR) is the most common filmless system in Thailand. However, an adjustable digital image may induce unnecessary radiation exposure to patient. The KAP-meter, real time transmitted dosimeter, is quite expensive when consider as the radiographic examination cost. An Exposure Index (EI), a quantity derived from pixel value, is actually the indicator for image quality assessment used for patient dose monitoring. Objective:The aim of this study is to evaluate the correlation between Radiographic Exposure Technique and Entrance Surface Air KERMA (ESAK) using EI from CR. Methods: EI, ESAK, kVp, mAs of common radiographic procedures such as skull, chest, abdomen and pelvis were performed in anthropomorphic phantom and their correlations were analyzed by R(statistical data analysis software). Result: All procedures had strong correlation between EI and ESAK (p-value less than 0.01). The Pearson’s correlation (R) were 0.873, 0.901, 0.857, and 0.859 for skull, chest, abdomen, and pelvis respectively. Discussion and Conclusion:There was poor correlation between EI and kVp in this study. Hence kVp can affected x-ray beam quality this may alter the detective quantum efficiency (DQE) and conversion efficiency (CE) of CR. Further study ofextremities radiography should be performed. The comparison between our imaging system and that of the other system may encourage dose optimization.