Thesis (M.Sc.)--Chulalongkorn University, 2012

Dual energy subtraction technique is based on the different physical properties of soft-tissue and bony structure in the attenuation of x-ray photons at different x-ray energies. It produces two radiographs, one at higher kVp (bone image) and one at lower kVp (standard chest radiograph).The subtraction of a standard chest radiography and a bone image from the second CR plate produces a soft-tissue image. The purpose is to study the performance of the single shot dual-energy subtraction system in order to obtain the optimal protocol for chest radiography. Lung Man Chest phantom with simulated lesions diameter 3, 5, 8, 10, 12 mm were studied using a single shot DE subtraction system with different protocols on automatic exposure control. Optimal protocols result from the scores on qualitative evaluation by two radiologists and the entrance surface dose of phantom. The protocols were implemented to routine DE chest study in 65 patients. The image quality was scored by 2 radiologists of similar experience at three sets of images and evaluated ESD from clinical studies. Optimal protocol of this study is kVp at 120, -15% density, frequency rank 0, and frequency enhancement 0.3. ESD of chest projection in phantom study is 0.24 mGy. In patients study the average ESD was 0.22 (0.12- 0.58). The use of the DE subtraction method enhances the abnormal shadow detection capability especially in nodules at behind bone structure which can be seen in soft-tissue image rather than standard image only. However, the ultimate application of this technology can be used in clinical practice as an enlargement to existing imaging rather than as a replacement.