RADIATION DOSE AND IMAGE QUALITY IN CHEST REGION USING SINGLE- AND DUAL-ENERGY CT: PHANTOM STUDY

Abstract

Chest CT examinations are routinely performed by using single energy protocol (SE). As CT had been evolved by using dual energy protocol (DE), the patients with underlying lung nodules or pulmonary nodules will be followed up by CT examination several times. The purpose of this study is to study the radiation dose and image quality between single-energy CT (SECT) and dual-energy CT (DECT) protocols in chest phantom at King Chulalongkorn Memorial Hospital. The Lungman Kyoto Kagaku phantom inserted by five simulated lesions of various diameters was scanned by dual-source CT system (Somatom Force, Siemens Healthineers). The acquisition protocols consist of single-energy and dual-energy modes with varied tube potential. Radiation dose is determined in terms of CTDI volume (CTDIvol), Dose Length Product (DLP) and effective dose. Image noise, CNR and lesion detectability are the image quality indicators in this study. The results of this study show that the mean value of radiation dose in SE at 120 kVp was highest among all acquisition protocols, which results in lower image noise than DE. CNR of DE at 100/Sn150 kVp was greater than 120 kVp, all SE protocols, DE at 80/Sn150 and 90/Sn150. Regarding lesion detectability, in the soft tissue window, the simulated lesions were detected by the observers in dual energy mode as similar to in single-energy mode at 120 kVp. Moreover, in the lung window, all observers can detect the simulated lesions better than in soft tissue window, which results in five lesions were detected in both single- and dual- energy protocols, the same as CT lung CAD software could detect five simulated lesions. Therefore, DECT offers an alternative protocol for lung nodule detection because DECT offer lower radiation dose than SECT (120 kVp), clinical protocol in chest CT examination, in addition to lesion detectability DECT is similar to 120 kVp. In contrast, the image noise of DECT is higher than 120 kVp that affect the interpretation of radiologist. Therefore, DE protocols can be selected under the justification of qualified CT radiologist with the optimal protocol in chest CT examination.