Hiroshi Kunitomo

PURPOSE: To evaluate image quality for chest radiography at different radiation qualities, using phantoms with scatter fractions similar to those of lungs. METHODS: Two base phantoms with 10 and 4 cm thicknesses, respectively, made of a soft tissue-equivalent material, were used to mimic the X-ray attenuation of the human lung. Two plates with soft tissue- and bone-equivalent materials, respectively, were placed on the base phantom as contrast objects. The image data were obtained with the same entrance surface dose in each radiation quality. Six radiation qualities generated using 120 and 90 kV, and additional copper filters with thicknesses 0, 0.1, and 0.2 mm were selected. The signal-difference-to-noise ratio (SdNR) and a contrast ratio of the soft tissue to the bone were measured for the six radiation qualities. RESULTS: The thicker the additional filter, the better the SdNR at both tube voltages. The SdNR values were not significantly different between 120 and 90 kV for the same filter thickness. The contrast ratio was higher at 120 than at 90 kV by approximately 8%. CONCLUSIONS: Because of the advantage of the contrast ratio and the highest SdNR, the radiation quality with 120 kV and 0.2-mm copper filtration was the best. It was indicated that the conventional tube voltage of 120 kV remains to be better than the lower tube voltage of 90 kV.

Mammography equipment attached to the digital breast tomosynthesis (DBT) system is widespread in Japan. However, there are no guidelines for quality control methods for DBT in Japan. Therefore, it is necessary to rapidly establish a performance evaluation procedure and a quality control procedure for DBT. In this study, we conducted basic experiments using DBTs of five companies (Canon Medical, Fujifilm Medical, GE Healthcare, Hologic, Siemens) already sold in Japan and examined feasible common items. We aimed to establish a quality control method for DBT in Japan. The measurement was performed based on the European Reference Organisation for Quality Assured Breast Screening and Diagnostic Services (EUREF) breast tomosynthesis quality control protocol, version 1.03. In this study, we tried to measure 18 items in DBT. We examined whether the 18 items could be measured using each device; it is not an evaluation of device performance based on the measured values. There were some management items that were difficult to implement due to the specifications of DBT, such as devices that required pressure on DBT operation, problems due to the shape of bucky, and devices that did not have stationary mode. There were also problems with measurement data; for example, devices could not retrieve projection data and reconstruction data. This study clarified points to be considered for establishing common quality control items. In the future, we will carefully refer to the recently published IEC 61223-3-6, consider international harmonization, and establish DBT guidelines customized for the Japanese market.