Relationship Between Tube Voltage and Physical Image Quality of Pulmonary Nodules on Chest Radiographs Obtained Using the Bone-Suppression Technique

Abstract

Image quality of chest radiographs is affected by tube voltage. This study aimed to clarify the relationship between tube voltage and physical image quality of pulmonary nodules on bone-suppressed chest radiographs. An anthropomorphic chest phantom and a spherical simulated nodule, with a 12-mm diameter and approximately +100 Hounsfield units were used. The lung field of the phantom was divided into three areas, based on the overlap with the ribs in the chest radiograph. Ten positions of the simulated nodule were defined in each area. One hundred and twenty chest radiographs were acquired using four tube voltages (70 kVp, 90 kVp, 110 kVp, and 130 kVp) for a total of 30 nodule positions and were processed to create bone-suppressed images. Differences in contrast and contrast-to-noise ratio (CNR) were analyzed for all pairs of the four tube voltages using a two-sided Wilcoxon signed-rank test. In the area not overlapping with ribs, a statistically significant difference was observed only in contrast between tube voltage of 70 kVp and 90 kVp (p = 0.01). In the area overlapping with one or two ribs, the contrast and CNR tended to be higher at a lower tube voltage. In particular, the p values between the contrast at 70 kVp and that at the other three tube voltage settings were less than 0.01. For a relatively dense nodule, the contrast and CNR in the bone-suppressed chest radiograph were significantly improved with lower tube voltage in the lung field overlapping with the ribs.