Changes of nodule detection after radiologists read bone opacity suppressed chest radiography

A bone opacity suppressed technique using shape-index processing approach has been developed for frontal chest radiography. The image function preserves original lung image textures but equalizing the image contrast of the lungs as a part of post-processing. To determine the benefit of this computerized processing, particular on the investigation of the effect of the bone opacity removal, we conducted a reader study where radiologists read standard chest radiograph alone (unaided) followed by bone opacity suppressed image (aided). Posterioranterior (PA) standard chest radiographs in 368 subjects (122 had confirmed lung cancer) were used for this study. Fifteen Board Certified radiologists participated in the reader study. Each radiologist interpreted the standard image and then the bone suppressed image. Each reader recorded the location of the most suspicious nodule, if any, their level of suspicion and recommendation for clinical action. Detailed analyses were performed to evaluate the observers' performance by tabulating changes of nodule detection inclusive of false-negative turned to true-positive (FN->TP), true-positive turned to false-negative (TP->FN), false-positive turned to turn-negative (FP->TN), and turn-negative turned to false-positive (TN- >FP). Our results indicated that changing rates of FN->TP was 12.35%, TP->FN was 1.37%, FP->TN was 1.14%, and TN->FP was 4.82%, respectively. We also found that 81.85% of the FN->TP events occurred at nodules significantly covered by the rib (50% or more area overlapped with bone opacity). Two major situations caused TP->FN events: (1) other nodule like areas were also enhanced and (2) non-solid nodules were well preserved but less suspicious with the contract equalization.