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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.
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