Purpose: To assess the performance of a Dual-Energy chest radiography system. Methods:A cohort of 129 patients was recruited from population referred for CT guided biopsy of a lung lesion. Digital radiography (DR) and Dual Energy (DE) images were acquired.Receiver operating characteristic (ROC) tests were performed to evaluate performance of DE images compared to DR. Five chest radiologists scored images. Performance was analyzed for all cases pooled and sub groups based on gender, nodule size, density, location, and chest diameter.

Dual-energy ͑DE͒ imaging of the chest improves the conspicuity of subtle lung nodules through the removal of overlying anatomical noise. Recent work has shown double-shot DE imaging ͑i.e., successive acquisition of low-and high-energy projections͒ to provide detective quantum efficiency, spectral separation ͑and therefore contrast͒, and radiation dose superior to single-shot DE imaging configurations ͑e.g., with a CR cassette͒. However, the temporal separation between highenergy ͑HE͒ and low-energy ͑LE͒ image acquisition can result in motion artifacts in the DE images, reducing image quality and diminishing diagnostic performance. This has motivated the development of a deformable registration technique that aligns the HE image onto the LE image before DE decomposition. The algorithm reported here operates in multiple passes at progressively smaller scales and increasing resolution. The first pass addresses large-scale motion by means of mutual information optimization, while successive passes ͑2-4͒ correct misregistration at finer scales by means of normalized cross correlation. Evaluation of registration performance in 129 patients imaged using an experimental DE imaging prototype demonstrated a statistically significant improvement in image alignment. Specific to the cardiac region, the registration algorithm was found to outperform a simple cardiac-gating system designed to trigger both HE and LE exposures during diastole. Modulation transfer function ͑MTF͒ analysis reveals additional advantages in DE image quality in terms of noise reduction and edge enhancement. This algorithm could offer an important tool in enhancing DE image quality and potentially improving diagnostic performance.

Rationale and Objectives-To assess the performance of a newly developed dual-energy (DE) chest radiography system in comparison to digital radiography (DR) in the detection and characterization of lung nodules.Materials and Methods-An experimental prototype has been developed for high-performance DE chest imaging with total dose equivalent to a single posterior-anterior DR image. Low-and highkVp projections were used to decompose DE soft-tissue and bone images. A cohort of 55 patients (31 male, 24 female, mean age 65.6 years) was drawn from an ongoing trial involving patients referred for percutaneous CT guided biopsy of suspicious lung nodules. DE and DR images were acquired of each patient prior to biopsy. Image quality was assessed by means of human observer tests involving 5 radiologists independently rating the detection and characterization of lung nodules on a 9-point scale. Results were analyzed in terms of the fraction of cases at or above a given rating, and statistical significance was evaluated from a Wilcoxon signed rank test. Performance was analyzed for all cases pooled as well as by stratification of nodule size, density, lung region, and chest thickness.Results-The studies demonstrate a significant performance advantage for DE imaging compared to DR (p<0.001) in the detection and characterization of lung nodules. DE imaging improved the detection of both small and large nodules and exhibited the most significant improvement in regions of the upper lobes, where overlying anatomical noise (ribs and clavicles) are believed to reduce nodule conspicuity in DR.Conclusions-DE imaging outperformed DR overall, particularly in the detection of small, solid nodules. DE imaging also performed better in regions dominated by anatomical noise such as the lung apices. The potential for improved nodule detection and characterization at radiation doses equivalent to DR is encouraging and could augment broader utilization of DE imaging. F studies will