Purpose: Conventional x-ray imaging provides limited quantitative information due to scatter, beam hardening, and overlaying tissues. A single-shot quantitative x-ray imaging (SSQI) method proposed in this work quantifies material-specific densities in x-ray imaging by combining the use of a primary modulator (PM) and a dual-layer (DL) detector.
Methods: The PM features a checkerboard arrangement of alternating unattenuated and partially attenuated squares. Conceptually, the PM performs scatter correction for the DL images, while the DL images remove beam hardening from the PM. The DL detector further generates low- and high-energy images with superior registration, which are used to create material-specific images. In this work, a simulation study was performed for chest x-ray to test the feasibility of SSQI. We first simulated the x-ray images of a digital phantom (Lungman, Kyoto Kaguku) by incorporating a 120 kV spectrum, PM, and DL detector, and including scatter. The DL images contained four measurements that were obtained behind the hole (unattenuated) and fill (partially attenuated) regions of the PM of each layer. Using the low-frequency property of scatter and a pre-calibrated material decomposition (MD), four unknowns (i.e., two scatter images and two material-specific images) were jointly recovered by directly solving four equations given by the four measurements.
Results: SSQI accurately performed MD to separate soft tissue from bone. Its performance improved with a smaller PM pitch and reduced focal spot blur. A pitch of 457 μm and source-to-modulator distance of 36.3 cm can be an optimal combination for practical use, reducing the RMSE by 80% and 96% for PMMA and copper MD images, respectively, as compared to without scatter correction.
Conclusion: We demonstrated the feasibility of SSQI to perform MD that is robust against scatter. The simplicity of SSQI may enable its widespread adoption beyond x-ray imaging to real-time image guidance and cone-beam CT.