Using Microbubble as Contrast Agent for High-Energy X-Ray In-line Phase Contrast Imaging: Demonstration and Comparison Study

The ability of microbubbles to benefit the imaging quality of high-energy in-line phase contrast as compared with conventional low-energy contact mode radiography was investigated. The study was conducted by comparing in-line phase contrast imaging with conventional contact-mode projection imaging under the same dose delivered to a phantom. A custom-designed phantom was employed to simulate a segment of human blood vessel injected with microbubble suspensions. The microbubbles were suspended in deionized water to obtain different volume concentrations. The area contrast-to-noise ratio (CNR) values corresponding to both imaging methods were measured for different microbubble volume concentrations. The phase contrast images were processed by phase-attenuation duality phase retrieval to preserve the imaging quality. Comparison of the resultant CNR values indicates that the microbubble suspension images deliver a higher CNR than the water-only image, with monotonically increasing trends between the CNR values and microbubble concentrations. Compared to low-energy conventional images of the microbubble suspensions, high-energy in-line phase contrast CNRs are lower at high concentrations and are comparable, even better than, at low concentrations. This result suggests that 1) the performance of copolymer-shell microbubble employed in this study as x-ray contrast agent is constrained by the detective quantum efficiency of the system and the attenuation properties of the shell materials, 2) the phase-attenuation duality phase retrieval method has the potential to preserve image quality for areas with low concentration of microbubbles, and 3) the selection of microbubble products as a phase contrast agent may follow criteria of minimizing the impact of absorption attenuation properties of the shells and maximizing the difference factor of electron densities.