A Study of Quasi-Monochromatic X-Ray Sources for Breast Cancer Early Detection

Objectives: Early detection and treatment provide the opportunity to decrease the mortality rate from breast cancer. Quasi-monochromatic technique can enhance low contrast lesion detection by eliminating beam-hardening artifacts. We hypothesized that this technique would be feasible and can be used to assist in breast cancer early detection. Methods: The performance of stationary Digital Breast Tomosynthesis with quasi-monochromatic X-ray sources was evaluated using both simulated and physical phantoms. Normalized spectra in the fraction of total photons vs. photon energy were generated. Results: As expected, the peaked energies from sources, from smallest to largest, are Mo/Mo, W/Ag-1000, and W/Ce-10, W/Ce-100. For contrast vs. noise standard deviation on the simulated CIRS phantom, W/Ce-100 and W/Ce-10 have similar performance on both low and high contrast objects. For low contrast object, W/Ce-100 is barely noticeably better than W/Ce-10, and they are better than both W/Ag-1000 and Mo/Mo. For high contrast objects W/Ce-10 is slightly better than W/Ce-100. The spectra of the implemented W/Ce-10 X-ray source were measured, which matched the simulation well. The contrast noise ratios of reconstructed objects in American College of Radiology mammographic phantom with and without using W/Ce-10 combination are 7.1 and 5.4, respectively. Conclusions: The combination of stationary digital breast tomosynthesis and quasi-monochromatic technique can compensate the loss of X-ray flux due to heavy K-edge filtering. This technique can enable the stationary DBT scanners to operate at acceptable scanning times with better low contrast lesion detectability. Advances in Knowledge: The stationary digital breast tomosynthesis can provide high quality images within short scanning time by using X-ray source array, which makes quasi-monochromatic technique feasible.

High-quality quasi-monochromatic near-field radiative heat transfer designed by adaptive hybrid Bayesian optimization

The increasing demand for versatile and high-quality near-field radiative heat transfer(NFRHT) has created a critical need for a design approach that can handle numerous candidate structures. In this work, we employ and develop an adaptive hybrid Bayesian optimization(AHBO) algorithm to design the high-quality quasi-monochromatic NFRHT. The candidate materials include hexagonal boron nitride, silicon carbide, and doped silicon. The high-quality quasi-monochromatic NFRHT is optimized over 1.0 × 10^(8) candidate structures to maximize the evaluation factor. It is worth noting that only 2.6% of the candidate structures needed to be calculated to identify the optimal structure. The optimal structure of quasi-monochromatic NFRHT is an aperiodic multilayer metamaterial that differs from conventional periodic multilayer structures. Moreover, we investigate the robustness and mechanisms of the optimal quasi-monochromatic NFRHT with respect to the vacuum gap distance and the temperature difference between the emitter and receiver. In addition, the high-quality multi-peak NFRHT is designed using the AHBO algorithm by improving the definition of the evaluation factor. The results demonstrate that the AHBO algorithm is efficient in designing high-quality quasi-monochromatic and multi-peak NFRHT, and it can be further expanded to other structural designs in the field of energy conversion.

On Two-Dimensional Above-Barrier Penetration and Sub-Barrier Tunneling for Non-Relativistic Particles and Photons

We study the two-dimensional above-barrier penetration and the sub-barrier tunneling of non-relativistic particles and photons, described in the quasi-monochromatic approximation by simple plane waves. Our scheme represents the motion from the left free-motion zero-potential region to the right zero-potential region through the intermediate region with a one-dimensional rectangular potential barrier along the axis, normal to the both parallel interfaces between all three regions, and with the zero potential along the axis, parallel to the those interfaces. We have firstly obtained the analytical expressions for the infinite series of multiple internal and external reflections and also of multiple transmitted waves of particles and photons, with equal shifts between them along the interfaces for the above-barrier penetration and with various shifts between them in the case of the sub-barrier tunneling. Finally the Hartman and Fletcher effect for any transmitted wave is established.