Performance enhancement in wavefront shaping of multiply scattered light: a review

Significance

In nonballistic regime, optical scattering impedes high-resolution imaging through/inside complex media, such as milky liquid, fog, multimode fiber, and biological tissues, where confocal and multiphoton modalities fail. The significant tissue inhomogeneity-induced distortions need to be overcome and a technique referred as optical wavefront shaping (WFS), first proposed in 2007, has been becoming a promising solution, allowing for flexible and powerful light control. Understanding the principle and development of WFS may inspire exciting innovations for effective optical manipulation, imaging, stimulation, and therapy at depths in tissue or tissue-like complex media.

Aim

We aim to provide insights about what limits the WFS towards biomedical applications, and how recent efforts advance the performance of WFS among different trade-offs.

Approach

By differentiating the two implementation directions in the field, i.e., precompensation WFS and optical phase conjugation (OPC), improvement strategies are summarized and discussed.

Results

For biomedical applications, improving the speed of WFS is most essential in both directions, and a system-compatible wavefront modulator driven by fast apparatus is desired. In addition to that, algorithm efficiency and adaptability to perturbations/noise is of concern in precompensation WFS, while for OPC significant improvements rely heavily on integrating physical mechanisms and delicate system design for faster response and higher energy gain.

Conclusions

Substantial improvements in WFS implementations, from the aspects of physics, engineering, and computing, have inspired many novel and exciting optical applications that used to be optically inaccessible. It is envisioned that continuous efforts in the field can further advance WFS towards biomedical applications and guide our vision into deep biological tissues.

Can impoverished family nurture rich sons any more? The effect of household income on intergenerational transmission of education: Evidence from China

Family investment in education is an important variable influencing the educational attainment of children. Family investment in education is influenced by family income, and the increase in family income gap will aggravate the inequity of education and enhance the degree of intergenerational transmission of education. But the above theories need to be further tested in reality. This paper uses the 2018 China Family Panel Studies (CFPS) to verify the role of Chinese family income on intergenerational transmission of education through the education transition matrix and the mediating effect model, and examines the effect of college expansion policy on the mediating effect of family income on intergenerational transmission of education. The results show that: (1) The education level of parents has obvious transmissibility to the education level of children. The solidification rate of intergenerational transmission of education between parents and children is 25.72%, the upward mobility rate is 60.58% and the downward mobility rate is 13.70%. (2) The mediating effect model shows that the total effect of the parents' education level on children's education level is 0.279 and the direct effect is 0.272, and the family income plays a mediating effect in the intergenerational transmission of education, and the mediating degree reaches about 2.6%. (3) The expansion of higher education provides more opportunities for children of society, especially lower-middle-income families, to receive higher education, which weakens the mediating effect of family income in the intergenerational transmission of education. The findings of this paper provide support for policymakers to increase public investment in education.

Spectral CT using multiple balanced K-edge filters

Our goal is to validate a spectral computed tomography (CT) system design that uses a conventional X-ray source with multiple balanced K-edge filters. By performing a simultaneously synthetic reconstruction in multiple energy bins, we obtained a good agreement between measurements and model expectations for a reasonably complex phantom. We performed simulation and data acquisition on a phantom containing multiple rods of different materials using a NeuroLogica CT scanner. Five balanced K-edge filters including Molybdenum, Cerium, Dysprosium, Erbium, and Tungsten were used separately proximal to the X-ray tube. For each sinogram bin, measured filtered vector can be defined as a product of a transmission matrix, which is determined by the filters and is independent of the imaging object, and energy-binned intensity vector. The energy-binned sinograms were then obtained by inverting the transmission matrix followed by a multiplication of the filter measurement vector. For each energy bin defined by two consecutive K-edges, a synthesized energy-binned attenuation image was obtained using filtered back-projection reconstruction. The reconstructed attenuation coefficients for each rod obtained from the experiment was in good agreement with the corresponding simulated results. Furthermore, the reconstructed attenuation coefficients for a given energy bin, agreed with National Institute of Standards and Technology reference values when beam hardening within the energy bin is small. The proposed cost-effective system design using multiple balanced K-edge filters can be used to perform spectral CT imaging at clinically relevant flux rates using conventional detectors and integrating electronics.