Recently, the research group of Profs. Qian Chen and Chao Zuo from the School of Electronic and Optical Engineering, Nanjing University of Science and Technology (NJUST) proposed a novel label-free, high-resolution 3D diffraction tomographic imaging technique. The related result, entitled “Transport-of-intensity Fourier ptychographic diffraction tomography: defying the matched illumination condition” was published in Optica. Optica, as the flagship journal of the Optical Society of America, is a top journal in the field of optics, with an impact factor of 10.64. Ph.D. candidate Shun Zhou and Dr. Jiaji Li of NJUST are the co-first authors of this paper, and Profs. Chao Zuo and Qian Chen are the co-corresponding authors. Article link: https://doi.org/10.1364/OPTICA.476474.
Optical diffraction tomography (ODT) is a very promising computational optical microscopic imaging technique that enables label-free, non-invasive 3D imaging of transparent biological samples. Different from the traditional imaging mode, i.e., “what you see is what you get”, ODT provides a simple and efficient solution for observing cellular life activities from higher dimensions and higher resolutions, which helps to explore the chemical essence and laws of life processes such as cell growth and differentiation, metabolism and reproduction, movement and communication, aging and apoptosis, genetics and evolution. This provides a more reliable scientific basis for exploring the causes, development, and treatment of major diseases.
However, traditional ODT techniques are based on interferometric or holographic measurements. The use of laser sources makes these ODT techniques suffer from inevitable speckle noise and parasitic interference, preventing high-quality 3D refractive index (RI) imaging. Moreover, most of them require specialized interferometric setups with complicated beam scanning, which are environmentally demanding and hardly compatible with existing optical microscopes, prohibiting their widespread application in the biological and medical communities. In recent years, non-interferometric ODT techniques have received increasing attention for their system simplicity, speckle-free imaging quality, and compatibility with existing microscopes. These techniques can directly recover the spatial RI distribution of the sample to be measured from the intensity information. However, ODT methods for implementing non-interferometric measurements in high numerical aperture (NA) microscopy systems are often plagued by low-frequency missing problems, resulting in obtaining high-quality RI tomograms hardly — a consequence of violating the matched illumination condition (illumination NA is equal to the objective NA).
Fig. 1. Hardware implementation and working flow of TI-FPDT
To address this technical challenge, the research group of Profs. Qian Chen and Chao Zuo proposed a high-resolution 3D microscopic imaging technique based on non-interferometric measurements, termed Transport-of-intensity Fourier ptychographic diffraction tomography (TI-FPDT). This technique combines the ptychographic angular diversity with additional transport-of-intensity measurements. By utilizing the defocused phase contrast in the defocused intensity images, FPDT overcomes the reconstruction quality deterioration and RI underestimation problems caused by non-matched illumination condition in conventional non-interferometric measurement methods. Therefore, TI-FPDT effectively circumvents the stringent requirement on the illumination NA imposed by the matched illumination condition and can achieve accurate 3D RI tomographic imaging of samples under arbitrary illumination conditions, thus making non-interferometric ODT under high-NA objectives possible. Due to its simplicity and effectiveness, TI-FPDT is anticipated to open new possibilities for label-free 3D microscopy in various biomedical applications.
This work was supported by the National Natural Science Foundation of China (61905115, 62105151, 62175109, U21B2033), and the National Major Scientific Instrument Development Project (62227818).
来源 | 南京理工大学
排版 | 孙菲
复审 | 左超
终审 | 徐峰