AI-based analysis of 3D position and orientation of red blood cells using a digital in-line holographic microscopy

The morphological and mechanical characteristics of red blood cells (RBCs) largely vary depending on the occurrence of hematologic disorders. Variations in the rheological properties of RBCs affect the dynamic motions of RBCs, especially their rotational behavior. However, conventional techniques for measuring the orientation of biconcave-shaped RBCs still have some technical limitations, including complicated optical setups, complex post data processing, and low throughput. In this study, we propose a novel image-based technique for measuring 3D position and orientation of normal RBCs using digital in-line holographic microscopy (DIHM) and artificial intelligence (AI). Formaldehyde-fixed RBCs are immobilized in coagulated polydimethylsiloxane (PDMS). Holographic images of RBCs positioned at various out-of-plane angles are acquired by precisely manipulating the PDMS-trapped RBC sample attached to a 4-axis optical stage. With the aid of deep learning algorithms for data augmentation and regression analysis, the out-of-plane angle of RBCs is directly predicted from the captured holographic images. The 3D position and in-plane angle of RBCs are acquired by employing numerical reconstruction and ellipse detection methods. Combining these digital image processing techniques, the 3D positional and orientational information of each RBC recorded in a single holographic image is measured within 23.5 and 3.07 s, respectively. The proposed AI-based DIHM technique that can extract the 3D position, orientation, and morphology of individual RBCs would be utilized to analyze the dynamic translational and rotational motions of abnormal RBCs with hematologic disorders in shear flows through further research.

A survey on design of reaction spheres and associated speed and orientation measurement technologies

With the rapid development of micro-spacecraft, miniaturization has become a key problem in attitude control. As an angular momentum exchange actuator, a single reaction sphere can generate multi-DOF output torques and satisfy the requirement of three-axis attitude control. This enables it to be a potential alternative for micro-spacecraft attitude control system. Categorized by the driving principles, the various design techniques of reaction spheres are firstly reviewed, including the spherical motor based and the multi-driving-wheels based. Their advantages and disadvantages are summarized. In order to realize the closed-loop control of the reaction sphere, the techniques of measuring the speed and orientation of the reaction spheres are subsequently reviewed. These include rotary encoders or gyroscope with gimbal guideway, photoelectric encoding ring, machine vision, Hall sensor, color sensor and piezoelectric sensor. By promoting the popularization of the concept of reaction spheres, it is expected to provide new ideas for the miniaturization design and attitude control of micro-spacecraft.