The human body is comprised of hundreds of bones, which are constantly regenerated through the interactions of two cell types: osteoblasts and osteoclasts. Given the difficulty of analyzing their intravital dynamics, we have developed a system for intravital imaging of the bone marrow cavity using two-photon microscopy, to visualize the dynamic behaviors of living bone cells without sectioning. Combined with the newly developed chemical fluorescent probes to detect localized acidification caused by osteoclasts, we identified two distinct functional states of mature osteoclasts, i.e., “bone-resorptive” and “non-resorptive”. Here, we focus on the dynamics and functions of bone cells within the bone marrow cavity and discuss how this novel approach has been applied to evaluate the mechanisms of action of drugs currently in clinical use. We further introduce our recent study that identified arthritis-associated osteoclastogenic macrophages in inflamed synovium and revealed their differentiation trajectory into the pathological osteoclasts, which together represent to a new paradigm in bone research.

This report highlights the usefulness and applicability of various gravimetric methods for studying earthquakes and volcanic activities. A high-resolution gravity anomaly map of Japan reveals areas with very steep horizontal gradients, where potential seismic faults are likely to be buried. Such traditional geoprospecting is coupled with novel cosmic-ray radiography to produce a fine-resolution (<100 m) three-dimensional density structure of a volcano. On the other hand, temporal gravity changes provide invaluable information about the process of earthquake faulting, volcanic eruptions, caldera formation, etc. Specifically, in this report we present our previous work on gravity research for solid earth science: (1) the first detection of coseismic gravity changes, (2) the virtual visualization of the rising and falling of magma in a conduit of Asama volcano, and (3) the large-scale lateral movement of magma during the Miyake-jima eruption in 2000.

Responding to the radiation-related concerns of parents/guardians with infants/small children is an important public health issue for regional recovery after radioactive contamination. This study summarizes the results of a systematic internal contamination screening of infants/small children, aged 0–6 years, using BABYSCAN and individual counselling sessions with physicians about radiation concerns from 2014 to 2018 in Minamisoma City. Of 3,114 participants, no one was found to have internal contamination with radioactive caesium with a detection limit of 50 Bq/body. The questionnaire survey showed a decreasing trend of concerns about food contamination and playing outside as possible causes of internal contamination over time. Because people’s concerns were diverse in counselling sessions, individual responses are required. This study showed that examinations using BABYSCAN provide an opportunity for direct dialogue between the parents/guardians of infants/small children and experts. This can be considered a model case for risk communication conducted by the local government after a radioactive contamination incident.