## 11 Conclusions and Future Prospects  
CXI is the most sensitive of the PCXI methods and has been used for fine observation in a wide range of fields, from biomedical to industrial. Several technical improvements to the CXI system are currently in progress.  
* Increasing SR energy (to 50 keV or higher) to increase X-ray transparency and thereby enable observation of thick and heavy samples such as biomedical samples, including calcification area, and semiconductor devices.
* Stabilization of phase detection by improvement of the image feedback system by installing a fast and sensitive X-ray imager to improve the density resolution below 0.1 mg/cm\({}^{3}\). Improvement of the spatial resolution below 10 \(\upmu\)m by thinning the crystal wafers to suppress the Borman fan effect (broaden X-ray beam in the wafer) [78]. These improvements are expected to lead to extremely fine observations and applications in various fields.
* Biomedical: quantitative diagnosis based on absolute density changes with aging, disease, and drug administration, functional imaging using novel PCXI contrast agents, and quantitative evaluation of the effectiveness of thermotherapy by three-dimensional X-ray thermography.
* Embryonic imaging: given that the resolution of optical microscopy in the serial section is a few micrometers, CXI functions as a 3D microscope when the resolution of CXI reaches 10 \(\upmu\)m. The whole body of a human embryo can be imaged with CXI, and 3D dynamic analysis of morphological changes during the embryonic stage is possible.
* Food: observation of the cooking process and evaluation of the relationship between heat and cooking conditions [79]. Quantitative analysis of the relationship between  
Figure 24: Schematic of sample cell (**left**) and three-dimensional temperature distribution of water heated using ceramic heater (**right**) [76].  
the density and elastic properties and food texture [80]. Evaluation of the freezing process and storage conditions [81].
* Earth environment: observation of the decomposition process of clathrate hydrate, evaluation of the relationship between crystallinity and density combined with XRD, and three-dimensional observation of phase transitions due to temperature change.
* Industrial: _Operand_ (in situ) observation of ion distribution in an electrolyte of various types of batteries for the optimization of their operation and charging/discharging conditions. Visualization of the internal temperature of devices such as LEDs and power semiconductor devices for optimal operation.
* Thermal engineering: visualization of dynamic thermal propagation (phonon propagation) in various materials such as thermoelectric conversion devices and laser ablation using a novel ps time-resolved pumps and probes method combining heating by pulsed laser irradiation and X-ray thermography using an X-ray free-electron laser [82].  
This research received no external funding.  
The animal experiments were approved by the Medical Committee for the Use of Animals in Research of the University of Tsukuba and the Animal Care and Use Committee of Kitasato University. They conformed to the guidelines of the American Physiological Society for animal experiments. The imaging and analyses using human embryos were approved by the Ethics Committee of Kyoto University.  
Not applicable.  
The authors declare no conflict of interest.  
We thank [PERSON] of Kitasato University for his useful advice. We are grateful to [PERSON] for her technical assistance at the beam line. Some observations were carried out under Proposal Nos. 2009S2-006, 2020G032, 2021G070, 2021G086, 2021G574, 2022G604, and 2022G611, approved by the High Energy Accelerator Research Organization.  
The authors declare no conflict of interest.