Activation imaging: New concept of visualizing drug distribution with wide-band X-ray and gamma-ray imager

The visualization of drug distribution in the body plays an essential role in cancer therapy. Although various imaging methods have been proposed, a versatile method for visualizing multiple types of drugs is yet to be established. Therefore, we propose “activation imaging” as a new method for visualizing various drugs. Activation imaging activates drugs with protons or neutrons, enabling the visualization of drugs using gamma rays and/or X-rays emitted from the activated drugs. This method does not require labeling drugs with specific tracers because the constituent elements of the drugs become radiotracers through proton/neutron irradiation. Therefore, activation imaging can be used to visualize various types of existing drugs, including anticancer drugs, drug carriers, and contrast agents. In this study, we activated drugs using low-energy neutrons and performed gamma-ray spectroscopy and imaging. We used several types of drugs, such as cisplatin, a platinum-based anticancer drug; gold and platinum nanoparticles, which are promising drug carriers; and gadoteridol, a gadolinium-based contrast agent. Imaging was performed using a hybrid Compton camera, which can visualize X-rays and gamma rays ranging from a few tens of keV to nearly 1 MeV. With this wide-band X-ray and gamma-ray imager, various X-rays and gamma rays emitted from drugs can be visualized. Moreover, high-performance liquid chromatography (HPLC) was performed for cisplatin and gadoteridol to investigate whether the molecules of the drugs were degraded by neutron irradiation. Consequently, gamma rays from the activated drugs were observed in the spectra, and all drugs were successfully visualized. Furthermore, the HPLC results showed that most gadoteridol and cisplatin molecules retained their structure through activation.