Ex vivo imaging of the liver of rat injected with gadolinium contrast agents using MPPC-based photon counting CT

X-ray computed tomography (CT) is a technology that non destructively examines the interior of objects in three dimensions using X-rays. In conventional CT, the X-ray signal is converted into a current value and read out as the integrated form, resulting in the loss of energy information of X-rays. Therefore, it is difficult to distinguish target materials. Recently, a photon-counting CT (PC-CT) system has been developed as a future CT technology capable of detecting individual X-ray photons. In PC-CT, it is possible to distinguish target materials by examining the energy dependence of the attenuation coefficient value. Therefore, we developed a PC-CT system that combines high-speed scintillators and multi pixel photon counters (MPPCs) as photo-semiconductor devices. PC-CT can visualize the spatial distribution of some contrast agents accumulating selectively into human organs or specific receptors, which enables molecular imaging. The gadolinium-based contrast agent used for magnetic resonance imaging (MRI) has the property of being selectively taken up by the hepatocytes in the liver, which is useful for evaluating liver function and detecting lesions in the liver. If it is possible to create a similar or superior image using the gadolinium-based contrast agents in PC-CT as in MRI, it would be possible to diagnose patients not applicable to MRI. Therefore in this study, we extracted the liver from healthy rats injected with gadolinium contrast agent and performed ex vivo CT imaging of the contrast agent accumulated in the liver using PC-CT. Furthermore, we successfully visualized the distribution of gadolinium-based contrast agents accumulated in the liver with concentrations ranging from 1-5 mg/mL.