Model-Based Perfusion Reconstruction with Time Separation Technique in Cone-Beam CT Dynamic Liver Perfusion Imaging

The success of embolisation, a minimally invasive treatment of liver cancer, could be evaluated in the operational room with cone-beam CT by acquiring a dynamic perfusion scan. The reconstruction algorithm must address the issues of low temporal sampling and higher noise levels inherent in cone-beam CT systems, compared to conventional CT. Therefore, a model-based perfusion reconstruction based on the time separation technique (TST) was applied. TST uses basis functions to model time attenuation curves. These functions are either analytical or based on prior knowledge, extracted using singular value decomposition from CT perfusion data. To explore how well the prior knowledge can model perfusion dynamics and what the potential limitations are, the dynamic CBCT perfusion scan was simulated under different noise levels. The TST method was compared to static reconstruction. It was demonstrated that a set consisting of only four basis functions results in perfusion maps that preserve relevant information, denoises the data, and outperforms static reconstruction under higher noise levels. TST with prior knowledge would not only outperform static reconstruction, but also the TST with analytical basis functions. Furthermore, it has been shown that only eight CBCT rotations, unlike previously assumed ten, are sufficient to obtain the perfusion maps comparable to the reference CT perfusion maps. This contributes to saving dose and reconstruction time. The real dynamic CBCT perfusion scan, reconstructed under the same conditions as the simulated scan, shows potential for maintaining the accuracy of the perfusion maps. By visual inspection, the embolised region was matching to that in corresponding CT perfusion maps. Further analysis of a larger cohort of patient data is needed to draw final conclusions regarding the expected advantages of the time separation technique.