Photon-counting detectors (PCD) not only have the advantage of providing spectral information but also offer high
quantum efficiencies, producing high image quality in combination with a minimal amount of radiation dose. Due to the
clinical unavailability of photon-counting CT, the need to evaluate different CT simulation tools for researching different
applications for photon-counting systems is essential. In this work, we investigate two different methods to simulate
PCD data: Monte-Carlo based simulation (MCS) and analytical based simulation (AS). The MCS is a general-purpose
photon transport simulation based on EGSnrc C++ class library. The AS uses analytical forward-projection in
combination with additional acquisition parameters. MCS takes into account all physical effects, but is computationally
expensive (several days per CT acquisition). AS is fast (several minutes), but lacks the accurateness of MCS with regard
to physical interactions. To evaluate both techniques an entrance spectra of 100kvp, a modified CTP515 module of the
CatPhan 600 phantom, and a detector system with six thresholds was simulated. For evaluation the simulated projection
data are decomposed via a maximum likelihood technique, and reconstructed via standard filtered-back projection (FBP).
Image quality from both methods is subjectively and objectively assessed. Visually, the difference in the image quality
was not significant. When further evaluated, the relative difference was below 4%. As a conclusion, both techniques
offer different advantages, while at different stages of development the accelerated calculations via AS can make a
significant difference. For the future one could foresee a combined method to join accuracy and speed.