Dual energy microCT for small animal bone-iodine decomposition

Dual Energy Computed Tomography (DECT) allows performing simple material separation or differentiation based on the energy dependence of the attenuation coefficient by acquiring an image at high and low energy. Up to date, many applications of DECT exist in clinical practice, but the translation of this method to preclinical systems has not been investigated thoroughly. The aim of this study is to validate the feasibility of bone - iodine separation using DECT on a standard FLEX Triumph-II system. Compared to clinical CT, microCT images are inherently prone to a higher amount of noise. A possible application may be found in vascular studies where scanning an animal at two different energies allows to separate the different iodine filled vascular structures from the surrounding non-vascular structures like bone. Using a density calibration phantom and different iodine concentrations, the optimal energy combination for preclinical DECT was determined. It was found that a 50-90 kVp energy pair was suited best to perform bone - iodine decomposition, without requiring additional filtration for the high- and low-energy scan. Next, a three material decomposition algorithm for bone, iodine and soft tissue was validated using the density calibration phantom. As this test yielded good results, a mouse study was performed to validate if similar results could be obtained in-vivo and ex-vivo. Based on the obtained results, we found that material separation using the standard FLEX Triumph-II system was possible both on phantoms and in-vivo. However, the in-vivo results still showed some iodine contributions in the bone image, possibly due to the simplicity of the decomposition algorithm. In the future, more complex, raw data based algorithms may be required together with the use of additional filtration and more advanced iterative reconstruction algorithms to achieve better spectral separation.