Cardiac fiber tracking on super high-resolution CT images: a comparative study

Purpose: High-resolution cardiac imaging and fiber analysis methods are required to understand cardiac anatomy. Although refraction-contrast x-ray CT (RCT) has high soft tissue contrast, it cannot be commonly used because it requires a synchrotron system. Microfocus x-ray CT ( $\mu \mathrm{CT}$ ) is another commercially available imaging modality. Approach: We evaluate the usefulness of $\mu \mathrm{CT}$ for analyzing fibers by quantitatively and objectively comparing the results with RCT. To do so, we scanned a rabbit heart by both modalities with our original protocol of prepared materials and compared their image-based analysis results, including fiber orientation estimation and fiber tracking. Results: Fiber orientations estimated by two modalities were closely resembled under the correlation coefficient of 0.63. Tracked fibers from both modalities matched well the anatomical knowledge that fiber orientations are different inside and outside of the left ventricle. However, the $\mu \mathrm{CT}$ volume caused incorrect tracking around the boundaries caused by stitching scanning. Conclusions: Our experimental results demonstrated that $\mu \mathrm{CT}$ scanning can be used for cardiac fiber analysis, although further investigation is required in the differences of fiber analysis results on RCT and $\mu \mathrm{CT}$ .