Using the Fourth Dimension to Distinguish Between Structures for Anisotropic Diffusion Filtering in 4D CT Perfusion Scans

High resolution 4D (3D+time) cerebral CT perfusion (CTP) scans can be used to create 3D arteriograms (showing only arteries) and venograms (only veins). However, due to the low X-ray radiation dose used for acquiring the CTP scans, they are inherently noisy. In this paper, we propose a time intensity profile similarity (TIPS) anisotropic diffusion method that uses the 4th dimension to distinguish between structures, for reducing noise and enhancing arteries and veins in 4D CTP scans. The method was evaluated on 20 patient CTP scans. An observer study was performed by two radiologists, assessing the arteries and veins in arteriograms and venograms derived from the filtered CTP data, compared to those derived from the original data. Results showed that arteriograms and venograms derived from the filtered CTP data showed more and better visualized small arteries and veins in the majority of the 20 evaluated CTP scans. In conclusion, arteries and veins are separately enhanced and noise is reduced by using the time-intensity profile similarity (fourth dimension) to distinguish between structures for anisotropic diffusion filtering in 4D CT perfusion scans.