I’ve been using Siemens’ WIP (work-in-progress) 4D Flow MRI sequence for the past few months, and I’ve encountered an occasional issue. In 3 out of 20 cardiac phases, there is a complete reversal of flow in all vessels across the image, in every direction. Left-to-right flow appears as right-to-left, anterior-to-posterior shows as posterior-to-anterior, and so on. I haven’t been able to identify the cause of this anomaly. I’ve been scanning both the brain and chest, but this problem only occurs in some of the brain scans, despite using an adequate venc setting. Both Siemens and our techs suspect aliasing, but the issue seems different from typical aliasing artifacts. I’ve also attempted phase unwrapping with various commercial software, but it hasn’t resolved the problem.
Hoping for some insight as well as possible fixes. Tysm!