This study is a prospective multi-center observational study. Eligible patients will be enrolled in RelayBranch (NCT03214601). Participating centers must have capabilities of performing intra-operative TCD monitoring and post-operative TCD monitoring. If sites have performed TCD microembolic monitoring during previous RelayBranch procedures, we will also incorporate these data in our analysis. The primary objective is to assess the number and timing of cerebral microemboli during Relay®Branch thoracic stent-graft deployment, to identify the highest risk portions of the procedure. Secondary objectives include: correlate procedural microembolic burden with neuroimaging and clinical outcome; quantify post-operative microemboli, correlating with neuroimaging and clinical outcome; and quantify the changes in cerebral blood flow and cerebral autoregulation that happens during critical procedural epochs, correlating with neuroimaging and clinical outcome.
