Yan C, et al. - High-resolution optical coherence tomography (OCT) is suggested to be an excellent imaging technology for determining the microstructure of vessels. OCT has been used in this study to identify in situ thrombus within patent foramen ovale (PFO) of patients with and without stroke. In the adult population, 27.3% individuals have PFO and a number of pathological conditions, most importantly ischemic stroke, are associated with its presence. The main hypothesized mechanism is paradoxical embolism (from venous to systemic circulation), however, PFO itself has been suspected to be a site of thrombus formation. No definitive clinical evidence has been identified to support this mechanism.