Recruitment Each patient referred to the vascular service with symptomatic SVI is assessed. Patients who potentially meet the inclusion criteria will be made aware of this research study and provided with the appropriate information, including the patient information sheet (see appendix 1). Patients will be given an opportunity to think about the invitation to participate and discuss with family/friends or other healthcare professionals if desired. Patients expressing an interest in participation will be offered an appointment for a screening visit with a study investigator.