A blood pool MRI contrast agent for free breathing MR angiography is highly desirable in particular for pediatric cardiovascular exams in order to improve both image quality and patient comfort. Apnea in infants and be propofol induced, or via intubation, which is invasive and limits acquisition to short protocols. We present here initial in-vivo studies in mice of a newly developed nanomicelles gadolinium contrast agent. Persistent vascular enhancement is observed with no toxicity. Micelles also open the way to functionalization for theranostic applications.