Standardized Method for the Detection of Patent Foramen Ovale Using Transcranial Colour-Coded Sonography, and Comparison of the Results with Transesophageal Echocardography [Pesquisa Protocolada de Foramen Oval Patente Com Doppler Transcraniano Codificado a Cor e Sua Comparação Com O Ecocardiograma Transesofágico]