Figure 1. Normal pericardium. (a) T₁ axial spin echo images show the pericardium as a narrow band of low signal intensity over the free wall of the right heart and the posterior wall of the left ventricle (arrows). (b) The space between the main pulmonary artery and the aorta (the aortopulmonary recess) (open arrow) is in continuity with the transverse sinus. Pericardial fluid may collect in this recess and potentially mimic the appearance of dissection.