Trajectory planning: Real time CMR pericardiocentesis. Real-time CMR system user interface (Interactive Front End, Siemens Corporate Research, Princeton) is used for trajectory planning. The prescribed slice planes intersect along the projected needle path. The operator finger (white arrow) depresses the subxiphoid skin surface to mark the proposed needle entry site. Panel A (coronal) and B (sagittal) is an animal with a large (150 ml) effusion. Panel C (coronal) and D (sagittal) is an animal with no effusion. Posterior trajectory is chosen. The blue dotted line indicates an axial imaging plane prescription that is not shown.